bluuebunny/crossref_metadata_2025 huggingface dataset:
Stratum corneum of frog skin: inferences for studies of Na entry and transport pool
Authors: Helman S. I. , Fisher R. S.
Published: December 2017

Pieces of isolated stratum corneum from frog skins were studied. Preliminary data showed that approximately 56% of the total sodium of split skins was associated with the stratum corneum. In more detailed studies, the sodium space estimated with 22Na and the volume of tissue water were identical, averaging 0.95 mul/cm2. Thus, the stratum corneum contained approximately 0.11 mueq Na+/cm2. Similar determinations of the sucrose, mannitol, and inulin spaces of the stratum corneum gave mean values of 0.84, 2.21, and 1.84 mul/cm2, respectively. Surprisingly, the mannitol and inulin spaces were observed to be at least twice as large as the space occupied by the tissue water, and this can be interpreted to mean that mannitol and inulin bind in appreciable amounts and thus are unsuitable markers of the sodium space. Whereas the kinetics of sodium uptake and washout could be described simply, similar studies for sucrose, mannitol, and inulin were more complex and consistent with appreciable binding of the substances to the stratum corneum.
Detection of contraction of isolated smooth muscle cells in suspension
Authors: Singer J. J. , Fay F. S.
Published: December 2017

A Coulter counter has been utilized to assess the contractile state of suspensions of isolated smooth muscle cells prepared by enzymatic digestion of stomach muscularis of Bufo marinus. Pulse-duration and pulse-hieght histograms were constructed from the pulses that occur as cells pass through the Coulter counter orifice. Contraction of cells in suspension causes shifts in these pulse histograms to a greater percent of shorter duration pulses and of larger pulse heights. These shifts are consistent with teh assumption made in out studies that the duration and amplitude of the pulses generated are related to the length and cross-sectional area (or square of the diameter), respectively, of the cell. Shifts in the pulse-height histogram were found to be more reliable. The results of a calibration experiment in which shifts in the histograms of pulse heights were linerrly related to shifts in the histograms of all lengths measured from photomicrographs suggested that the shifts in the pulse-height histogram could be used as a continuous index of changes in the contractile state of a population of cells in suspension.
Neurotrophic regulation of insulin-sensitive amino acid uptake in rat fast muscle
Authors: Robbins N. , Lyle P. D.
Published: December 2017

Our object was to determine how innervation regulates muscle insulin sensitivity. Insulin-stimulated uptake of the nonmetabolized amino acid, 2-amino-isobutyric acid, was used as a measure of insulin sensitivity in denervated rat extensor digitorum longus muscles retaining either a similar 2.5-cm (““proximal denervation”) or a similar to 0.5-cm (““distal denervation”) length of distal nerve stump. Because both muscles were inactive in the first 24 h, any difference in insulin sensitivity could be due only to some trophic influence of the distal nerve stump. Fifteen hours after either type of denervation, 2-aminoisobutyric acid uptake was refractory to insulin. However, at 24 h, insulin sensitivity of distally denervated muscles (with or without a second ipsilateral proximal denervation) was normal, whereas that of proximally denervated muscles was still relatively insensitive. In the absence of insulin, the two types of denervated muscles at 24 h showed no difference in 2-aminoisobutyric acid uptake. Finally, organ culture of paired muscles with or without long nerve stumps showed corresponding differences in insulin-stimulated 2-aminoisobutyric acid uptake after 48 h in vitro. Thus, a neurotrophic factor, independent of impulse activity, stretch, or changes in blood flow, regulates one type of muscle insulin sensitivity.
Physiological characteristics of skeletal muscles of dogs and cats
Authors: Maxwell L. C. , Barclay J. K. , Mohrman D. E. , Faulkner J. A.
Published: December 2017

Our purpose was to determine if physiological characteristics of skeletal muscles of dogs and cats are related to their histochemical and biochemical characteristics. Maximum oxygen consumption (VO2max) and blood flow (Q) at VO2max were determined for in situ muscles of dogs and cats. Compared to cat muscles, dog muscles per unit mass had higher succinate oxidase activities, VO2max's, and Q's at VO2max's. There are positive relationships between Q at VO2max and VO2max and between VO2max and succinate oxidase activity. The higher VO2max's and succinate oxidase activities of dog muscles are consistent with the presence in these muscles of only slow-twitch fatique-resistant fibers and fast-twitch fatique-resistant fibers, whereas up to 50% of the fibers found in cat muscles are fast-twitch fatiqable. Capillary-to-fiber ratios are 2.40-2.97 for dog muscles compared to 2.17-2.84 for cat muscles. Thus the two- to threefold higher Q at VO2max for dog muscles compared to cat muscles is not due to a greater number of capillaries.
Application of a solid membrane ion-selective electrode to in vivo measurements
Authors: Crowe W. , Mayevsky A. , Mela L.
Published: December 2017

A solid membrane electrode containing a highly selective ion-complexing agent immobilized in a polymer membrane is applied to measurements in vivo from the surface of an organ. For the measurements reported here, an ion-complexing agent selective for potassium is incorporated in a silicone rubber membrane and applied to measure ion changes in the brain. Comparison is made to the measurements recorded with an ion-selective microelectrode in the cortical tissue. The surface electrode compares favorably with the microelectrode in terms of amplitude of response and response time for the changes seen in the phenomenon of cortical spreading depression of Leao. The methods reported here are amenable to a selection of ion measurements by incorporation of a suitable ion exchanger in a polymer membrane. Extracellular ion activity is monitored in the anesthetized animal by holding the electrode in a balanced suspension which provides a light, flexible contact to the organ of interest. In the unanesthetized animal, when recording from the brain, the electrode is fixed in a skull-implanted cannula.
Somatostatin inhibition of glucose-induced electrical activity in cultured rat islet cells
Authors: Pace Caroline S. , Murphy Mary , Conant Susan , Lacy Paul E.
Published: December 2017

Electrophysiological studies of rat islet cells in monolayer culture were undertaken to determine the role of transmembranous ionic fluxes in the inhibitory action of somatostatin on insulin release. In the presence of somatotropin release inhibiting factor (SRIF) (2.5 nM), hyperpolarization occured with or without glucose (16.6 mM) in the medium. SRIF also inhibited the incidence of glucose-induced spike activity. The inhibitory action of SRIF occurred within 5 min and was readily reversible. An increase in extracellular K+ (5–13 mM) or Ca2+ (2.3–4.6 mM) prevented SRIF inhibition of glucose-induced electrical activity. The secretory response of cultured islets to glucose (16.6 mM) was completely inhibited by SRIF (2.5 nM). The presence of high [Ca2+]0 or [K+]0, enhanced insulin release in the presence of SRIF and glucose. Although phentolamine (5.0 μg/ml) did not block the inhibition of glucose-induced electrical responses by SRIF, it prevented the inhibitory action of epinephrine (0.2 μg/ml). It is concluded that the primary action of SRIF is to alter transmembranous cationic fluxes, as manifested by hyperpolarization and a decrease in the incidence of spike activity, which may prevent glucose from eliciting a normal secretory response.

insulin secretion; epinephrine; alpha-adrenergic blockade; stimulus-secretion coupling

Submitted on February 14, 1977
High sensitivity of cultured cardiac muscle cells to autonomic agents
Authors: Hermsmeyer K. , Robinson R. B.
Published: December 2017

We have established conditions under which cultured embryonic myocardial cells are highly sensitive to the autonomic agents norepinephrine and acetylcholine and have determined that the most important factors affecting this sensitivity involve the application protocol. Using cells 3-5 days in culture, isolated from ventricles of 13-day chick embryos, the ED50 for noerpinephrine was 800 pM and that for acetylcholine was 370 pM. These cells were more than 2 orders of magnitude more sensitive than 13-day embryonic hearts freshly isolated, but not dispersed. Intracellular recording of the membrane actions of norepinephrine and acetylcholine on these cultured cells showed changes in pacemaker slope similar to those seen in freshly isolated hearts. These data demonstrate that preparation of ventricular muscle as isolated cells in culture does not necessarily result in the loss of sensitivity to autonomic agents. On the contrary, the isolated cells show the highest sensitivity to norepinephrine and acetylcholine that has been reported for the myocardium.
Pulmonary absorption of drugs in the neonatal rat
Authors: Hemberger J. A. , Schanker L. S.
Published: December 2017

To compare the pulmonary absorption of drugs in newborn rats (3-27 days old) with that in adults, 0.01-0.1 ml of Krebs-Ringer phosphate solution (pH 7.4) containing a drug was administered to anesthetized animals by way of a catheter introduced through a tight-fitting tracheal cannula. After various times, lungs and trachea were removed and assayed for drug that remained. Semilogarithmic plots of percent drug remaining against time yielded a straight line for each compound. The lipid-soluble drugs procaine amide and sulfisoxazole were absorbed at similar rates in newborn and adult rats. In contrast, the lipid-insoluble drugs tetraethylammonium, p-aminohippuric acid, and mannitol were absorbed approximately 2 times more rapidly in younger rats (3-12 days) than in older animals (18 day, 27 day, or adult). The results suggested that the respiratory tract membranes of 3- to 12-day-old rats have a greater porosity than those of older animals.
Invaginated membrane in crustacean tonic muscle fibers: estimates of membrane capacitance
Authors: Rossner K. L. , Sherman R. G.
Published: December 2017

Surface and volume densities of the invaginated membrane components of tonic muscle fibers of crayfish (Orconectes rusticus) were determined by stereological methods. Surface densities of the sarcolemma, sarcolemmal invaginations, T tubules and Z tubules were 2.0, 5.9, 26.3, and 3.3 micron2/100 micron3 of fiber, respectively, and volume densities of the sarcolemmal invaginations, T tubules, and Z tubules were 0.28, 0.29, and 0.08 micron3/100 micron3. The values obtained for surface density show that 95% of the membrane exposed to the extracellular environment is composed of invaginated membrane. Specific membrane capacitance, determined from square-wave pulse analysis and referred to the apparent area of surface sarcolemma, was 30.3 muF/cm2. However, after correction for the extent of invaginated membrane, the specific membrane capacitance was 1.6 muF/cm2.
Electron probe microanalysis of red blood cells. I. Methods and evaluation
Authors: Kirk R. G. , Bronner C. , Barba W. , Tosteson D. C.
Published: December 2017

The concentrations of potassium, sodium, and iron in human and sheep red blood cells were measured with an electron probe. Cells were prepared for analysis by spraying them on pyrolytic graphite supports. The results obtainedwith this spray technique agreed well with values measured on similar cells that were prepared for analysis by freezing, sectioning, and freeze-drying. Higher Na concentrations and lower K concentrations were found to be associated with lower cell volumes in human and high-potassium sheep cells. In low-potassium sheep cells the reverse was found, lower Na and higher K concentrations were associated with lower cell volumes. However, the amounts of iron were found to remain relatively constant in all human cells.
Electron probe microanalysis of red blood cells. II. Cation changes during maturation
Authors: Kirk R. G. , Lee P. , Tosteson D. C.
Published: December 2017

To understand the sequence of maturation of membrane transport and hemoglobin production during erythropoiesis, we have measured the K, Na, and Fe content in single mature red blood cells and bone marrow cells of dog using electron probe microanalysis (EPMA). Mature red blood cells of dog are low in potassium (LK) and high in sodium. These cells are derived from erythroblastic stem cells, which are high in potassium (HK) and low in sodium. This change from HK stem cells to LK red cells occurs in the marrow. The ratio of K/Na was found to be less than 0.2 independent of Fe/(K + Na) in circulating red cells. However, a significant number of marrow cells had both low K/Na and low Fe/(K + Na). We conclude that the changes in cation transport properties responsible for the conversion of HK to LK cells occur before the synthesis of hemoglobin in at least some marrow cells.
Uptake of unconjugated bilirubin by isolated rat hepatocytes
Authors: Iga T. , Eaton D. L. , Klaassen C. D.
Published: December 2017

The mechanism responsible for the hepatic uptake of unconjugated bilirubin was examined in isolated rat hepatocytes from control and phenobartital-pretreated rats. The uptake was extremely rapid and the equilibrium between cell and medium was attained within 60 s with a 100-fold higher concentration in the cell than the medium. The initial velocity of uptake (Vo) exhibited a linear relationship to the bilirubin concentration in the medium. Pretreatment of cells with various metabolic inhibitors had no effect on the uptake of unconjugated bilirubin. Ouabain did significantly decrease Vo, but replacement of sodium ion with choline or lithium had no effect on bilirubin uptake. The organic acids sulfobromophthalein (112 muM) and taurocholic acid (50 (muM) and two steroidal compounds, diethylstilbestrol (50 muM) and spironolactone (50 muM), had no effect on the uptake of bilirubin. It is suggested that bilirubin gains access to the hepatocyte interior by passive diffusion into and through the lipid membrane and that intracellular binding may explain the high degree of bilirubin accumulation associated with the isolated hepatocytes.
Localization of [3H]ouabain-sensitive Na+ pump sites in cultured pig kidney cells
Authors: Mills J. W. , Macknight A. D. , Dayer J. M. , Ausiello D. A.
Published: December 2017

Pig kidney cells, LLC-PK1, grown by standard tissue-culture techniques form monolayers and maintain morphological features characteristic of epithelia. Cultures exposed to 2 X 10(-6) M [3H]ouabain for 30 min at 37 degrees C bound 7.77 +/- 0.37 pmol/mg protein. This could be reduced by 58% by incubation in the presence of 45 mM K+. Freeze-dry radioautographic localization of [3H]ouabain-binding sites revealed grains distributed only along that fraction of the plasmalemma directly facing the culture-dish surface. Binding and localization of [3H]ouabain were correlated with an inhibition of the Na+ pump in these cells because analysis of cellular electrolytes in control cultures versus those exposed to 10(-3) M ouabain revealed a fall in K+ from 419 +/- 9 to 173 +/- 4 mmol/kg dry wt with a reciprocal increase in Na+. There was no change in cell H2O. Similarly, oxygen consumption was reduced by 32% after exposure to ouabain. These results provide direct evidence that in epithelial cells in culture the membrane facing the culture dish corresponds to the basolateral membrane of epithelial cells in vivo.
Lithium fluxes in human erythrocytes
Authors: Ehrlich B. E. , Diamond J. M.
Published: December 2017

The contribution of four transport pathways to Li+ influx and efflux in human erythrocytes was determined quantitatively, using Li+ concentrations comparable to those found in vivo when Li+ is used as treatment for manic-depressive illness. All pathways were measured simultaneously on each subject's blood sample to avoid possible temporal variations in transport parameters. We found that Li+ efflux is 75% via countertransport and 25% via a leak. The bicarbonate-sensitive pathway accounts for 30% of influx while the remaining 70% is via a leak. The Na+-K+ pump makes no significant contribution to Li+ influx or efflux under physiological conditions. Li+ efflux for a given [Li+]i is 3–5 times the Li+ influx for the same [Li+]o. However, due to interindividual variations in Na+-Li+ counter-transport, Li+ efflux but not influx varies considerably among individuals.
Depression, facilitation, and mobilization of transmitter at the rat diaphragm neuromuscular junction
Authors: Wilson D. F.
Published: December 2017

The characteristics of depression, facilitation, and mobilization of transmitter were examined at the rat diaphragm neuromuscular junction. Intracellular recording techniques were used to monitor end-plate potentials (EPPs), miniature end-plate potentials (MEPPs) and the muscle resting potentials. The cut-muscle technique was used to prevent muscle action potentials. Quantal release was determined by the direct method. The binomial statistical parameters, releasable store (n) and probability of release (p), were examined under various stimulating conditions to determine the basis for depression and facilitation. The present experiments demonstrate that p remains unchanged during repetitive nerve stimulation at low or moderately high frequencies. The experiments demonstrate that depression is due to a decrease in n and facilitation is due to an elevation in n. It is suggested that the increase in n during facilitation is due to a transient recruitment of inactive releasing sites. Substantial replenishment of n by mobilization occurs within a few ms after a stimulus but a slow residual rate of mobilization is needed to replenish n to resting levels.
Calcium transport and contractile activity in dissociated mammalian heart cells
Authors: Dani A. M. , Cittadini A. , Inesi G.
Published: December 2017

A homogeneous population of dissociated myocytes can be obtained by enzymic perfusion of adult rabbit hearts. The external membrane of the dissociated cells is freely permeable to electrolytes and is electrochemically shunted. Nevertheless, in the presence of 0.2--0.6 muM Ca2+, the myocytes undergo phasic contractions. Within the range of Ca2+ concentrations eliciting phasic contractions, the dissociated myocytes exhibit Ca2+ uptake activity that is sustained by endogenous ATP in the presence of oxygen and metabolites, or by hexogenous ATP in the presence of oligomycin and antimycin. The uptake is greatly enhanced by oxalate, an effect that is attributed to the activity of sarcoplasmic reticulum. Addition of the calcium ionophore A23187 prevents the occurrence of both Ca2+ accumulation and phasic contractions. In the presence of the ionophore the myocytes remain relaxed at Ca2+ concentrations (less than 1.0 mM) normally sustaining phasic contractile activity, and undergo irreversible contracture at Ca2+ concentrations (greater than 1.0 muM) sufficient to produce direct activation of the myofibrils. It is concluded that Ca2+ transport by sarcoplasmic reticulum is directly related to the occurrence of phasic contractions in dissociated myocytes prepared from rabbit heart. On the other hand, metabolic activity is required for ATP regeneration.
Reversible suppression of skeletal myotube formation in vitro obtained by varying [CO2]
Authors: Przybylski R. J. , Bullaro J. C. , MacBride R.
Published: December 2017

In primary cultures of chicken skeletal muscle, decreasing the [CO2] of the gaseous phase below 10(-3)% resulted in inhibition of cell proliferation and cytolysis. With 10(-3)% CO2-air, cell proliferation was slightly retarded and myotube formation was inhibited approximately 90% compared to cultures receiving 5% CO2-air. Changes in pH were not effective. Culture in low [CO2] resulted in the accumulation of lipoidal inclusions and unique cytoplasmic structures. Increasing time in culture with low [CO2] resulted in an increase in the length of G1 of the cell cycle. The inhibition was reversed by the addition of 5% CO2-air at any time in culture up to 2 wk with a minimum time of 3--6 h required. Lipoidal inclusions decreased in number and the unique cytoplasmic structures were absent. During the first 3 days in culture, myoblasts showing dependence on [CO2] for myotube formation increased in number, and the effect of elevated [CO2] on these cells was long lasting. The data suggest that some aspect of myoblast differentiation relating to cell recognition and fusion is affected by decreased [CO2].
Temperature- and Mg-ATP-dependent regulation of Ca2+ sensitivity of smooth muscle actomyosin ATPase
Authors: Bose R. , Hinton A. , King G. M.
Published: December 2017

Many smooth muscles on metabolic depletion undergo a contraction that is insensitive to EGTA [ethylene glycol-bis (beta-aminoethylether)N,N-tetraacetic acid]. Chicken gizzard actomyosin shows a progressive loss of Ca sensitivity accompanied by activation of EGTA-Mg-ATPase at temperatures near 37 degrees C with decreasing ATP concentrations. Ca2+-dependent phosphorylation still occurs under these conditions when the ATPase is Ca insensitive. Activation of EGTA-Mg-ATPase at low ATP concentration is not due to a pseudo-ATPase, or due to denautration of the actomyosin at 37 degrees C. Magnesium concentrations above 1 mM are required for observing the enhanced EGTA-Mg-ATPase activity and the Ca sensitivity is very markedly influenced by the magnesium concentrations of medium at low ATP. When the Mg-to-ATP ratio (5:1) was kept constant for varying ATP concentrations, activation of EGTA-ATPase was not observed. This activation was not due to the characteristics of the ATP regenerating system (phosphoenolpyruvate and pyruvate kinase) because with phosphocreatine and creatine phosphokinase similar results were obtained. Thus the EGTA-insensitive rise in tension during metabolic depletion is due to activation of Mg-ATPase and loss of Ca sensitivity at 37 degrees C, a temperature at which mammalian smooth muscles normally function.
Glyconeogenesis from lactate in frog striated muscle
Authors: Connett R. J.
Published: December 2017

The rates of 14carbon incorporation into CO2 and glycogen from [U-14C]-lactate and [1-14C]acetate in frog sartorius muscles were compared. The rates of incorporation into CO2 were similar, while the rate of incorporation of lactate into glycogen was more than 200-fold larger than that of acetate incorporation. It is concluded that the pathway of lactate incorporation into glycogen does not involve Krebs cycle intermediates and is extramitochondrial. To test the possibility that the pathway of lactate incorporation involves net reversal of a pyruvate kinase, the changes in phosphoenolpyruvate and pyruvate concentrations during stimulation of lactate incorporation into glycogen were measured. There wer none. The mass action ratio of pyruvate kinase was calculated. This value was two orders of magnitude from the equilibrium constant and it was concluded that reversal of pyruvate kinase was a very unlikely pathway. To test the possibility that a pathway involving the oxaloacetate-to-phosphoenolpyruvate step was involved the muscles were treated with 3-mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase. The treatment resulted in decreased incorporation of lactate into glycogen.
Force development of fast and slow skeletal muscle at different muscle lengths
Authors: Wallinga-de Jonge W. , Boom H. B. , Boon K. L. , Griep P. A. , Lammeree G. C.
Published: December 2017

It is known that the behavior of fast and slow skeletal muscles differs, but a comparison between fast and slow muscles with different stimulation patterns at various muscle lengths is lacking. The twitch, tetanus, and double pulse responses with a number of interval times have been investigated for a fast (EDL) and a slow (soleus) muscle of the rat at three muscle lengths (in vivo, at 37 degrees C, pentobarbital sodium anesthesia). The twitches of EDL and soleus change with muscle length, but the relative form of the ascending phase is independent of muscle length. The tetanus amplitude is independent of the muscle length over a considerable length range below the optimum twitch length. The form of the ascending phases of EDL-tetanus and double pulse responses (with certain interval times between the stimuli) varies with muscle length in contrast with the comparable soleus force patterns. The maximum slope in the descending phase of all contraction patterns decreases with increasing muscle length above the optimum twitch length.
Amino acid and hexose transport by cultured crypt cells from rat small intestine
Authors: Inui K. , Quaroni A. , Tillotson L. G. , Isselbacher K. J.
Published: December 2017

The characteristics of amino acid and sugar transport in intestinal crypt epithelial cells have been examined by measuring substrate uptake in an established epithelial cell line. These cells (IEC-6 cells) have been characterized as derived from rat small intestinal crypt cells on the basis of morphological criteria (J. Cell. Biol. 80: 248-265, 1979). Amino acid transport appeared to be mediated by both Na+-dependent and Na+-independent systems. Hexose uptake was stereospecific and Na+ independent, and was markedly inhibited by phloretin and cytochalasin B. Since glucocorticoids are known to have profound effects on maturation of the intestinal epithelium in vivo, their effects on transport properties of the cultured crypt cells were studied. Hydrocortisone, while completely inhibiting cell growth, increased the initial uptake rates of various hexoses, while having little or nor effect on the initial rate of amino acid uptake. The increased hexose uptake appeared to be due to a change in Vmax rather than Km. Appearance of the Na+-dependent hexose transport system, which is present in differentiated enterocytes, was not elicited by in vitro treatment with glucocortcoids.
Activation of fast skeletal muscle: contributions of studies on skinned fibers
Authors: Stephenson E. W.
Published: December 2017

The membrane potential of vertebrate twitch fibers closely controls Ca fluxes between intracellular compartments, which in turn control contraction. Recent work on intracellular Ca movement is reviewed in the general context of current efforts to synthesize physiological, biochemical, and structural observations on the contractile mechanism and its regulation, emphasizing the increasing role of functionally skinned fibers in this synthesis. Skinned fiber preparations, with removed or disrupted sarcolemma, bridge the gap between properties of isolated subsystems and their constrained operation in the intact fiber. Recent studies indicate that the surface action potential propagates along the transverse tubules, but not the sarcoplasmic reticulum (SR), which appears to be a distinct intracellular compartment. Voltage-dependent charge movements in the transverse tubules probably control Ca flux across the SR membranes. Current questions concern the mechanism of the signal that bridges the junctional gap between the two membrane systems, the mechanism and properties of the activated Ca efflux to the myofilament space, and the operation of the Ca pump of the SR during activation. New methods applied to intact fibers, cut fibers, skinned fibers, and subcellular systems are yielding the kind of information needed for a complete description of these central steps in excitation-contraction coupling and of Ca regulation of the myofilaments.
Potassium-stimulated 45Ca2+ uptake by subcellular particles of pancreatic beta-cells
Authors: Sehlin J.
Published: December 2017

Accumulation of 45Ca2+ by a microsomal fraction from pancreatic beta-cells of obese-hyperglycemic (ob/ob) mice was stimulated by Mg2+ in a concentration-dependent manner when 2 mM ATP was present. Maximum effect was reached at 2 mM Mg2+. Increasing the Na+ concentration from 20 to 115 mM had no significant effect, but K+ (10-123 mM) stimulated 45Ca2+ accumulation markedly when tested in the presence of 2 mM Mg2+. This effect was not due to changes of osmolarity, ionic strength, or the concentration of Cl-. Stimulation by K+ was drastically reduced on omission of Mg2+ from the incubation medium. K+ did not significantly affect 45Ca2+ uptake by a mitochondria-rich fraction of ob/ob mouse islets. It is suggested that K+ may be involved in modifying the subcellular distribution of calcium ions in pancreatic beta-cells.
Hormone effects on transport in cultured epithelia with high electrical resistance
Authors: Handler J. S. , Perkins F. M. , Johnson J. P.
Published: December 2017

Three continuous lines of amphibian epithelial cells form epithelia with a high transepithelial resistance (greater than 4,000 omega . cm2) in culture. The cell lines are TB-M and TB-6c, derived from the urinary bladder of Bufo marinus, and A6, derived from the kidney of Xenopus laevis. Short-circuit current is equivalent to net mucosa-to-serosa sodium transport in two cell lines and slightly exceeds sodium transport in epithelia formed by TB-6c cells. None of the cell lines has an adenylate cyclase response or a transport or permeability response to vasopressin. Water permeability is low in all three cell lines and is not affected by adenosine 3',5–-cyclic monophosphate (cAMP). In the three lines of cells, cAMP and aldosterone each increases short-circuit current with a time course similar to that seen in naturally occurring epithelia. In contrast to the toad urinary bladder and epithelia of line TB-M in which the aldosterone stimulation of short-circuit current is associated with a fall in transepithelial resistance, there is no change in resistance across epithelia of lines TB-6c and A6. There is also a striking difference in the sensitivity of the three lines to inhibition of short-circuit current by amiloride.
Growth and differentiated properties of a kidney epithelial cell line (MDCK)
Authors: Saier M. H.
Published: December 2017

The MDCK dog kidney epithelial cell line has been shown to retain the capacity for vectorial salt and fluid transport, sensitivity to growth regulation, and the ability to regenerate kidney tubular-like structures when injected into athymic nude mice. MDCK cells grown in tissue culture or in baby nude mice have the morphological properties of distal tubular cells, form tight and gap junctions, lack proximal tubular enzyme markers, and possess appreciable activities of Na+-K4-ATPase, ectoleucine aminopeptidase, and ectoalkaline phosphatase. Adenylate cyclase in intact cells is responsive to vasopressin, prostaglandins E1 and E2, and glucagon. Two Na+ transport systems have been characterized: a Na+-H+ antiport system, sensitive to amiloride inhibition, and a NaCl-KCl cotransport system, dependent on metabolic energy and sensitive to furosemide inhibition. Genetic techniques have been used to modify the properties of the cells. The results suggest that the MDCK cell line has retained the differentiated properties of the kidney epithelial cells of origin and that a clonally isolated cell possesses the receptor, transmission, and target enzyme systems necessary for the regulation of transcellular salt and fluid transport.
Dominance of longitudinal muscle in propagation of intestinal slow waves
Authors: Bortoff A. , Michaels D. , Mistretta P.
Published: December 2017

The purpose of these experiments was to test the hypothesis that circular muscle plays an active role in the propagation of intestinal slow waves, specifically be providing excitatory current through a process of regenerative amplification. With volume-recording techniques and microelectrode recordings we obtained the following results that are not consistent with such a mechanism: 1) slow waves propagated without delay or decrease in amplitude along segments of cat jejunum devoid of a ring of circular muscle up to 3 mm wide, i.e., across a longitudinal muscle bridge more than 4 space constants long (9 of 11 preparations) but did not propagate across a circumferential cut through the longitudinal muscle layer (14 of 14 preparations); 2) the membrane current associated with the slow wave had a pronounced inward component when recorded from either the serosal or the mucosal side of the longitudinal muscle bridge but was entirely outward when recorded from either the mucosal or the serosal side of exposed circular muscle, including those preparations in which various thicknesses of circular muscle were removed from the mucosal side of the recording area; 3) slow-wave amplitudes recorded intracellularly from intact (n = 9) and isolated (n = 8) longitudinal muscle preparations were not significantly different (27.0 +/- 4.3 vs. 25.4 +/- 5.3 (SD) mV); 4) after 30 min in 4.4 X 10(-6) M verapamil, slow-wave amplitude did not significantly decrease, although contractile activity had long since terminated. These results are more consistent with the hypothesis that longitudinal muscle provides most, if not all, of the current required for slow-wave propagation in the small intestine.
Intracellular chloride activity in rabbit papillary muscle: effect of ouabain
Authors: Caille J. P. , Ruiz-Ceretti E. , Schanne O. F.
Published: December 2017

Intracellular chloride activity (aiCl) and membrane potential (Vm) were measured in rabbit papillary muscle under in vitro conditions. The cellular chloride concentration (Cli) was estimated from measurements of total water content, extracellular space, and total chloride concentration. The effects of therapeutic (10(-8) M) and toxic (10(-6) M) concentrations of ouabain on these parameters were tested. The chloride-sensitive microelectrodes were of the liquid-ion exchanger type. Selectivity for HCO-3 was taken into account in the calculation of aiCl. In 11 control experiments made with two different protocols aiCl was determined in subendocardial and in deeper cells. The mean membrane potentials were -78.7 and -78.0 mV and the mean cytoplasmic chloride activities were 17.5 and 17.7 mM, respectively. The chloride equilibrium potentials were -43.5 and -43.2 mV. These results indicated that chloride is not passively distributed in rabbit papillary muscle. Ouabain (10(-8) M) did not change Vm or aiCl. At a toxic concentration of ouabain, Vm fell to -68.0 mV in superficial cells and to -67.8 mV in deeper cells, but aiCl remained unchanged . These results suggested that under in vitro conditions intracellular chloride is distributed within more than one cellular compartment.
Intracellular chloride activity in mammalian ventricular muscle
Authors: Baumgarten C. M. , Fozzard H. A.
Published: December 2017

The intracellular chloride activity (formula, see text) of quiescent rabbit right papillary muscle was measured with ion-selective microelectrodes (ISE) made with Corning 477315 liquid ion-exchange resin. The (formula, see text) was 9.8 +/- 2.4 (SD) mM, a value significantly greater than the 6.1 +/- 0.6 mM expected from passive distribution. The chloride equilibrium potential (ECl) was -64.4 +/- 6.6 mV, while membrane potential was -75.9 +/- 2.2 mV and significantly negative to ECl. These values are corrected for a nonchloride signal detected by the ISE. An apparent (formula, see text) of 4.8 +/- 0.6 mM was measured after exposure to Cl-free media for 1 h. Since isotopic chloride was totally washed out by this time, the apparent (formula, see text) in Cl-free media was interpreted as interference and subtracted from the (formula, see text) measured in other media. The conclusion that chloride is not passively distributed is supported by the observation that the (formula, see text) increase in high potassium media was smaller than predicted. In contrast to findings in papillary muscle, (formula, see text) of frog sartorius muscle was consistent with passive distribution, if it is assumed that interference was less than 0.5 mM.
Insulin does not hyperpolarize rat muscle by means of a ouabain-inhibitable process
Authors: Zierler K. , Rogus E.
Published: December 2017

Experiments were designed to test the hypothesis that insulin-induced hyperpolarization of rat skeletal muscle is mediated by stimulation of a ouabain-inhibitable electrogenic pump. Parallel experiments were carried out on rat caudofemoralis with isoproterenol, known to hyperpolarize rat skeletal muscle by stimulation of such a pump. Ouabain (10(-5) M) completely inhibited isoproterenol-induced hyperpolarization within 15 min but had no effect on half-maximal insulin-induced hyperpolarization. Ouabain (10(-6) M) inhibited isoproterenol effect by 60% during a period of 5–15 min. Ouabain (10(-4) M) had no effect on insulin-induced hyperpolarization within 10 min but depolarized during the next 10 min. In a separate series of studies in rat extensor digitorum longus muscle, 10(-5) M ouabain increased intracellular Na+ within 14 min. It is concluded that in rat caudofemoralis muscle, insulin-induced hyperpolarization is not mediated by a ouabain-inhibitable electrogenic pump.
Ion contents and other properties of isolated cells from dog tracheal epithelium
Authors: Widdicombe J. H. , Basbaum C. B. , Highland E.
Published: December 2017

We have developed a preparation of isolated cells from dog tracheal mucosa. The three major cell types of the intact epithelium (ciliated, secretory, and basal) are present in approximately the same proportions as in the intact tissue. These cells show high viability as judged by exclusion of vital dyes, high O2 consumption, and incorporation of amino acids into protein. The intracellular ion contents (in mmol/l cell H2O) are [K]i, 150; [Na]i, 20; and [Cl]i, 50. Ouabain (10(-4) M) causes a rise in [Na]i and a reciprocal loss of intracellular K.
Persistent increase in glucose uptake by rat skeletal muscle following exercise
Authors: Ivy J. L. , Holloszy J. O.
Published: December 2017

The effect of a bout of exercise on glucose uptake and glycogen synthesis in skeletal muscle was examined using a perfused rat hindlimb preparation. Rats were subjected to a bout of swimming. The exercise stress was moderate as reflected in a reduction of muscle glycogen concentration of only 50%. Glucose uptake and glycogen synthesis were measured in perfused hindlimb muscles for a 30-min period beginning approximately 60 min following the exercise. The rate of glucose uptake in the absence of insulin was 10-fold higher in hindlimbs of exercised animals than in the controls. The rate of glucose uptake was also higher in exercised than in control muscles in the presence of 50 microunits/ml or 10 mU/ml of insulin, but these differences were smaller than that found in the absence of insulin. Conversion to glycogen was the major pathway for disposal of the glucose taken up by muscle. The rate of glycogen accumulation in the exercised plantaris muscles was greater than in the control muscles both in the absence and presence of insulin.
Transmembrane potential of rat hepatocytes in primary monolayer culture
Authors: Wondergem R.
Published: December 2017

Transmembrane potentials of rat hepatocytes in primary monolayer culture on collagen gels were measured with glass microelectrodes. Potentials for cells in culture for 23-30 h comprised two populations. The mean +/- SD for a population of stable low potentials was -9.7 +/- 2.0 mV (n = 93). This was compared with -23.6 +/- 9.4 mV (n = 42), the mean value for stable potentials that followed spontaneous increases in the low potentials, 0.5-2.0 min after the impalement. The estimated input resistance increased during these spontaneous hyperpolarizations. In some cells, after 48 h in culture, the transmembrane potential oscillated rhythmically, with an amplitude of 25 mV and a period of 7 min. Suffusing the cells with 120 mM potassium chloride decreased the potential and eliminated the oscillations. The stable high potentials were considered more accurate estimates of the hepatocyte transmembrane potential, based on comparison with values for intact liver. Low potentials may have resulted from current leaking through an electrode shunt resistance, followed by an increase in potential as the membrane "sealed" the shunt pathway. However, these events may also reflect cells capable of two stable transmembrane potentials.
Selective breeding of chickens for erythrocytes with high and low leucine transport activity
Authors: Somes R. G. , Smagula R. M. , Lerner J.
Published: December 2017

Two lines of chickens, one high and the other low uptake, have been selected for three generations for their ability to transport leucine into erythrocytes. Significant line differences were produced in one generation of selection with further separation resulting in later generations. Selection progress has been exclusively with the high-uptake line, the low line not differing significantly from the control. The maximal rate of leucine uptake, the stimulation of leucine transport by medium Na+, lysine uptake, and the Na+-K+-ATPase activity all were greater in the high line. Rates of glucose transport were not different between the lines nor were intracellular concentrations of Na+ or K+.
Metabolism of L-lactate by LLC-PK1 renal epithelia
Authors: Mullin J. M. , Cha C. J. , Kleinzeller A.
Published: December 2017

LLC-PK1 renal epithelial cells do not appreciably synthesize D-glucose or glycogen from L-lactate under the conditions described. [U-14C]L-lactate is metabolized to [14C]L-alanine and [14C]L-glutamate. Synthesis of alanine but not glutamate is decreased by the transaminase inhibitor, aminooxyacetate. LLC-PK1 cells also produce unlabeled urea in the presence of [14C]L-lactate. Evidence for net gluconeogenesis has thus not been obtained for this cell line. This is interesting because the LLC-PK1 cells possess an active sugar transport system, and both active sugar transport and gluconeogenesis are localized together in vivo in the proximal tubule.
Effects of butyrate on ouabain-sensitive respiration of hamster brown adipocytes
Authors: O'Donnell M. E. , Horwitz B. A.
Published: December 2017

Brown adipose tissue is an important site of cold-induced nonshivering thermogenesis in many mammals. The plasma membrane-bound Na+-K+-ATPase has been shown to be significantly involved in this thermogenesis although its exact role is unknown at present. Evidence that coupling of oxidative phosphorylation to electron transport may become loosened during thermogenesis has prompted an investigation of potential roles of the Na+-K+ pump that would be compatible with altered respiratory coupling. One such role is that of modulating norepinephrine (NE)-induced lipolysis and hence provision of free fatty acids to the mitochondria. Under such conditions, inhibition of the pump would reduce NE-induced respiration by limiting substrate availability. If, in fact, the primary role of the pump in NE-induced thermogenesis is to facilitate substrate availability, provision of exogenous substrate should bypass this involvement and ameliorate the ouabain inhibition of respiration. In the present study, this possibility was examined by determining the effect of an exogenous substrate, butyrate, on the contribution of the Na+-K+ pump to NE-stimulated respiration of isolated hamster brown adipocytes. Although exogenous butyrate was able to serve as a substrate for brown adipocyte respiration, its presence had no significant effect on the ouabain sensitivity of NE-induced rates of oxygen consumption. That is, ouabain (1 mM) inhibited the NE-evoked thermogenesis of the adipocytes by 77.7 +/- 6.5% in the absence of butyrate (2 mM) and by 73.4 +/- 9.9% in its presence. It appears, therefore, that the contribution of the Na+-K+ membrane pump to brown fat thermogenesis does not simply reflect modulation of NE-evoked lipolysis.
Erythrocyte permeability to lipophilic solutes changes with temperature
Authors: Garrick R. A. , Patel B. C. , Chinard F. P.
Published: December 2017

Studies of permeability coefficients of biological barriers to members of homologous series can provide information of value in assessing barrier characteristics. To this end, we have determined the linear diffusion coefficients of tracer water (THO), [14C]antipyrine, [14C]acetamide, and n-[14C]alcohols over the range of 10-37 degrees C for dog erythrocytes (D), hemoglobin (D2), and plasma (D1). Permeability coefficients (Po) calculated with the series-parallel pathway model are higher than Po for water at 37 degrees C for all the alcohols except hexanol. Po for acetamide and antipyrine are considerably lower than Po for water at 37 degrees C. The apparent activation energies (Ea) for Po of acetamide and the C1, C2, and C3 alcohols are 10.5 kcal.mol-1, similar to the values obtained with epithelial or lipid bilayers. The Ea's for the larger alcohols are 2-4 kcal.mol-1. The Ea for Po of water is 5.3 kcal.mol-1, similar to the Ea for self-diffusion of water; Ea for antipyrine is 25 kcal.mol-1. We interpret these results to indicate heterogeneity of membrane-solute interactions or of membrane pathways in the erythrocyte for lipid-soluble molecules that is related to both lipid solubility and solute size, as we have suggested in an earlier study and confirmed experimentally in the present one.
Potassium transport by rabbit descending colon
Authors: McCabe R. , Cooke H. J. , Sullivan L. P.
Published: December 2017

Unidirectional mucosal-to-serosal (Jm leads to s) and serosal-to-mucosal (Js leads to m) fluxes of potassium and sodium were determined simultaneously on paired sections of descending colon from the same rabbit under short-circuit conditions. In 13-16 pairs of tissues, net potassium secretion and sodium absorption averaged 0.49 +/- 0.08 and 4.0 +/- 0.8 mueq.cm-2.h-1, respectively. Short-circuit current (Jsc) averaged 3.7 +/- 0.4 mueq.cm-2.h-1 and was approximately equal to the algebraic sum of net potassium and sodium fluxes. Treatment of both sides of the colon with 10(-4) M ouabain reduced the Jsc and transmural potential difference to near zero. Ouabain abolished net potassium secretion by reducing JKs leads to m and abolished net sodium absorption by inhibiting JNam leads to s. In the presence of ouabain, net potassium absorption averaging 0.15 +/- 0.07 mueq.cm-2.h-1 (n = 11) was observed. In the presence of 10(-3) M 2,4-dinitrophenol, both net potassium and net sodium fluxes were abolished, primarily as a result of a reduction in JKs leads to m and JNam leads to s without altering JKm leads to s and JNas leads to m. These results suggest that the rabbit descending colon has the capacity to secrete and possibly to absorb potassium by active mechanisms requiring metabolic energy. Comparison of potassium and sodium fluxes suggest that the paracellular pathway in the rabbit colon is not potassium selective.
Catecholamine sensitivity in brown fat cells from cold-acclimated hamsters and rats
Authors: Nedergaard J.
Published: December 2017

Brown fat cells, freshly isolated from cold-acclimated hamsters and rats, did not respond to norepinephrine addition with the characteristic increase in oxygen consumption (heat production) seen in cells from control animals. However, incubation of these cells for 1 h in a Krebs-Ringer bicarbonate buffer, in the presence of 10 mM pyruvate, fully restored norepinephrine responsiveness. Cells treated in this way from cold-acclimated hamsters (a hibernator) increased the rate of oxygen consumption after maximal norepinephrine stimulation as much as cells from control hamsters; also norepinephrine-stimulated fatty acid release was unaltered, indicating that brown fat cells may partly be responsible for the increase in serum fatty acid level seen during arousal from hibernation. Similarly, preincubated cells from cold-acclimated rats (a nonhibernator) increased oxygen consumption and fatty acid release as much as cells from control rats; this suggests that also in cold-acclimated rats brown fat may supply the circulation with fatty acids during cold stress. Cells from cold-acclimated animals were, however, about 10 times less sensitive to norepinephrine than cells from control animals; this desensitization may be the result of a stimulated phosphodiesterase.