bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple visual pigments in a photoreceptor of the salamander retina.
Authors: Makino C L , Dodd R L
Published: May 2004

Although a given retina typically contains several visual pigments, each formed from a retinal chromophore bound to a specific opsin protein, single photoreceptor cells have been thought to express only one type of opsin. This design maximizes a cell's sensitivity to a particular wavelength band and facilitates wavelength discrimination in retinas that process color. We report electrophysiological evidence that the ultraviolet-sensitive cone of salamander violates this rule. This cell contains three different functional opsins. The three opsins could combine with the two different chromophores present in salamander retina to form six visual pigments. Whereas rods and other cones of salamander use both chromophores, they appear to express only one type of opsin per cell. In visual pigment absorption spectra, the bandwidth at half-maximal sensitivity increases as the pigment's wavelength maximum decreases. However, the bandwidth of the UV-absorbing pigment deviates from this trend; it is narrow like that of a red-absorbing pigment. In addition, the UV-absorbing pigment has a high apparent photosensitivity when compared with that of red- and blue-absorbing pigments and rhodopsin. These properties suggest that the mechanisms responsible for spectrally tuning visual pigments separate two absorption bands as the wavelength of maximal sensitivity shifts from UV to long wavelengths.
Protein kinase regulation of a cloned epithelial Na+ channel.
Authors: Awayda M S , Ismailov I I , Berdiev B K , Fuller C M , Benos D J
Published: May 2004

We examined the regulation of a cloned epithelial Na+ channel (alpha beta gamma-rENaC) by protein kinase A (PKA) and protein kinase C (PKC). Experiments were performed in Xenopus oocytes and in planar lipid bilayers. At a holding potential of -100 mV, amiloride-sensitive current averaged -1,279 +/- 111 nA (n = 7) in alpha beta gamma-rENaC-expressing oocytes. Currents in water-injected oocytes were essentially unresponsive to 10 microM amiloride. A 1-h stimulation of PKC with 100 nM of PMA inhibited whole-cell currents in Xenopus oocytes to 17.1 +/- 1.8, and 22.1 +/- 2.6% of control (n = 7), at holding potentials of -100 and +40 mV, respectively. Direct injection of purified PKC resulted in similar inhibition to that observed with PMA. Additionally, the inactive phorbol ester, phorbol-12-myristate-13-acetate, 4-O-methyl, was without effect on alpha beta gamma-rENaC currents. Pretreatment with the microtubule inhibitor colchicine (100 microM) did not modify the inhibitory effect of PMA; however, pretreatment with 20 microM cytochalasin B decreased the inhibitory action of PMA to < 20% of that previously observed. In vitro-synthesized alpha beta gamma-rENaC formed an amiloride-sensitive Na(+)-selective channel when incorporated into planar lipid bilayers. Addition of PKC, diacyl-glycerol, and Mg-ATP to the side opposite that which amiloride blocked, decreased the channel's open probability (Po) from 0.44 +/- 0.06 to 0.13 +/- 0.03 (n = 9). To study the effects of PKA on alpha beta gamma-rENaC expressed in Xenopus oocytes, cAMP levels were elevated with 10 microM forskolin and 1 mM isobutyl-methyl-xanthine. This cAMP-elevating cocktail did not cause any stimulation of alpha beta gamma-rENaC currents in either the inward or outward directions. This lack of activation was also observed in oocytes preinhibited with PMA and in oocytes pretreated with cytochalasin B and PMA. Neither alpha-rENaC nor alpha beta gamma-rENaC incorporated into planar lipid bilayers could be activated with PKA and Mg-ATP added to either side of the membrane, as Po remained at 0.63 +/- 0.06 (n = 7) and 0.45 +/- 0.05 (n = 9), respectively. We conclude that: alpha beta gamma-rENaC is inhibited by PKC, and that alpha beta gamma-rENaC is not activated by PKA.
Anomalous regulation of the Drosophila Na(+)-Ca2+ exchanger by Ca2+.
Authors: Hryshko L V , Matsuoka S , Nicoll D A , Weiss J N , Schwarz E M , Benzer S , Philipson K D
Published: May 2004

The Na(+)-Ca2+ exchanger from Drosophila was expressed in Xenopus and characterized electrophysiologically using the giant excised patch technique. This protein, termed Calx, shares 49% amino acid identity to the canine cardiac Na(+)-Ca2+ exchanger, NCX1. Calx exhibits properties similar to previously characterized Na(+)-Ca2+ exchangers including intracellular Na+ affinities, current-voltage relationships, and sensitivity to the peptide inhibitor, XIP. However, the Drosophila Na(+)-Ca2+ exchanger shows a completely opposite response to cytoplasmic Ca2+. Previously cloned Na(+)-Ca2+ exchangers (NCX1 and NCX2) are stimulated by cytoplasmic Ca2+ in the micromolar range (0.1-10 microM). This stimulation of exchange current is mediated by occupancy of a regulatory Ca2+ binding site separate from the Ca2+ transport site. In contrast, Calx is inhibited by cytoplasmic Ca2+ over this same concentration range. The inhibition of exchange current is evident for both forward and reverse modes of transport. The characteristics of the inhibition are consistent with the binding of Ca2+ at a regulatory site distinct from the transport site. These data provide a rational basis for subsequent structure-function studies targeting the intracellular Ca2+ regulatory mechanism.
The inositol 1,4,5-trisphosphate receptor of cerebellum. Mn2+ permeability and regulation by cytosolic Mn2+.
Authors: Striggow F , Ehrlich B E
Published: May 2004

The inositol 1,4,5-trisphosphate receptor (InsP3R), an intracellular calcium release channel, is found in virtually all cells and is abundant in the cerebellum. We used Mn2+ as a tool to study two aspects of the cerebellar InsP3R. First, to investigate the structure of the ion pore, Mn2+ permeation through the channel was determined. We found that Mn2+ can pass through the InsP3R; the selectivity sequence for divalent cations is Ba2+ > Sr2+ > Ca2+ > Mg2+ > Mn2+. Second, to begin characterization of the cytosolic regulatory sites responsible for the Ca(2+)-dependent modulation of InsP3R function, the ability of Mn2+ to replace Ca2+ was investigated. We show that Mn2+, as Ca2+, modulates InsP3R activity with a bell-shaped dependence where the affinity of the activation site of the InsP3R is similar for both ions, but higher concentrations of Mn2+ were necessary to inhibit the channel. These results suggest that the two regulatory sites are structurally distinct. Our findings are also important for the understanding of cellular responses when Mn2+ is used to quench the intracellular fluorescence of Ca2+ indicator dyes.
Transalveolar osmotic and diffusional water permeability in intact mouse lung measured by a novel surface fluorescence method.
Authors: Carter E P , Matthay M A , Farinas J , Verkman A S
Published: May 2004

A surface fluorescence method was developed to measure transalveolar transport of water, protons, and solutes in intact perfused lungs. Lungs from c57 mice were removed and perfused via the pulmonary artery (approximately 2 ml/min). The airspace was filled via the trachea with physiological saline containing a membrane-impermeant fluorescent indicator (FITC-dextran or aminonapthalene trisulfonic acid, ANTS). Because fluorescence is detected only near the lung surface due to light absorption by lung tissue, the surface fluorescence signal is directly proportional to indicator concentration. Confocal microscopy confirmed that the fluorescence signal arises from fluorophores in alveoli just beneath the pleural surface. Osmotic water permeability (Pf) was measured from the time course of intraalveolar FITC-dextran fluorescence in response to changes in perfusate osmolality. Transalveolar Pf was 0.017 +/- 0.001 cm/s at 23 degrees C, independent of the solute used to induce osmosis (sucrose, NaCl, urea), independent of osmotic gradient size and direction, weakly temperature dependent (Arrhenius activation energy 5.3 kcal/mol) and inhibited by HgCl2. Pf was not affected by cAMP activation but was decreased by 43% in lung exposed to hyperoxia for 5 d. Diffusional water permeability (Pd) and Pf were measured in the same lung from intraalveolar ANTS fluorescence, which increased by 1.8-fold upon addition of 50% D2O to the perfusate, Pd was 1.3 x 10(-5) cm/s at 23 degrees C. Transalveolar proton transport was measured from FITC-dextran fluorescence upon switching perfusate pH between 7.4 and 5.6; alveolar pH half-equilibrated in 1.9 and 1.0 min without and with HCO3-, respectively. These results indicate high transalveolar water permeability in mouse lung, implicating the involvement of molecular water channels, and establish a quantitative surface fluorescence method to measure water and solute permeabilities in intact lung.
Activation of different Cl currents in Xenopus oocytes by Ca liberated from stores and by capacitative Ca influx.
Authors: Hartzell H C
Published: May 2004

Xenopus oocytes are an excellent model system for studying Ca signaling. The purpose of this study was to characterize in detail the Ca-activated Cl currents evoked by injection of inositol 1,4,5-trisphosphate (IP3) into Xenopus oocytes voltage-clamped with two microelectrodes. Injection of IP3 into Xenopus oocytes activates two different Ca-activated Cl currents. ICl-1 is stimulated rapidly (within 5 s after IP3 injection), exhibits time-dependent activation upon depolarization, a linear instantaneous IV relationship with a reversal potential near ECl, and a curvilinear activation curve with an approximate half-maximal activation voltage of > 200 mV. ICl-2D is stimulated slowly after IP3 injection (half-maximal stimulation occurs approximately 3 min after injection). ICl-2D has a strongly outwardly rectifying instantaneous IV relationship with a reversal potential near ECl and is activated by hyperpolarization with a half-maximal activation voltage of -105 mV. ICl-2D cannot be activated by Ca released from stores but is activated by Ca influx. In contrast, ICl-1 can be stimulated by Ca released from intracellular Ca stores. It can also be stimulated by Ca influx through store-operated channels if the Ca driving force is increased by a hyperpolarization immediately before the depolarization that gates ICl-1 channels. The description of two currents activated by influx and Ca release from stores provides new insights into and questions about the regulation of Ca in Xenopus oocytes.
Cell swelling activates ATP-dependent voltage-gated chloride channels in M-1 mouse cortical collecting duct cells.
Authors: Meyer K , Korbmacher C
Published: May 2004

In the present study we used whole-cell patch clamp recordings to investigate swelling-activated Cl-currents (ICl-swell) in M-1 mouse cortical collecting duct (CCD) cells. Hypotonic cell swelling reversibly increased the whole-cell Cl- conductance by about 30-fold. The I-V relationship was outwardly-rectifying and ICl-swell displayed a characteristic voltage-dependence with relatively fast inactivation upon large depolarizing and slow activation upon hyperpolarizing voltage steps. Reversal potential measurements revealed a selectivity sequence SCN- > I- > Br- > Cl- > > gluconate. ICl-swell was inhibited by tamoxifen, NPPB (5-nitro-2(3-phenylpropylamino)-benzoate), DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid), flufenamic acid, niflumic acid, and glibenclamide, in descending order of potency. Extracellular cAMP had no significant effect. ICl-swell was Ca2+ independent, but current activation depended on the presence of a high-energy gamma-phosphate group from intracellular ATP or ATP gamma S. Moreover, it depended on the presence of intracellular Mg2+ and was inhibited by staurosporine, which indicates that a phosphorylation step is involved in channel activation. Increasing the cytosolic Ca2+ concentration by using ionomycin stimulated Cl- currents with a voltage dependence different from that of ICl-swell. Analysis of whole-cell current records during early onset of ICl-swell and during final recovery revealed discontinuous step-like changes of the whole-cell current level which were not observed under nonswelling conditions. A single-channel I-V curve constructed using the smallest resolvable current transitions detected at various holding potentials and revealed a slope conductance of 55, 15, and 8 pS at +120, 0, and -120 mV, respectively. The larger current steps observed in these recordings had about 2, 3, or 4 times the size of the putative single-channel current amplitude, suggesting a coordinated gating of several individual channels or channel subunits. In conclusion we have functionally characterized ICl-swell in M-1 CCD cells and have identified the underlying single channels in whole-cell current recordings.
N-type inactivation and the S4-S5 region of the Shaker K+ channel.
Authors: Holmgren M , Jurman M E , Yellen G
Published: May 2004

The intracellular segment of the Shaker K+ channel between transmembrane domains S4 and S5 has been proposed to form at least part of the receptor for the tethered N-type inactivation "ball." We used the approach of cysteine substitution mutagenesis and chemical modification to test the importance of this region in N-type inactivation. We studied N-type inactivation or the block by a soluble inactivation peptide ("ball peptide") before and after chemical modification by methanethiosulfonate reagents. Particularly at position 391, chemical modification altered specifically the kinetics of ball peptide binding without altering other biophysical properties of the channel. Results with reagents that attach different charged groups at 391 C suggested that there are both electrostatic and steric interactions between this site and the ball peptide. These findings identify this site to be in or near the receptor site for the inactivation ball. At many of the other positions studied, modification noticeably inhibited channel current. The accessible cysteines varied in the state-dependence of their modification, with five- to tenfold changes in reactions rate depending on the gating state of the channel.
Adrenocorticotropic hormone and cAMP inhibit noninactivating K+ current in adrenocortical cells by an A-kinase-independent mechanism requiring ATP hydrolysis.
Authors: Enyeart J J , Mlinar B , Enyeart J A
Published: May 2004

Bovine adrenal zona fasciculata (AZF) cells express a noninactivating K+ current (IAC) that is inhibited by adrenocorticotropic hormone (ACTH) at picomolar concentrations. Inhibition of IAC may be a critical step in depolarization-dependent Ca2+ entry leading to cortisol secretion. In whole-cell patch clamp recordings from AZF cells, we have characterized properties of IAC and the signalling pathway by which ACTH inhibits this current. IAC was identified as a voltage-gated, outwardly rectifying, K(+)-selective current whose inhibition by ACTH required activation of a pertussis toxin-insensitive GTP binding protein. IAC was selectively inhibited by the cAMP analogue 8-(4-chlorophenylthio)-adenosine 3':5'-cyclic monophosphate (8-pcpt-cAMP) with an IC50 of 160 microM. The adenylate cyclase activator forskolin (2.5 microM) also reduced IAC by 92 +/- 4.7%. Inhibition of IAC by ACTH, 8-pcpt-cAMP and forskolin was not prevented by the cAMP-dependent protein kinase inhibitors H-89 (5 microM), cAMP-dependent protein kinase inhibitor peptide (PKI[5-24]) (2 microM), (Rp)-cAMPS (500 microM), or by the nonspecific protein kinase inhibitor staurosporine (100 nM) applied externally or intracellularly through the patch pipette. At the same concentrations, these kinase inhibitors abolished 8-pcpt-cAMP-stimulated A-kinase activity in AZF cell extracts. In intact AZF cells, 8-pcpt-cAMP activated A-kinase with an EC50 of 77 nM, a concentration 2,000-fold lower than that inhibiting IAC half maximally. The active catalytic subunit of A-kinase applied intracellularly through the recording pipette failed to alter functional expression of IAC. The inhibition of IAC by ACTH and 8-pcpt-cAMP was eliminated by substituting the nonhydrolyzable ATP analogue AMP-PNP for ATP in the pipette solution. Penfluridol, an antagonist of T-type Ca2+ channels inhibited 8-pcpt-cAMP-induced cortisol secretion with an IC50 of 0.33 microM, a concentration that effectively blocks Ca2+ channel in these cells. These results demonstrate that IAC is a K(+)-selective current whose gating is controlled by an unusual combination of metabolic factors and membrane voltage. IAC may be the first example of an ionic current that is inhibited by cAMP through an A-kinase-independent mechanism. The A-kinase-independent inhibition of IAC by ACTH and cAMP through a mechanism requiring ATP hydrolysis appears to be a unique form of channel modulation. These findings suggest a model for cortisol secretion wherein cAMP combines with two separate effectors to activate parallel steroidogenic signalling pathways. These include the traditional A-kinase-dependent signalling cascade and a novel pathway wherein cAMP binding to IAC K+ channels leads to membrane depolarization and Ca2+ entry. The simultaneous activation of A-kinase- and Ca(2+)-dependent pathways produces the full steroidogenic response.
Redox modulation of L-type calcium channels in ferret ventricular myocytes. Dual mechanism regulation by nitric oxide and S-nitrosothiols.
Authors: Campbell D L , Stamler J S , Strauss H C
Published: May 2004

The effects of NO-related activity and cellular thiol redox state on basal L-type calcium current, ICa,L, in ferret right ventricular myocytes were studied using the patch clamp technique. SIN-1, which generates both NO. and O2-, either inhibited or stimulated ICa,L. In the presence of superoxide dismutase only inhibition was seen. 8-Br-cGMP also inhibited ICa,L, suggesting that the NO inhibition is cGMP-dependent. On the other hand, S-nitrosothiols (RSNOs), which donate NO+, stimulated ICa,L. RSNO effects were not dependent upon cell permeability, modulation of SR Ca2+ release, activation of kinases, inhibition of phosphatases, or alterations in cGMP levels. Similar activation of ICa,L by thiol oxidants, and reversal by thiol reductants, identifies an allosteric thiol-containing "redox switch" on the L-type calcium channel subunit complex by which NO/O2- and NO+ transfer can exert effects opposite to those produced by NO. In sum, our results suggest that: (a) both indirect (cGMP-dependent) and direct (S-nitrosylation/oxidation) regulation of ventricular ICa,L, and (b) sarcolemma thiol redox state may be an important determinant of ICa,L activity.
Vasoconstrictors inhibit ATP-sensitive K+ channels in arterial smooth muscle through protein kinase C.
Authors: Bonev A D , Nelson M T
Published: May 2004

The effects of vasoconstrictor-receptor (neuropeptide Y, alpha-adrenergic, serotonergic, histaminergic) stimulation on currents through ATP-sensitive potassium (KATP) channels in arterial smooth muscle cells were examined. Whole-cell KATP currents, activated by the synthetic KATP channel opener pinacidil or by the endogenous vasodilator, calcitonin gene-related peptide, which acts through protein kinase A, were measured in smooth muscle cells isolated from mesenteric arteries of rabbit. Stimulation of NPY-, alpha 1-, serotonin (5-HT2)-, and histamine (H1)-receptors inhibited KATP currents by 40-56%. The signal transduction pathway that links these receptors to KATP channels was investigated. An inhibitor of phospholipase C (D609) and of protein kinase C (GF 109203X) reduced the inhibitory effect of these vasoconstrictors on KATP currents from 40-56% to 11-23%. Activators of protein kinase C, a diacylglycerol analogue and phorbol 12-myristate 13-acetate (PMA), inhibited KATP currents by 87.3 and 84.2%, respectively. KATP currents, activated by calcitonin gene-related peptide, were also inhibited (47-87%) by serotonin, phenylephrine, and PMA. We propose that KATP channels in these arterial myocytes are subject to dual modulation by protein kinase C (inhibition) and protein kinase A (activation).
Surface Charges of K channels. Effects of strontium on five cloned channels expressed in Xenopus oocytes.
Authors: Elinder F , Madeja M , Arhem P
Published: May 2004

The effects of strontium (Sr2+; 7-50 mM) on five different cloned rat K channels (Kv1.1, Kv1.5, Kv1.6, Kv2.1, and Kv3.4), expressed in oocytes of Xenopus laevis, were investigated with a two-electrode voltage clamp technique. The main effect was a shift of the Gk(V) curve along the potential axis, different in size for the different channels. Kv1.1 was shifted most and Kv3.4 least, 21 and 8 mV, respectively, at 50 mM. The effect was interpreted in terms of screening of fixed surface charges. The estimated charge densities ranged from -0.37 (Kv1.1) to -0.11 (Kv3.4) e nm-2 and showed good correlation with the total net charge of the extracellularly located amino acid residues of the channel as well as with the charge of a specific region (the loop between the S5 segment and the pore forming segment). The estimated surface potentials were found to be linearly related to the activation midpoint potential, suggesting a functional role for the surface charges.
Purinergic receptor stimulation increases membrane trafficking in brown adipocytes.
Authors: Pappone P A , Lee S C
Published: May 2004

Stimulation of brown adipocytes by their sympathetic innervation plays a major role in body energy homeostasis by regulating the energy-wasting activity of the tissue. The norepinephrine released by sympathetic activity acts on adrenergic receptors to activate a variety of metabolic and membrane responses. Since sympathetic stimulation may also release vesicular ATP, we tested brown fat cells for ATP responses. We find that micromolar concentrations of extracellular ATP initiates profound changes in the membrane trafficking of brown adipocytes. ATP elicited substantial increases in total cell membrane capacitance, averaging approximately 30% over basal levels and occurring on a time scale of seconds to minutes. The membrane capacitance increase showed an agonist sensitivity of 2-methylthio-ATP > or = ATP > ADP > > adenosine, consistent with mediation by a P2r type purinergic receptor. Membrane capacitance increases were not seen when cytosolic calcium was increased by adrenergic stimulation, and capacitance responses to ATP were similar in the presence and absence of extracellular calcium. These results indicate that increases in cytosolic calcium alone do not mediate the membrane response to ATP. Photometric assessment of surface-accessible membrane using the dye FM1-43 showed that ATP caused an approximate doubling of the amount of membrane actively trafficking with the cell surface. The discrepancy in the magnitudes of the capacitance and fluorescence changes suggests that ATP both activates exocytosis and alters other aspects of membrane handling. These findings suggest that secretion, mobilization of membrane transporters, and/or surface membrane expression of receptors may be regulated in brown adipocytes by P2r purinergic receptor activity.
Heterogeneity of chloride channels in the apical membrane of isolated mitochondria-rich cells from toad skin.
Authors: Sørensen J B , Larsen E H
Published: May 2004

The isolated epithelium of toad skin was disintegrated into single cells by treatment with collagenase and trypsine. Chloride channels of cell-attached and excised inside-out apical membrane-patches of mitochondria-rich cells were studied by the patch-clamp technique. The major population of Cl- channels constituted small 7-pS linear channels in symmetrical solutions (125 mM Cl-). In cell-attached and inside-out patches the single channel i/V-relationship could be described by electrodiffusion of Cl- with a Goldmann-Hodgkin-Katz permeability of, PCl = 1.2 x 10(-14) - 2.6 x 10(-14) cm3. s-1. The channel exhibited voltage-independent activity and could be activated by cAMP. This channel is a likely candidate for mediating the well known cAMP-induced transepithelial Cl- conductance of the amphibian skin epithelium. Another population of Cl- channels exhibited large, highly variable conductances (upper limit conductances, 150-550 pS) and could be activated by membrane depolarization. A group of intermediate-sized Cl(-)-channels included: (a) channels (mean conductance, 30 pS) with linear or slightly outwardly rectifying i/V-relationships and activity occurring in distinct "bursts," (b) channels (conductance-range, 10-27 pS) with marked depolarization-induced activity, and (c) channels with unresolvable kinetics. The variance of current fluctuations of such "noisy" patches exhibited a minimum close to the equilibrium-potential for Cl-. With channels occurring in only 38% of sealed patches and an even lower frequency of voltage-activated channels, the chloride conductance of the apical membrane of mitochondria-rich cells did not match quantitatively that previously estimated from macroscopic Ussing-chamber experiments. From a qualitative point of view, however, we have succeeded in demonstrating the existence of Cl-channels in the apical membrane with features comparable to macroscopic predictions, i.e., activation of channel gating by cAMP and, in a few patches, also by membrane depolarization.
A quinine-activated cationic conductance in vertebrate taste receptor cells.
Authors: Tsunenari T , Hayashi Y , Orita M , Kurahashi T , Kaneko A , Mori T
Published: May 2004

The chincona alkaloid quinine is known to be a bitter tasting substance for various vertebrates. We examined the effects of quinine on isolated taste receptor cells from the bullfrog (Rana catesbeiana). Membrane currents were recorded by whole-cell recording, while quinine hydrochloride was applied extracellularly from a puffer pipette. At the resting potential (-77 +/- 9 mV, mean +/- SD, n = 49 cells), taste cells generated inward currents in response to quinine stimulation (> 1 mM), indicating a depolarizing response in the taste cells. Two types of current responses were observed; a newly found quinine-activated cationic conductance and a previously reported blocking effect of quinine on K+ conductances. The cationic current was isolated from the K+ current by using a Cs(+)-containing patch pipette. The relative permeabilities (Pion) of the quinine-activated cationic conductance were: PNa/PK/PCs = 1:0.5:0.42. The quinine dose-response relation was described by the Hill equation with the K1/2 of 3.6 mM and Hill coefficient of 5.3. When extracellular [Ca2+] (1.8 mM) was reduced to nominally free, the conductance was enhanced by about sixfold. This property is consistent with observations on quinine responses recorded from the gustatory nerve, in vivo. The quinine-induced cationic current was decreased with an application of 8-bromo-cAMP. We conclude that the bitter substance quinine activates a cation channel in taste receptor cells and this channel plays an important role in bitter taste transduction.
The asymmetry of chloride transport at 38 degrees C in human red blood cell membranes.
Authors: Knauf P A , Gasbjerg P K , Brahm J
Published: May 2004

Band 3-mediated Cl- exchange in human red blood cells and resealed ghosts was measured at 38 degrees C by the continuous flow tube method. When external Cl- concentration, C(o), is varied with constant internal Cl- concentration, C(i), the flux fits a simple Michaelis-Menten saturation curve (MM fit), with K1/2o = 3.8 +/- 0.4 mM. When the Cl- concentration is varied simultaneously at both sides of the membrane in resealed ghosts (C(i) = C(o) = C(i = o)), the flux rises toward a flat maximum between 200 and 450 mM Cl-, and then decreases at very high C(i = o). An MM fit to the data with C(i = o) < 500 mM gives K1/2s of 106 +/- 13 mM; fits including modifier site inhibition (MS fit) give an over threefold higher K1/2s. Despite this uncertainty, the intrinsic asymmetry of unloaded transport sites, A (defined as E(o)/E(i) with C(i) = C(o), where E(i) is the fraction of unloaded inward-facing sites and E(o) is the fraction of unloaded outward-facing sites), calculated from K1/2s and K1/2o, ranges only from 0.046 to 0.107. A new method, which uses the initial slope of a plot of Cl- flux versus C(i = o), gives A values of 0.023 to 0.038. Flufenamic acid (FA) inhibits Cl- exchange by binding to an external site different from the transport site. At 38 degrees C, FA binds 24-36 times more tightly to E(o) than to E(i). Estimates of A from FA inhibitory potency range from 0.01 to 0.05. All methods, including bicarbonate data from the preceding paper, indicate that at 38 degrees C, like 0 degree C, far more band 3 molecules are in the E(i) than in the E(o) form. The agreement of various methods supports the ping-pong model for anion exchange, and demonstrates that the intrinsic asymmetry is very slightly, if at all, affected by temperature.
ACID PENETRATION INTO LIVING TISSUES
Authors: Taylor Nelson W.
Published: May 2004

The threshold concentrations for sourness of nine acids have been determined with an accuracy of about 8 per cent, and the H+ ion concentration of these acids measured.

Calculations have been made of the relative concentration gradients of the undissociated acid across the cell membrane for a series of acids having equal sourness and also for a series of acids having equal penetration velocity as determined from experiments by Crozier on Chromodoris and on Allolobophora. For solutions of equal pH a high degree of sourness has been found to be associated with a high penetration velocity of the undissociated acid or of the anion. A comparison of these gradients with the results of adsorption experiments on charcoal indicates that the acids are taken into the tissues by an adsorption process.

Polar groups such as OH and Cl and Br are found to have a very marked effect in reducing the ability of organic acids to penetrate living tissues.

The important rôle of optical activity of the acids in determining their physiological action has been noted.
THE MEASUREMENT OF GALVANOTROPIC EXCITATION
Authors: Crozier W. J. , Stier T. J. B.
Published: May 2004

The expression of galvanotropic excitation in energy units is obtained by the measurement of the current densities required to balance phototropic excitation (or reciprocally). With the triclad Leptoplana preliminary measurements show that the current is proportional to the logarithm of the light intensity.
THE DECOMPOSITION OF HYDROGEN PEROXIDE BY LIVER CATALASE
Authors: Williams John
Published: May 2004

1. The velocity of decomposition of hydrogen peroxide by catalase as a function of (a) concentration of catalase, (b) concentration of hydrogen peroxide, (c) hydrogen ion concentration, (d) temperature has been studied in an attempt to correlate these variables as far as possible. It is concluded that the reaction involves primarily adsorption of hydrogen peroxide at the catalase surface.

2. The decomposition of hydrogen peroxide by catalase is regarded as involving two reactions, namely, the catalytic decomposition of hydrogen peroxide, which is a maximum at the optimum pH 6.8 to 7.0, and the "induced inactivation" of catalase by the "nascent" oxygen produced by the hydrogen peroxide and still adhering to the catalase surface. This differs from the more generally accepted view, namely that the induced inactivation is due to the H2O2 itself. On the basis of the above view, a new interpretation is given to the equation of Yamasaki and the connection between the equations of Yamasaki and of Northrop is pointed out. It is shown that the velocity of induced inactivation is a minimum at the pH which is optimal for the decomposition of hydrogen peroxide.

3. The critical increment of the catalytic decomposition of hydrogen peroxide by catalase is of the order 3000 calories. The critical increment of induced inactivation is low in dilute hydrogen peroxide solutions but increases to a value of 30,000 calories in concentrated solutions of peroxide.
THE ACTION OF POTASSIUM CYANIDE AND POTASSIUM FERRICYANIDE ON CERTAIN RESPIRATORY PIGMENTS
Authors: Cook S. F.
Published: May 2004

The oxygen in hemoglobin is liberated by K3Fe(CN)6 and not by KCN, that in hemocyanin by KCN and not by K3Fe(CN)6, that in hemerythrin by both, and that in echinochrome by K3Fe(CN)6 and not by KCN. The bearing of these results on the nature of the substances involved is discussed.
THE PHOSPHATE ION AND HYDROLYSIS BY PANCREATIC LIPASE
Authors: Dawson E. R. , Platt B. S.
Published: May 2004

The equation, (activity of enzyme) (pPO4)n = K, has been investigated and has been shown to have only a limited application to the effect of the phosphate ion on the hydrolytic activity of pancreatic lipase. The deviations observed are ascribed to the effect of certain factors on the stability of the enzyme.
TEMPERATURE CHARACTERISTICS FOR THE GROWTH OF THE SPORANGIOPHORES OF PHYCOMYCES
Authors: Castle E. S.
Published: May 2004

1. With constant temperature and light intensity, the rate of elongation of a sporangiophore of Phycomyces is constant for many hours.

2. With constant light intensity, values of µ, the "critical thermal increment," have been computed for the elongation of different sporangiophores. These values group themselves closely about the modes 11,000, 16,000, 20,000, 26,000, and 33,000 calories. Sporangiophores from the same culture need not have similar increments.

3. The significance of these results for studies of growth is discussed.
THE EFFECT OF TEMPERATURE ON THE MECHANICAL ACTIVITY OF THE GILLS OF THE OYSTER (OSTREA VIRGINICA Gm.)
Authors: Galtsoff Paul S.
Published: May 2004

1. The method is described whereby the rate of flow produced by the gills of the oyster can be measured accurately.

2. The rate of doing work in maintaining a constant current along the glass tube can be expressed by the formula W = 2πlµ S2, where W = ergs/sec., l = length of the tube, µ = viscosity in poises, and S = speed at the axis of the tube.

3. The relationship between the rate of doing work and the temperature cannot be described by the equation of Arrhenius.

4. The optimum temperature for the mechanical activity of the gills lies between 25° and 30°C. Below 5° no current is produced, though the cilia are beating. Ciliary motion stops entirely at the freezing temperature of sea water.

5. The factors responsible for the production of current are discussed. The study of the relations between the variability of the rate of flow and the temperature shows that between 15° and 25°C. the absolute variability remains constant and increases considerably above 25° and below 15°. The rôle of the coordination in the production of current is discussed, and the conclusion is reached that coordination is affected by the changes in temperature.
THE OXYGEN CONSUMPTION OF LUMINOUS BACTERIA
Authors: Harvey E. Newton
Published: May 2004

Oxygen consumption of luminous bacteria determined by the Thunberg micro respirometer and by the time which elapses before the luminescence of an emulsion of luminous bacteria in sea water begins to dim, when over 99 per cent of the dissolved oxygen has been consumed, agree exactly.

Average values for oxygen consumption at an average temperature of 21.5°C. are 4.26 x 10–11 mg. O2 per bacterium; 2.5 x 104 mg. per kilo and 5.6 mg. O2 per sq. m. of bacterial surface.

The only correct comparison of the oxygen consumption of different organisms or tissues is in terms of oxygen used per unit weight with a sufficient oxygen tension so that oxygen consumption is independent of oxygen tension.

Measurement of the oxygen concentration which just allows full luminescence, compared with a calculation of the oxygen concentration at the surface of a bacterial cell just necessary to allow the observed respiration throughout all parts of the cell, indicates that oxygen must diffuse into the bacterium much more slowly than through gelatin or connective tissue but not as slowly as through chitin.
COMBINATION OF SALTS AND PROTEINS
Authors: Northrop John H. , Kunitz M.
Published: May 2004

1. The combination of Cu++, Ca++, Mg++, Al+++, La+++, K+, Ag+, and Cl- with gelatin has been determined.

2. The equivalent combining value for copper is about 0.9 millimols per gm. of gelatin and is therefore the same as that of hydrogen. The value for copper with deaminized gelatin is about 0.4 to 0.5, again the same as that of hydrogen. The sum of the hydrogen and copper ions combined in the presence of an excess of either is 0.9 millimols showing that there is an equilibrium between the copper hydrogen and gelatin and that the copper and hydrogen are attached to the same group.

3. The equivalent combining value of La+++ and Al+++ is about 0.5 millimols per gm. of gelatin. This value is not significantly different with deaminized gelatin so that it is possible these salts combine only with groups not affected by deaminization.

4. No calcium is combined on the acid side of pH 3. The value rises rapidly from pH 3 to 4.7 and then remains constant.

5. No combination of K, Li, Na, NO3 or SO4 could be detected.

6. Cl combines less than the di- and trivalent metals so that the protein is positive in CaCl2 but negative in KCl.
DRUG ACTION IN GALVANOTROPIC RESPONSES
Authors: Fries E. F. B.
Published: May 2004

Under strychninization involving reversal of reciprocal inhibition of the circular and longitudinal muscles, planarians and earthworms show reversed, i.e., anodal, galvanotropic responses, which neither nicotine nor atropine induce (in planarians). The results strengthen the conclusion (Crozier, 1926–27) that in causing reversal of inhibition strychnine acts primarily on central synapses or on homologous elements.

Like other arthropods, on the other hand, Asellus is little affected by strychnine; no reversal occurs. Caffeine and atropine are even less effective. Nicotine evokes abnormal posture and movements, perhaps reversed, but no alteration of anodal galvanotropism.
THE ANTAGONISM BETWEEN ACETIC ACID AND THE CHLORIDES OF SODIUM, POTASSIUM, AND CALCIUM AS MANIFESTED IN DEVELOPING FUNDULUS EMBRYOS
Authors: Armstrong Philip B.
Published: May 2004

1. Developing Fundulus embryos react in much the same way to mixtures of acetic acid in salt solutions whether their membranes are removed or not. It is therefore not necessary to assume any specific rôle for the membrane.

2. The primary toxic effect of acetic acid is to kill the surface of the embryo; heart stoppage is due to penetration of the acid after the surface has been injured.

3. The salt (NaCl, KCl, CaCl2) antagonizes the acetic acid by slowing or preventing the killing of the surface of the embryo.

4. If embryos are immersed in certain KCl-acetic acid mixtures, the surface killing effect of the acid is antagonized but at the same time the KCl penetrates and stops the heart in the manner which is characteristic of a KCl solution alone.
THE IONIC ACTIVITY OF GELATIN
Authors: Simms Henry S.
Published: May 2004

2.5 and 1.25 per cent gelatin have been titrated potentiometrically in the absence of salts and in the presence of two concentrations (0.0750 and 0.0375µ) of NaCl, MgCl2, K2SO4, and MgSO4. The data have been used to calculate values of ± S = vz – (v – 1)z, where vz = v2 – (v2 – v) rx/18.

The maximum and minimum values of S with NaCl were used to calculate the mean distance (rx) between like charges in gelatin. This is found to be 18 Å.u. or over (between acid or basic groups) which agrees with the probable value and the titration index dispersion. Thus the data with NaCl are shown to be normal and to obey the equation found to hold for simple weak electrolytes; namely, pK' – pK = Sa

See PDF for Equation

where S is related to the valence and distance by the above equations.

Using the NaCl data as a standard the deviations (ΔS) produced by the other salts are calculated and are found to agree quantitatively with the deviations calculated from equations derived for the simple weak electrolytes. This shows that in gelatin, as in the simple electrolytes, the deviations are related to the "apparent valences" (values which are a function of the true valence and the distance between the groups).

The maximum "apparent valences" of gelatin are 2.4 for acid groups (in alkaline solution) and 1.8 for basic groups (in acid solution). These values correspond to the hypothetical condition of zero distance between the groups. They have no physical significance but have a practical utility first as mentioned above, and second in that they may be used in the unmodified Debye-Hückel equation to give the maximum effect of gelatin on the ionic strength. The true effect is probably even lower than these values would indicate.

The data indicate that gelatin is a weak polyvalent ampholyte having distant groups and that the molecule has an arborescent structure with interstices permeated by molecules of the solvent and other solutes. The size and shape probably vary with the pH.
DIALYSIS WITH STIRRING
Authors: Kunitz M. , Simms H. S.
Published: May 2004

Substances to be purified by dialysis are placed in collodion bags together with a toy "marble" or a bubble of air. The bags are stoppered and placed in glass tubes of a rocking machine. Distilled water of the desired temperature is circulated through the tubes (around the bags) at a rate of about 8 cc. per minute per bag while the machine is in motion. The rolling of the marbles or bubbles causes stirring which makes it possible to remove the salts from a protein solution in 24 to 48 hours.
GEOTROPIC ORIENTATION IN ARTHROPODS
Authors: Crozier W. J. , Stier T. J. B.
Published: May 2004

The geotropic orientation of caterpillars of Malacosoma americana during progression upon a surface inclined at angle α to the horizontal is such that the path makes an average angle θ upward on the plane, of a magnitude proportional to log sin α. More precisely, the product (sin α) (sin θ) is constant. This is traced to the fluctuation of the pull of the head region upon the lateral musculature of the upper side during the side to side swinging implicated in progression.
THE SALTING OUT OF GELATIN INTO TWO LIQUID LAYERS WITH SODIUM CHLORIDE AND OTHER SALTS
Authors: McBain James W. , Kellogg Frederick
Published: May 2004

1. Conditions under which gelatin may be salted out into two liquid layers at 35° were studied.

2. The equilibria governing the amounts and composition of the layers salted out with sodium chloride are found to accord with the requirements of the phase rule for the quaternary system gelatin-sodium chloride-hydrogen ion-water.

3. So far, soaps and gelatin are found to be surprisingly similar in their behaviour and definite indications are given as to where further similarities may be sought.

4. It is evident from this work that the term "coagulation" as ordinarily applied to the salting out of proteins is definitely a misnomer.
EFFECTS OF CYANIDE ON THE PROTOPLASM OF AMEBA
Authors: Brinley Floyd J.
Published: May 2004

The experiments seem to indicate that the toxicity of HCN and KCN for amebæ is due to their effect on the cell membrane and not on the internal protoplasm.

Concentrated solutions (N/10–N/300) of HCN or KCN produce an initial increase in viscosity of the protoplasm of amebæ (immersed) which is followed by liquefaction and disintegration of the cell. Dilute solutions of HCN or KCN decrease the viscosity of the protoplasm of amebæ.

Injections of HCN or KCN into amebæ produce a reversible decrease in viscosity of the protoplasm.
THE INJECTION OF SULFATES INTO VALONIA
Authors: Blinks L. R.
Published: May 2004

Potassium chloride and sulfate were injected into the vacuole of Valonia. The surviving cells tolerated the presence of these solutions. Sulfate, although ordinarily absent from the sap, is not rapidly eliminated when introduced. Hence the sulfate occasionally found in cells of normal appearance may have entered due to temporary injury followed by recovery.
INTERNAL VERSUS EXTERNAL TOXICITY IN VALONIA
Authors: Jacques A. G. , Osterhout W. J. V.
Published: May 2004

When MnCl2 is injected into the cells of Valonia macrophysa they live only about half as long as when the same concentration is applied to the exterior of the cell. This is due to toxic action and not to the mechanical disturbance accompanying the injection (since all cells were stabbed in the same manner by the capillary).

A variety of explanations are suggested, all of which involve a difference between the inner and outer layers of the protoplasm.
CHEMICAL ANTAGONISM OF IONS
Authors: Simms Henry S.
Published: May 2004

Sulfate ions (SO4=) produce an anomalous effect on the ionization of oxalate diion, opposite in direction to the effect of Mg++ ions. This effect of sulfate is antagonized by the presence of Cl- ions according to the equation:

See PDF for Equation

where f' is the antilog of the increase in pK2' due to the sulfate.

In solutions containing up to 0.03 molar MgSO4 the effect of Mg++ predominates over that of SO4=. Above 0.1 molar the effect of SO4= predominates and tends to neutralize the initial deviation.

In solutions containing fixed amounts of MgCl2 and varying amounts of NaSO4 (or vice versa) the effects of these two salts sharply antagonize each other in all proportions.
THE EFFECT OF THE HYDROGEN ION CONCENTRATION ON THE RATE OF HYDROLYSIS OF GLYCYL GLYCINE, GLYCYL LEUCINE, GLYCYL ALANINE, GLYCYL ASPARAGINE, GLYCYL ASPARTIC ACID, AND BIURET BASE BY EREPSIN
Authors: Northrop John H. , Simms Henry S.
Published: May 2004

1. The rate of hydrolysis at different pH values of glycyl glycine, glycyl leucine, glycyl alanine, glycyl asparagine, glycyl aspartic acid and biuret base has been determined.

2. The pH-activity curves obtained in this way differ for the different substrates.

3. The curves can be satisfactorily predicted by the assumption that erepsin is a weak acid or base with a dissociation constant of 10–7.6 and that the reaction takes place between a particular ionic species of the enzyme and of the substrate. There are several possible arrangements which will predict the experimental results.

4. The rate of inactivation of erepsin at various pH values has been determined and found to agree with the assumption used above, that the enzyme is a weak acid or base with a dissociation constant of about 10–7.6.

5. It is pointed out that if the mechanism assumed is correct, the determination of a significant value for the relative rate of hydrolysis of various peptides is a very uncertain procedure.
THE NATURE OF THE FACTORS WHICH DETERMINE THE SEQUENCE OF GROWTH-CYCLES AND ITS RELATIONSHIP TO THE DIFFERENTIATION OF TISSUES
Authors: Robertson T. Brailsford
Published: May 2004

1. It has previously been shown by the author and many others that growth, in animals and plants, is an autocatalysed process. In animals it is usual to find that growth occurs in several superimposed autocatalytic cycles. In many cases, in plants and animals, especially if the cycle is one which occupies a large proportion of the growing period, it is found that the velocity-constant of the autocatalysed monomolecular formula falls off as growth proceeds, at first rapidly and later more slowly.

2. It has previously been shown by the author that the fall of the velocity-constant of growth, in the white mouse, is directly proportional to the fall of the nucleo-cytoplasmic ratio, determined by the chemical method of Le Breton and Schaeffer. If we assume this relationship to be generally applicable to the growth of animals and plants, then the following additional conclusions may be deduced, without calling in the aid of any other assumption:—

3. The increase of cytoplasm in any given cycle of growth is proportional to the concurrent increase of nuclear material.

4. The growth of cytoplasm takes place in accordance with a monomolecular formula in which the velocity-constant varies directly as the mass of the nucleus.

If we superadd to these facts and deductions the hypothesis that each growth-cycle represents the growth of a separate group of cells within the animal, then the additional conclusions follow:—

5. That the cells which participate in the growth composing any cycle have initially lower nucleo-cytoplasmic ratios than the cells which participated in the preceding cycles.

6. That cells of large nucleo-cytoplasmic ratios in a multicellular animal inhibit the growth of cells which possess smaller ratios.

7. These conclusions collectively imply that the nucleus plays a predominant role in determining the development of the cell in which it resides.