bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of NH4+ and Li+ with the renal microvillus membrane Na+-H+ exchanger
Authors: Kinsella J. L. , Aronson P. S.
Published: December 2017

We have examined the interaction of NH4+ and Li+ with the Na+-H+ exchanger in rabbit renal microvillus membrane vesicles. Alkalinization of the intravesicular space, monitored with [14C]DMO uptake by flow dialysis, resulted from the addition of Cl- salts of Na+, Li+, or NH4+ to the external medium. The 22Na+ uptake rate, assayed by a rapid filtration technique, was saturable with respect to external Na+ concentration (KT 6 mM Na+) and was competitively inhibited by external Li+ (Ki 1.9 mM) and NH4+ (Ki 4.3 mM). Efflux by 22Na+ from vesicles preloaded with Na+ was stimulated by external Na+ and NH4+ but inhibited by external Li+. We conclude that the renal microvillus membrane Na+-H+ exchanger has affinity for Li+ and NH4+ and can mediate the exchange not only of Na+ for H+ but also of Na+ for Na+, Na+ for Nh4+, Li+ for H+, possibly NH4+ for H+, and perhaps Li+ for Na+. The physiological significance of exchange modes other than Na+-H+ exchange is not certain at present, but Na+-NH4+ exchange could play a role in the proximal tubular acidification process.
Role of Ca2+ and myosin light chain phosphorylation in regulation of smooth muscle
Authors: Aksoy M. O. , Murphy R. A. , Kamm K. E.
Published: December 2017

The time course of phosphorylation of the 20,000-dalton myosin light chain (LC 20) was determined during contraction and relaxation in K+- and histamine-stimulated medial strips of swine carotid arteries. Resting LC 20 phosphorylation levels of 0.15 mol P/mol LC 20 rapidly increased to peak values of 0.6-0.7 mol P/mol LC 20 after stimulation and then declined significantly, although stress continued to rise to a stable steady-state maximum. LC 20 dephosphorylation after agonist washout preceded the decline in isometric stress. Over the entire contraction-relaxation cycle, phosphorylation was correlated with shortening velocity and not with developed stress. The maximum shortening velocity with no external load (Vo) was directly proportional to LC 20 phosphorylation (r = 0.986). The data indicate that LC 20 phosphorylation is necessary for cross-bridge cycling leading to shortening or stress development but that stress can be maintained by additional mechanisms. We suggest that dephosphorylation of an attached cross bridge in the presence of Ca2+ arrests the cycle, forming an attached, noncycling cross bridge.
Insulin stimulation of Na+ transport and glucose metabolism in cultured kidney cells
Authors: Fidelman M. L. , May J. M. , Biber T. U. , Watlington C. O.
Published: December 2017

A line of toad kidney cells (A6) in continuous culture was evaluated for ion transport and metabolic responses to insulin. The cells were grown on permeable supports to allow access of the medium to both basolateral and apical sides of the epithelium. Insulin, on the basolateral side only, produced an increase in short-circuit current (Isc) that was maximal at 40-60 min. A concentration-dependent increase in Isc and potential difference (PD) was found in the range of 10-3.2 X 10(3) microunits/ml insulin. The maximal stimulation of Isc and PD was approximately six- and twofold, respectively. After insulin exposure Isc was equivalent to net Na+ transport, indicating active Na+ transport stimulation. Insulin was also found to increase the incorporation of radiolabeled glucose into glycogen. Thus A6 cells exhibit both transepithelial transport and metabolic responses to insulin.
Separation of carotid body chemoreceptor responses to O2 and CO2 by oligomycin and by antimycin A
Authors: Mulligan E. , Lahiri S.
Published: December 2017

The cat carotid chemoreceptor O2 and CO2 responses can be separated by oligomycin and by antimycin A. Both of these agents greatly diminish or abolish the chemoreceptor O2 response but not the nicotine or CO2 responses. After either oligomycin or antimycin, the responses to increases and decreases in arterial CO2 partial pressure (PaCO2) consisted of increases and decreases in activity characterized respectively by exaggerated overshoots and undershoots. These were eliminated by the carbonic anhydrase inhibitor, acetazolamide, suggesting that they resulted from changes in carotid body tissue pH. The steady-state PaCO2 response remaining after oligomycin was no longer dependent on arterial O2 partial pressure (PaO2). All effects of antimycin were readily reversible in about 20 min. The separation of the responses to O2 and CO2 indicates that there may be at least partially separate pathways of chemoreception for these two stimuli. The similarity of the oligomycin and antimycin results supports the metabolic hypothesis of chemoreception.
Chloride self-exchange in toad skeletal muscle in vivo and in vitro
Authors: Macchia D. D.
Published: December 2017

The exchange of cellular Cl with 36Cl has been measured in saline-perfused hindlimb muscles of the pithed toad and compared with cellular Cl exchange in isolated muscles incubated in the vitro either in toad Ringer solution or in toad plasma. In the perfused hindlimb, the rate of 36Cl efflux from muscle cells [17.0 +/- 0.9 pmol Cl.(cm2 plasma membrane.s)-1] was only 40% as fast as that of the 36Cl influx. The discrepancy between Cl influx and efflux was accompanied by a cellular accumulation of Cl against the electrochemical gradient for this anion. Concurrently, the cells took up Na in amounts at least equal to the accumulated Cl. During this accumulation of Na and Cl, the mean resting potential remained constant at a value of -89.2 +/- 1.9 (SE) mV. Na and Cl were taken up by the muscle cells of the perfused hindlimb without a concomitant decrease in cellular K content; i.e., without evidence of inhibition of the Na-K pump. The rate constant for cellular 36Cl efflux from isolated toad muscles preincubated for 3 h in vitro in toad Ringer solution was about five times faster than that of muscles in the perfused hindlimb and similar in magnitude to published values for Cl fluxes in frog muscle. Cellular Cl efflux from muscles briefly preincubated in vitro for 15 min instead of 3 h was significantly slower than after prolonged preincubation. In vitro incubation of isolated toad muscles in toad plasma slowed the cellular 36Cl efflux to values approaching those measured in the perfused hindlimb, without comparably depressing the 36Cl influx. It is suggested that the uptake of NaCl by the cells of perfused hindlimb muscle may proceed by an electroneutral inward cotransport of Na and Cl on the same carrier.
Regression of skeletal muscle of chicken wing after stretch-induced hypertrophy
Authors: Sparrow M. P.
Published: December 2017

Regression of stretch-induced growth of the anterior latissimus dorsi muscle of the adult fowl was characterized by measuring weight, protein, RNA, DNA, and collagen content. After 7 days of hypertrophy the total amount of protein, RNA, DNA, and collagen increased by 59, 228, 82, and 23%, respectively, above the control contralateral muscle. On removal of the stimulus, regression back to normal weight and composition was complete in 13 days except for total DNA content, which was still elevated 21% after 29 days of regression. After 28 days of hypertrophy, the total amount of protein, RNA, DNA, and collagen were 100, 126, 96, and 27%, respectively, greater than controls. On removal of the stimulus regression was again rapid, but reversal of the hypertrophy was not complete 35 days later with the total protein and RNA still elevated by 16–22% and the total DNA 35% above control level. The increase in the total collagen during hypertrophy was attributable to about equal increases in both the epimysial collagen and the internal collagen of the muscle. The study shows that reversal of hypertrophy can occur almost as rapidly as the hypertrophy process. RNA and protein are lost more rapidly than DNA.
The role of estrogen receptor in Xenopus laevis vitellogenin gene expression
Authors: Hayward M. A. , Brock M. L. , Shapiro D. J.
Published: December 2017

Administration of estradiol 17 beta [estra-1,3,5(10)-triene-3,17-beta-diol] to male Xenopus laevis induces the massive synthesis by the liver of the egg yolk precursor phospholipoglycoprotein, vitellogenin, and its cognate mRNAs. Restimulation of male X. laevis that have been previously induced to synthesize vitellogenin mRNA but are inactive in vitellogenin mRNA synthesis at the time of restimulation with estrogen results in more rapid accumulation of vitellogenin mRNA and more efficient transcription of the vitellogenin genes than occurs following primary estrogen stimulation. The estrogen receptor system that mediates estrogen action in this organism exhibits several unusual properties. The cytoplasm of unstimulated liver cells contains high levels of a middle-affinity estrogen-specific binding protein and little if any estrogen receptor. The properties of the estrogen binding protein are consistent with a role in protecting estradiol 17 beta against metabolism, as a fraction of cytoplasmic estradiol 17 beta is not subject to rapid metabolism. In addition, similar binding activities are found in all Xenopus tissues surveyed that respond to steroid hormones. The induction of nuclear estrogen receptor is coincident with the onset of vitellogenin mRNA accumulation. However, an increased level of estrogen receptor is not responsible for the elevated rate of vitellogenin gene transcription observed following restimulation with estrogen.
31P nuclear magnetic resonance analysis of frog skin
Authors: Lin L. E. , Shporer M. , Civan M. M.
Published: December 2017

The intracellular phosphate composition of whole and split frog skins has been studied by 31P nuclear magnetic resonance (NMR) analysis. The spectra were similar to those previously recorded from isolated epithelial cells of toad bladder. However, qualitative differences were noted in comparison with spectra from whole toad bladder. The 31P spectra from whole frog skin reflect the intracellular compositions of the epithelial cells, whereas subepithelial elements contribute significantly to the total observed 31P signals from toad bladder. Analyzed at 4 degrees C, the average phosphocreatine (PCr) and ATP concentrations of frog skin are of similar magnitude. The ratio of [PCr] to [ATP + ADP] depends on time, tissue oxygen tension, temperature, and extracellular inorganic phosphate concentration. Both this ratio and the short-circuit current (measured in parallel experiments) fell during the course of aerating frog skins in Ringer solution at room temperature. The intracellular inorganic phosphate (Pi) signal was identified. After reduction of extracellular pH, the signal did not shift immediately but subsequently did undergo an acid shift.
Increase in K+ and alpha-AIB active transport in CHO cells after low [K+] treatment
Authors: Graves J. S. , Wheeler D. D.
Published: December 2017

We have studied the effects of prolonged incubation in low [K+] medium (approximately 0.3 mM) on both K+ and amino acid transport in Chinese hamster ovary (CHO) cells. When incubated in low [K+] medium, CHO cells redressed partially the loss of intracellular K+ after 12 h. After 24 h of incubation, both the activity of Na+-K+-ATPase in crude homogenates, and the transport capacity (Vmax) for ouabain-sensitive (i.e., active) K+ influx approximately doubled. The magnitude of the ouabain-insensitive (i.e., passive) K+ influx decreased by 50%. Thus the regulatory response involves an apparent increase in Na+-K+ pump and a decrease in K+ leak. The transport capacity for the nonmetabolized amino acid, alpha-aminoisobutyric acid (alpha-AIB), also increased after 24 h in low [K+] medium. The Vmax for the Na+-dependent (i.e., active) alpha-AIB influx increased by about 150%, and the magnitude of the Na+-independent influx increased by 20-40%. These changes in alpha-AIB transport result in a twofold greater capacity to accumulate this amino acid. Thus the regulation of K+ and alpha-AIB transport systems appears to be linked and possible mechanisms of this linkage are discussed.
Coupled NaCl entry into Necturus gallbladder epithelial cells
Authors: Ericson A. C. , Spring K. R.
Published: December 2017

NaCl entry into Necturus maculosus gallbladder epithelial cells was studied by determination of the rate of fluid movement into the cell when the Na+-K+-ATPase was inhibited by 10(-4) M ouabain in the serosal bathing solution. The cell swelling was due to continuing entrance of NaCl into the cell across the apical membrane, which increased the solute content of the cell; the resultant rise in cell osmolality induced water flow and cell swelling. The rate of swelling was 4.3% of the cell volume per minute, equivalent to a volume flow across the apical membrane of 1.44 x 10(-6) cm/s, similar in magnitude to the normal rate of fluid absorption by the gallbladder. We determined the mechanism of NaCl entry by varying the ionic composition of the mucosal bath; when most of the mucosal Na+ or Cl- was replaced, cell volume did not increase during pump inhibition. The rate of NaCl entry was a saturable function of Na+ or Cl- in the mucosal bathing solution with K1/2 values of 26.6 mM for Na+ and 19.5 mM for Cl-. The mode of NaCl entry was probably not the parallel operation of Na+-H+ and Cl(-)-HCO-3 exchangers because of the lack of effect of bicarbonate removal or of the inhibitors amiloride and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid. NaCl entry was reversibly inhibited by bumetanide in the mucosal bathing solution. Transepithelial NaCl and water absorption is the result of the coupled, carrier-mediated movement of NaCl into the cell across the apical membrane and the active extrusion of Na+ by the Na+-K+-ATPase in the basolateral membrane.
Volume regulation by Necturus gallbladder: apical Na+-H+ and Cl(-)-HCO-3 exchange
Authors: Ericson A. C. , Spring K. R.
Published: December 2017

Necturus gallbladder epithelial cells exhibited volume regulatory swelling when exposed to a hypertonic mucosal bathing solution. The initial, osmotically induced shrinkage was followed by a rapid increase in cell volume back to the control value despite continuing hypertonicity of the mucosal perfusate. This volume regulatory increase occurred by osmotic water flow accompanying the transient cellular uptake of NaCl from the mucosal bathing solution. Volume regulatory increase required Na+ and Cl- in the mucosal bath; it was inhibited by amiloride or 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid but not by bumetanide or ouabain. The K1/2 for Na+ was 2.8 mM, the K1/2 for Cl- was 1.9 mM, and maximum velocity of fluid flow into the cell for both ions was greater than 10 x 10(-6) cm/s. Both volume regulatory increase and transepithelial fluid absorption involve NaCl flux across the apical membrane into the cells, but the nature of the NaCl fluxes differ in the two processes. During volume regulatory increase NaCl enters the cells by parallel Na+-H+ and Cl(-)-HCO-3 exchanges, whereas during transepithelial fluid absorption NaCl enters the cell by the coupled flux of NaCl.
Stimulation of Na+-Ca2+ exchange in cardiac sarcolemmal vesicles by proteinase pretreatment
Authors: Philipson K. D. , Nishimoto A. Y.
Published: December 2017

The Na+-Ca2+ exchange activity of purified canine cardiac sarcolemmal vesicles can be strikingly stimulated if the vesicles are pretreated with a serine or thiol proteinase. The Km (Ca2+) for Na+i-dependent Ca2+ influx is reduced from 22.2 +/- 2.3 to 8.1 +/- 0.3 microM while Vmax is increased from 15.1 +/- 3.6 to 18.9 +/- 5.2 nmol Ca2+ . mg protein-1 . s-1. Na+o-dependent Ca2+ efflux is also stimulated by proteinase pretreatment although passive (Na+-independent) Ca2+ efflux from the sarcolemmal vesicles is unaffected. Proteinase treatment reduces the sensitivity of Na+-Ca2+ exchange to the inhibitors chlorpromazine and polymyxin B, but not to the inhibitor, palmitylcarnitine. Using a newly developed technique we are able to demonstrate that the Na+-Ca2+ exchange of inside-out sarcolemmal vesicles is being stimulated by proteinase treatment (Philipson, K. D., and A. Y. Nishimoto, J. Biol. Chem: 257, 5111-5117, 1982; this technique uses the ATP-dependent Na+ pump to preload only inside-out vesicles with Na+ prior to Na+-Ca2+ exchange). Right-side-out vesicles may also be stimulated.
Membrane permeability of isolated lung cells to nonelectrolytes at different temperatures
Authors: Garrick R. A. , Chinard F. P.
Published: December 2017

Membrane permeability coefficients (P0) of rabbit lung cells consisting primarily of alveolar epithelial and endothelial cells and of alveolar macrophages from dog lungs were determined for tritiated water, n-[14C]alcohols, and [14C]antipyrine over the temperature range 10 to 37 degrees C with the series-parallel pathway model. In the mixed cell preparation both the diffusional permeability to water (755 X 10(-5) cm.s-1 at 37 degrees C) and the response to temperature change (apparent activation energy, Ea, 10 kcal.mol-1) are greater than the corresponding values in the macrophages (110 X 10(-5) cm.s-1 and 4.8 kcal.mol-1, respectively). The permeability coefficients for the small alcohols (C1-C3) are similar and considerably higher than for water in both cellular preparations. The values of the permeability coefficients and the temperature dependence for antipyrine and the larger alcohols in the mixed lung cells differ from the values obtained in the macrophages. Comparison of our results with those obtained in erythrocytes and Novikoff hepatoma cells demonstrates the differences in water permeability in each cell preparation and the similarity in permeation for the more lipophilic solutes in the cell preparations. These differences may be important in the comparison of results obtained in isolated cellular systems and in intact tissues and organs.
Effects of changes in serosal chloride on electrical properties of toad urinary bladder
Authors: Narvarte J. , Finn A. L.
Published: December 2017

Conventional microelectrode and tracer flux techniques were used to study the effects of reduction in serosal chloride concentration ([Cl]s) on the electrical properties of toad urinary bladder epithelium. Reduction in [Cl]s resulted in a transient change in transepithelial potential (Vms) (and of apical and basolateral membrane potentials) that was inversely dependent on the base-line values of those potentials. In all cases, however, there was a decrease in transepithelial resistance (Rt) that was explained by an increase in the sodium conductance of the apical membrane. In tissues in which the transepithelial potential increased, there was a rise in the active mucosal-to-serosal sodium flux. The increase in conductance was directly related to the increase in short-circuit current. The changes in Vms and Rt brought about by reduction in [Cl]s were prevented by agents known to modify sodium transport, including low mucosal sodium concentration, addition of amiloride or amphotericin B to the mucosal solution, or of ouabain to the serosal solution. The results are best explained by a primary effect of chloride reduction on sodium extrusion across the basolateral membrane, with a secondary increase in apical sodium conductance. In addition, the data provide new evidence for the existence of a basolateral chloride conductance pathway.
K562 cell anion exchange differs markedly from that of mature red blood cells
Authors: Law F. Y. , Steinfeld R. , Knauf P. A.
Published: December 2017

Human K562 leukemic cells exhibit several erythroid properties, including synthesis and expression of the major red blood cell sialoglycoprotein, glycophorin. This has led us to ask if these cells express a functional anion transport system analogous to that which is associated with the other major erythrocyte glycoprotein, band 3. The chloride-36 exchange flux in K562 cells is less than 0.6% of that which would be expected in mature erythrocytes under similar conditions. Unlike red blood cells, K562 cells do not exhibit a high chloride-sulfate selectivity, and various agents that inhibit red blood cell chloride exchange are all much less effective in K562 cells. On the basis of these flux measurements, K562 cells probably contain less than 600 fully functional red blood cell-like band 3 molecules per cell, in contrast to about a million molecules in the mature red blood cell. The possible-existence of greatly altered band 3 molecules with a reduced turnover rate and/or a reduced affinity for chloride and for various inhibitors is unlikely but cannot be completely excluded. Anion transport was also measured in K562 cells that had been induced to increase hemoglobin synthesis by various chemical agents. Even under these conditions, chloride fluxes indicated no substantial increase in the number of functional anion transport sites or their chloride transport rate.
Avian shell gland contractility: interaction of PGF2 alpha and arginine vasotocin with Ca2+
Authors: Olson D. M. , Hertelendy F.
Published: December 2017

The effects of prostaglandin F2 alpha (PGF2 alpha) and arginine vasotocin (AVT) on the isometric contractile activity of avian shell gland longitudinal muscle strips were studied in relation to the role of extracellular Ca2+. PGF2 alpha and AVT stimulated contractile tension in a dose-related manner. This was attenuated when either of the Ca2+ channel blockers verapamil or R33956 was added to the muscle chamber baths. Ca2+-free solution containing 1 mM ethyleneglycol-bis (beta-aminoethylether)-N,N'-tetraacetic acid completely prevented contraction in response to increasing doses of PGF2 alpha or AVT. Washing of the strips with Ca2+-free solution eliminated spontaneous contractile activity, but replenishment of CaCl2 to the medium (0.1-5.0 mM) restored it. Addition of PGF2 alpha to the Ca2+-free medium enhanced contractile tension during Ca2+ replenishment, whereas AVT had no effect on tension generation at low extracellular Ca2+ concentration (0.1-0.5 mM) but increased it at higher extracellular Ca2+ concentration (1.0-5.0 mM). PGF2 alpha stimulation was sensitive to extracellular Na+ concentration, whereas AVT-induced activity was not. Potassium depolarization (20 mM K) potentiated PGF2 alpha-stimulated activity, whereas the response to AVT was unaffected. At 127.5 mM K, AVT-stimulated activity was inhibited. PGF2 alpha-enhanced Ca2+-dependent tension generation was right shifted in a dose-related manner by AVT. These results suggest that extracellular Ca2+ is necessary for the full expression of PGF2 alpha- and AVT-stimulated muscle contraction and suggest that each agonist has a different mechanism of action.
Facilitated calcium diffusion by intestinal calcium-binding protein
Authors: Feher J. J.
Published: December 2017

The calcium flux through an aqueous compartment was determined using a flow-through dialysis cell in which two dialysis membranes isolated the aqueous compartment. Addition of the intestinal vitamin D-dependent calcium-binding protein (CaBP) significantly enhanced the calcium flux at near physiological calcium concentrations (1 X 10(-6) M). Bovine serum albumin had no effect on the calcium flux. CaBP appears to be one of a class of low molecular weight, soluble binding proteins that enhance ligand diffusion.
LHRH self priming of gonadotrophin secretion: time course of development
Authors: Waring D. W. , Turgeon J. L.
Published: December 2017

The luteinizing hormone-releasing hormone (LHRH) self-priming effect, in which the gonadotrophin secretory response to LHRH is augmented by prior exposure to LHRH, was studied in vitro using pituitaries of proestrous rats. Individual, quartered anterior pituitaries were superfused for 6 h at 1 ml/min. Using two or three 10-min LHRH pulses of 0.8 nM in which the interpulse interval was 20-170 min or a single 2-h LHRH pulse of 0.8 nM, LHRH self priming of luteinizing hormone (LH) secretion was demonstrable within 30-40 min of LHRH exposure. LHRH self priming of follicle-stimulating hormone occurred 40-50 min after the start of LHRH exposure. The first derivative of the 2-h LHRH pulse rate of secretion vs. time curve provided a sensitive indicator of the time required for development of the self-priming response. Once initiated by a 10-min LHRH pulse, priming of LH secretion persisted with no decrease, as determined by the area under the secretion rate vs. time curve and by the slope of the rise of this curve, over the longest interpulse interval examined, 170 min. The observed time course of development and persistence of LHRH self priming are consistent with its presumed important role in development of the preovulatory gonadotrophin surges.
Kidney epithelial cell growth is stimulated by lowering extracellular potassium concentration
Authors: Walsh-Reitz M. M. , Toback F. G.
Published: December 2017

The factors that induce kidney growth in K+-depleted animals are unknown. To determine if the low extracellular fluid K+ concentration could act as a growth stimulus, cultures of monkey kidney epithelial cells from the BSC-1 line were studied in media with a low-K+ concentration. Growth of confluent cultures was accelerated maximally at a K+ concentration of 3.2 mM, whereas concentrations of 2.9 and 3.5 mM were also stimulatory but to a lesser extent. Because growing renal tissue from K+-depleted rats was previously found to exhibit increased uptake of nutrient molecules, evidence for enhanced uptake was sought in BSC-1 cells after exposure to low-K+ medium. The uptake of 10 different nutrient molecules was enhanced in cells exposed to low-K+ medium for 30 s. These observations indicate that a reduced extracellular K+ concentration per se stimulates proliferation of renal epithelial cells in culture and could be one of the factors that mediate kidney growth in K+-depleted animals.
Uptake of latex particles by macrophages: characterization using flow cytometry
Authors: Parod R. J. , Brain J. D.
Published: December 2017

Flow cytometry can be used to characterize the uptake of particles by small samples of pulmonary macrophages both quickly and accurately. We found that there was a linear relationship between the number of fluorescent latex particles and the fluorescent intensity associated with each cell up to 47 particles/cell. Macrophages lavaged from the lungs of Syrian golden hamsters were metabolically and functionally stable for 3 h of incubation; the average intracellular concentrations of Na+ and K+ were 29 +/- 2 and 158 +/- 6 mM, respectively. Particle uptake was significantly inhibited by removing divalent cations with ethylenediaminetetraacetic acid and lowering the incubation temperature (37 degrees C) to 24 and 3 degrees C. The cell-to-cell variability in the uptake of particles was greater than the Poisson distribution would predict based on the mean number of particles per cell.
Effects of insulin and tunicamycin on neuronal insulin receptors in culture
Authors: Boyd F. T. , Raizada M. K.
Published: December 2017

We have examined the effect of insulin and tunicamycin, which cause decreases in cell surface insulin receptor numbers in peripheral tissues, on insulin receptors in neuron-enriched brain cell cultures. Incubation with 0.016-0.83 microM insulin for 24 h failed to decrease the specific binding of 125I-insulin in neuron-enriched cultures prepared from whole brains of 1-day-old rats. In contrast, these concentrations of insulin produced a dose-dependent decrease in the binding of 125I-insulin in fibroblastic cultures. Tunicamycin, an antibiotic which inhibits glycosylation of proteins and greatly reduced insulin binding via a reduction in apparent receptor numbers in fibroblastic cultures, caused no decrease in the binding of 125I-insulin in neuron-enriched cultures. These results indicate that brain insulin receptors are not down regulated by insulin and that glycosylation of insulin receptors may not be an important step in the regulation of their surface expression in the brain.
Vasopressin stimulates growth of renal epithelial cells in culture
Authors: Walsh-Reitz M. M. , Toback F. G.
Published: December 2017

The hypothesis that arginine vasopressin could regulate kidney epithelial growth by its effect on Na+ transport was examined in cultures of cells from the BSC-1 line. Addition of vasopressin (75 pg/ml) or NaCl (25 mM) to the medium stimulated growth of confluent cultures but retarded growth of sparse cells in the presence of 0.5% calf serum. Thus the capacity of vasopressin or exogenous NaCl to regulate growth of BSC-1 cells was cell density dependent. Vasopressin stimulated growth of confluent cultures only in the narrow concentration range of 50-100 pg/ml (approximately 10(-10)M), whereas concentrations of 10 pg/ml and 125-1,000 pg/ml had no effect. In contrast, vasopressin at or above concentrations of 10 pg/ml raised cell Na+ content to its maximal value, which indicated that the hormone could increase the Na+ content of cells without necessarily stimulating their growth. To determine if vasopressin modulates growth by acting on the plasma membrane, nutrient transport and ligand binding were assessed in high-density quiescent cultures. The hormone augmented uptake of alpha-aminoisobutyric acid and binding of epidermal growth factor, whereas the addition of NaCl (25 mM) did not. Thus growth stimulation by vasopressin was associated with increased cell Na+ content, enhanced uptake of an amino acid, and augmented binding of a growth factor. These observations suggest that the growth-promoting effect of vasopressin is not a simple function of its capacity to alter cell Na+ flux but could be mediated by other actions of the hormone, perhaps at the level of the plasma membrane.
Effects of "loop" diuretics on ion transport by dog tracheal epithelium
Authors: Widdicombe J. H. , Nathanson I. T. , Highland E.
Published: December 2017

The "loop" diuretics MK-196, bumetanide, piretanide, and furosemide are all potent inhibitors of Cl transport by the dog's tracheal epithelium. In short-circuited tissues, the drugs caused significant decreases in both unidirectional Cl fluxes and in the net flux of Cl toward the lumen; the change in net Cl flux was not significantly different from the change in short-circuit current. The drugs had no effect on active Na absorption. All drugs caused a significant fall in tissue conductance. All drugs, except MK-196, were more potent from the serosal bath; MK-196 was equipotent from either side of the tissue. In experiments with isolated cells, the diuretics caused no significant changes in intracellular Na and K concentrations, a fall in intracellular Cl concentration, and approximately equal falls in Na and Cl influxes. These results suggest that the site of action of these drugs is on a basolateral linked Na-Cl entry process. Additional evidence for such a linked entry process was provided by experiments in which removal of Cl reduced Na influx and removal of Na reduced Cl influx.
Inhibition of net calcium efflux from bone by ethanol in vitro
Authors: Ramp W. K. , Demaree D. N.
Published: December 2017

Ethanol administered to animals is known to cause hypocalcemia. This investigation was undertaken to evaluate direct early effects of ethanol on the net fluxes of Ca2+ and inorganic phosphate (Pi) into or out of bone using tibiae from 13-day-old chick embryos and 8-day-old suckling rats in vitro. When chick bones were incubated with ethanol in the medium (10 microliters/ml), net Ca2+ efflux was decreased 19, 22, 27, and 31% at 2, 4, 6, and 8 h, respectively. Metabolically inhibited bones showed a net influx rather than efflux of Ca2+ and were not further affected by ethanol. The ethanol had no consistent effect on net Pi efflux and slightly reduced lactate production. At three doses of ethanol (3, 10, and 30 microliters/ml of medium) the reduction of Ca2+ efflux was dose related in both chick and rat bones. Ethanol completely inhibited parathyroid hormone-stimulated, net Ca2+ efflux from chick bones, even at ethanol levels that by themselves did not affect Ca2+ efflux. These findings are consistent with the hypothesis that the hypocalcemia in ethanol-treated animals may be due in part to inhibition of net Ca2+ efflux from bone.
The functional significance of neurotransmitter diversity
Authors: Bloom F. E.
Published: December 2017

A major continuing theoretical issue in neurobiology is the nature of the information encoded into chemical neurotransmitters. This problem has been intensified by major recent advances in cellular neurobiology in three specific areas of work: neuronal connectivity, synaptic mechanisms, and neuronal transmitters. Countless new interneuronal connections have been revealed through the use of sensitive new cellular tracing methods, revealing a far more detailed picture of the complexities and principles of brain organization. A whole range of ionic conductance mechanisms has been detailed by the application of new methods of electrophysiological analysis, particularly useful with the in vitro preparations. Many of these mechanisms were not previously recognized, and together they provide a much richer repertoire of receptor response mechanisms upon which neurotransmitters can operate. Last, the modern methods of chemical analysis have provided an ever-increasing list of new neurotransmitter molecules, which fall conveniently into three chemical categories: amino acids, monoamines, and neuropeptides. This review considers some possible underlying principles by which the rich signaling capacity of the central nervous system may be approached conceptually and experimentally.
Transmembrane 45Ca fluxes in isolated smooth muscle cells: basal Ca2+ fluxes
Authors: Scheid C. R. , Fay F. S.
Published: December 2017

Methods are described for monitoring unidirectional fluxes of 45Ca in smooth muscle cells in suspension. Compartmental analysis of 45Ca influx data indicate that 45Ca exchange consists of two kinetically distinguishable components in the toad stomach muscle cells: a relatively small (approximately 100-pmol X cm-2) component with a rapid rate of exchange (t1/2 approximately 1.4 min) and a larger (approximately 930-pmol X cm-2) component, which exchanges more slowly (t1/2 congruent to 87 min). The rate of exchange of the latter but not the former Ca2+ pool is increased on exposure of the cells to elevated K+ levels; thus the “slow” component of uptake appears to reflect transmembrane Ca2+ flux, whereas the “rapid” component may reflect exchange of surface-bound label. Consistent with this interpretation is the finding that under conditions in which surface 45Ca is rapidly and completely displaced, 45Ca efflux occurs as a simple monoexponential process with a slow rate of exchange (k = 7.80 X 10(-5) s-1). The apparent rate of transmembrane Ca2+ flux in smooth muscle cells at rest is approximately 0.1 pmol X cm-2 X s-1. Cellular processes that could give rise to an apparent transmembrane flux rate of this magnitude are discussed, and a model is presented which appears to describe cellular 45Ca exchange in the isolated smooth muscle cells.
Energetics of isometric contraction in porcine carotid artery
Authors: Krisanda J. M. , Paul R. J.
Published: December 2017

The rate of ATP utilization ( JATP ) and unloaded shortening velocity ( Vus ) of porcine carotid artery were studied during tension development and maintenance to assess the importance of mechanisms proposed to account for its high economy of tension maintenance. Previous work from our laboratory established that the rate of O2 consumption ( JO2 ) can be used to measure rates of tissue phosphagen utilization as early as 30 s after initiation of contraction. Studies at 37 degrees C of tissue JO2 indicated the following. 1) The basal JO2 was 0.069 +/- 0.017 mumol O2 X min-1 X g-1) (n = 10). During steady-state tension maintenance suprabasal JO2 was 0.079 +/- 0.012 mumol O2 X min-1 X g-1 for tissues stimulated with KCl (n = 11) and 0.213 +/- 0.022 (n = 3) for tissues stimulated with KCl + histamine. 2) For both stimulation conditions an initial elevated (peak) suprabasal JO2 was observed that correlated with the rate of tension development. The peak suprabasal JO2 was approximately twice the steady-state suprabasal JO2 measured 10 min after stimulation. 3) There was no significant change in JO2 during tension redevelopment after a rapid length step at 15–20 min after stimulation (n = 4). Studies of Vus indicated the following. 1) During steady-state tension maintenance Vus was 0.008 +/- 0.001 tissue lengths/s for tissues stimulated with KCl (n = 13) tissue lengths/s for tissues stimulated with KCl + histamine (n = 6). 2) An initial twofold peak in Vus was observed at 0.25–0.5 min in that decreased to steady-state levels by 4 min after KCl stimulation, whereas minor decreases in Vus still occurred until 10–20 min after KCl + histamine stimulation. 3) The measured transient in Vus , although biphasic, does not temporally correlate with the transient in JO2 even after the JO2 time course was corrected for delays resulting from O2 diffusion and the electrode response time. The mechanism underlying the observed maximum change of two- to fourfold in both JATP and Vus is not sufficient to account for the high economy of tension maintenance.
Stimulation of DNA synthesis in kidney epithelial cells in culture by potassium
Authors: Toback F. G. , Ekelman K. B. , Ordonez N. G.
Published: December 2017

The hypothesis that the K+ concentration of extracellular fluid is a determinant of renal DNA synthesis was examined in quiescent, high-density cultures of monkey kidney epithelial cells of the BSC-1 line. The addition of KCl to the medium increased the number of cells engaged in DNA synthesis in a concentration-dependent manner. The capacity of K+ to stimulate DNA synthesis in a greater number of cells was additive with exogenous NaCl and calf serum and was associated with an increment in the steady-state cell K+ content. Studies with other monovalent cations indicated that the stimulatory effect of K+ on DNA synthesis was not mediated by increments in the chloride concentration or osmotic pressure of the medium. The addition of K+ to confluent cultures was associated with a concentration-dependent increase in cellmultiplication. The commitment of cells to increased multiplication required exposure of the culture to added KCl for longer than 3 but not more than 6 h. Addition of KCl to cultures of mouse fibroblasts did not alter DNA synthesis, multiplication, or cell K+ content. These observations indicate that increased availability of K+ in the extracellular fluid can stimulate DNA synthesis in kidney epithelial cells in culture.
Sodium-sugar coupling stoichiometry in chick intestinal cells
Authors: Kimmich G. A. , Randles J.
Published: December 2017

Sodium-dependent sugar transport systems involve the function of membrane components that couple the transmembrane flow of Na+ to the concomitant flow of certain sugar molecules. The coupling stoichiometry between Na+ and sugar fluxes via these systems must be measured under conditions in which the membrane potential does not change due to the induction of transport or during the interval of flux measurement. This can be accomplished by utilizing gradients of highly permeant ions (NO-3 and K+ plus valinomycin) to create diffusion potentials of sufficient magnitude that the sugar-induced Na+ flux does not introduce an appreciable change in the imposed potential. Under these conditions, the coupling stoichiometry for chicken intestinal cells proves to be 2 Na+:1 sugar as reported earlier for studies performed in the absence of a membrane potential. When control of the potential is not maintained, a coupling ratio of 1:1 is observed. The stoichiometry does not change as a function of Na+ concentration, which suggests that carrier forms with only one Na+ bound do not contribute to the carrier-mediated Na+ or sugar fluxes. When no potential is present, the stoichiometry is modified by the level of intracellular Na+ and sugar in a manner indicative of a transport mechanism in which Na+ must dissociate from the “loaded” carrier at the inward facing membrane surface before the sugar molecule dissociates.
Vasopressin rapidly stimulates Ca2+ efflux from intracellular pool in quiescent Swiss 3T3 cells
Authors: Lopez-Rivas A. , Rozengurt E.
Published: December 2017

Addition of the neurohypophysial nonapeptide [Arg8]vasopressin to 45Ca2+-loaded quiescent cultures of Swiss 3T3 cells or diploid mouse embryo fibroblasts causes a rapid increase (within seconds) in the rate of 45Ca2+ efflux from the cells. This reflects the release of 45Ca2+ from an intracellular store that is partly or entirely derived from mitochondria and leads to a marked decrease (52%) in the intracellular 45Ca2+ content of the cultures under equilibrium 45Ca2+ conditions. The effect is dose dependent, specific, and blocked by a vasopressor antagonist. Prolonged pretreatment with vasopressin that renders the cells unresponsive to the mitogenic effects of the hormone also blocks the Ca2+ response. The results suggest that Ca2+ fluxes may be involved in the mechanism of mitogenic action of vasopressin in Swiss 3T3 cells.
Oncogenes, ions, and phospholipids
Authors: Macara I. G.
Published: December 2017

Recent discoveries in tumor virology, lipid biochemistry, and ion transport studies promise to revolutionize our understanding of cell proliferation, differentiation, and tumorigenesis. A model is proposed, based on similar schemes presented recently by others, that incorporates these discoveries and provides a focus for future research on the functions of oncogene proteins. The model suggests that the early (competence) events in the initiation of cell proliferation are triggered by activation of phosphatidylinositol (PI) turnover, which releases two second messengers, 1,2-diacylglycerol (1,2-DG) and inositol-1,4,5-trisphosphate (IP3). PI turnover is proposed to be regulated by the oncogene protein kinases (src, ros, abl, fps) either directly (acting as PI kinases) or indirectly (as tyrosine kinases). The IP3 triggers Ca2+ release from internal stores, and the elevation of cytosolic Ca2+ acts synergistically with 1,2-DG to activate the Ca2+- and phospholipid-dependent kinase C. Kinase C copurifies with the receptor for the tumor-promoting phorbol esters. It is suggested that kinase C then activates the Na+-H+ exchange system, resulting in an elevation of cytosolic pH and Na+, and that these ionic signals (including the change in Ca2+), either in concert or individually, induce further events, including expression of the protooncogene c-myc, which together commit the cell to initiate replication. Evidences in support of this model are reviewed, together with complications indicating its present inadequacies, particularly recent data suggesting that 1,2-DG may activate tyrosine kinases independent of kinase C.
Influence of aerobic metabolism on IMP accumulation in fast-twitch muscle
Authors: Dudley G. A. , Terjung R. L.
Published: December 2017

Significant activation of AMP deaminase in fast-twitch muscle leads to a loss of ATP and accumulation of NH4 and IMP. Although this occurs during severe metabolic stress caused by intense contraction conditions, the process is probably influenced by the muscle's capacity for aerobic metabolism. We evaluated this possibility during moderately intense (5 Hz) contraction conditions in situ by following the time course of NH4 and IMP accumulation in fast-twitch, low-oxidative white (FTW) and fast-twitch, high-oxidative red (FTR) muscle of the rat. A high rate of IMP formation, resulting in a 50% loss of ATP content, occurred in normal FTW, but not FTR muscle, during contractions when blood flow was intact. Eliminating blood flow prior to contractions, however, removed the distinction between the FTR and FTW muscle. The FTR fiber section now produced a high IMP content and a stoichiometric loss of ATP. Thus the ability of the FTR fiber to sustain this contraction effort without an ATP loss is due to its greater functional capacity for aerobic metabolism. The FTW muscle section of trained animals exhibited a reduced accumulation of IMP and a smaller loss of ATP during the same 5-Hz stimulation. The mitochondrial content and peak blood flow of this FTW fiber section is increased by training. Thus it is probable that the cellular conditions leading to a significant accumulation of IMP in fast-twitch muscle are determined by the metabolic stress established by the contraction effort, relative to the muscle fiber's functional capacity for aerobic metabolism.
Comparison of isolated cells from liver, colon, and kidney of guinea pig
Authors: Burger H. J. , Hauber G. , Schlote W. , Schwenk M.
Published: December 2017

Liver cells, colon epithelial cells, and kidney tubule fragments were isolated from guinea pig using methods previously employed in the rat. All three cell preparations exhibited well-preserved structure. Respiration was highest in kidney tubule fragments (25 nmol O2/mg protein X min) and was well coupled in all preparations. When cells were incubated at 37 degrees C, they accumulated K+ in a ouabain-sensitive manner. Incorporation of [3H]phenylalanine and [3H]uridine into acid-precipitable material proceeded linearly over at least 40 min. The cytochrome P-450 content (175 pmol/mg cell protein) and activity (aminopyrine demethylation) of liver cells exceeded that of the other two preparations 15- to 20-fold. The results indicate good maintenance of function in all three preparations. Because guinea pig epithelial cells exhibit some advantages over isolated cells from other species, the present preparations are well suited for comparing the cell physiology of the respective organs.
Faster protein and ribosome synthesis in thyroxine-induced hypertrophy of rat heart
Authors: Siehl D. , Chua B. H. , Lautensack-Belser N. , Morgan H. E.
Published: December 2017

Rates of protein synthesis and degradation were measured in hearts from normal and thyroxine-injected rats that were perfused as working preparations with Krebs-Henseleit bicarbonate buffer containing 400 microU insulin/ml, 2 mM lactate, 10 mM glucose, and normal plasma concentrations of amino acids. Hearts were perfused after four daily injections (1 microgram/g body wt) of thyroxine. Protein synthesis was 24% greater in hypertrophying hearts compared with controls; ribosomal RNA content increased 25%. In addition, the proportion of total RNA in free ribosomal subunits in hypertrophying hearts was unchanged from perfused hearts of control rats and from unperfused normal hearts. These results indicated that increased protein synthetic machinery as monitored by content of ribosomes, rather than more efficient initiation or elongation of peptide chains, accounted for the faster rate of protein synthesis in hypertrophying hearts. Rates of protein degradation were the same in hearts from thyroxine-injected and control animals. When rates of ribosome production were measured in vitro at various times after a single injection of thyroxine in vivo, faster ribosome synthesis was detected within 8 h; no change in the rate of total protein synthesis occurred after a single injection of thyroxine. These studies indicated that accelerated ribosome formation was an early and quantitatively important factor in cardiac hypertrophy.