Voltage oscillations and ionic conductances in hair cells isolated from the alligator cochlea

Tall hair cells were isolated by enzymatic and mechanical dissociation from selected regions of the apical half of the alligator (A. mississippiensis) cochlea. Single cells were subjected to voltage-clamp and current-clamp using the tight-seal whole-cell recording technique. Most hair cells isolated from the apex of the cochlea produced slowly regenerative depolarizations or Na action potentials during current injection, whereas hair cells isolated from more basal regions usually produced voltage oscillations (ringing) in response to depolarizing current injection, an indication of electrical resonance. Resonant frequencies ranged from 50 to 157 Hz in different cells. The higher-frequency cells tended to have larger and more rapidly activating outward currents than did the lower-frequency cells. An inward Ca current and an outward Ca-activated K current were present in all hair cells. In addition, an inwardly rectifying current and a small, transient outward current were often seen. Thus, we conclude that an electrical tuning mechanism is present in alligator hair cells. The role of the ionic conductances in shaping hair cell responses to current injection, and the possible contributions of these electrical responses to cochlear function are discussed.

A mechanosensitive ion channel in the yeast plasma membrane

Mechanosensitive ion channels use mechanical energy to gate the dissipation of electrochemical gradients across cell membranes. This function is fundamental to physiological processes such as hearing and touch. In electrophysiological studies of ion channels in the plasma membrane of the yeast Saccharomyces cerevisiae, channels were observed that were activated by, and adapted to, stretching of the membrane. Adaptation of channel activity to mechanical stimuli was voltage-dependent. Because these mechanosensitive channels pass both cations and anions, they may play a role in turgor regulation in this walled organism.

The actions of L-glutamate at the postsynaptic membrane of the squid giant synapse

The actions of L-glutamate on the postsynaptic membrane of the squid giant synapse were investigated using two methods of application: ionophoresis and bath perfusion. Bath perfusion of 10 mmoll-1 sodium glutamate did not produce an appreciable depolarization of the postsynaptic membrane but reversibly blocked the neurally evoked postsynaptic potential (PSP). The postsynaptic membrane depolarized when L-glutamate was applied ionophoretically. The sensitivity to glutamate application was not uniform, but sharply localized to sites which may correspond to synaptic contacts made by branching colaterals from the postsynaptic axon. The relationship between membrane potential and amplitude of the glutamate-activated postsynaptic potential (PSP) examined under current-clamp conditions was linear over the voltage range studied (−110 to −60 mV) with an extrapolated reversal potential of −36 mV. The amplitude of the glutamate-activated PSP was reduced either by replacing Na+ in the external solution with Tris+ (Na+-free) or by raising the extracellular K+ concentration to 20 mmoll-1 and was abolished by removing both Na+ and Ca2+ from the bath solution. The PSP amplitude was insensitive to changes in the extracellular Mg2+ concentration. The extrapolated reversal potential of the glutamate PSP was shifted to more positive potentials in both Na+-free and raised-K+ bathing solutions and was unchanged by anion substitution. The depolarization induced by L-glutamate increased with increasing ionophoretic current and reached a maximum with large pulses. Double logarithmic plots of the coulomb dose-response relationship gave a limiting slope in the range 1.7-2.2, suggesting that two glutamate molecules are required for receptor activation. The time course of desensitization of the glutamate response was studied using a double-pulse method. The initial decrease in the ratio, PSP2/PSP1, is followed by a slower time-dependent recovery of the postsynaptic response with a time constant of 8.5 s. Prolonged perfusion of the squid giant synapse with concanavalin A failed to abolish desensitization of the glutamate-evoked PSP.

Permeability to various cations of the voltage-dependent sodium channel of isolated rat hippocampal pyramidal neurons

The permeability to various cations of the voltage-dependent sodium channel of isolated rat hippocampal pyramidal neurons was investigated under the voltage-clamp condition. The neurons were dispersed enzymatically and mechanically and perfused internally using a suction pipette technique. The permeability sequence, estimated from the reveral potential of the inward current was Li+ greater than Na+ greater than hydrazine+ greater than formamidine+ greater than guanidine+ greater than methylguanidine+ greater than monomethylamine+. Thus the ionic selectivity of the voltage-dependent sodium channel of rat central nervous system neurons is similar to that in the squid axon, myelinated frog nerve fiber and rat ventricle muscle.

A calcium-activated, nonselective cationic conductance in Aplysia silent neurons

We have previously reported the activation of a triphasic current response by calcium injection in voltage-clamped, nonbursting neurons of Aplysia californica. Present evidence indicates that the second phase, a delayed inward current that peaks 10-20 seconds after the end of the injection, is a calcium-activated, nonselective cationic conductance. It can be carried by both sodium and calcium, is not sensitive to chloride concentration changes, but is voltage sensitive, decreasing in amplitude with hyperpolarization.

Electrophysiological properties of the follicle wall in the pig ovary

The transmural potential difference and short-circuit current of the porcine Graafian follicle have been measured in an attempt to test whether antral fluid accumulates as a result of active transport of salt. The values obtained by mounting explants of follicle wall in Ussing chambers were close to zero and the specific electrical resistance was only 59 delta.cm2. The elemental composition of the follicular fluid was similar to that of ovarian venous plasma with the exception of follicular Na+ which was slightly more abundant. Bicarbonate concentrations were slightly lower in follicular fluids. These findings were interpreted as evidence that the follicular wall is a leaky epithelium and, therefore, any charge resulting from net ion transport will be shunted along low resistance paracellular pathways.

Properties of the kainate channel in rat brain mRNA injected Xenopus oocytes: ionic selectivity and blockage

The properties of kainate receptor/channels were studied in Xenopus oocytes injected with mRNA that was isolated from adult rat striatum and cerebellum and partially purified by sucrose gradient fractionation. Kainate (3-1000 microM) induced a smooth inward current that was competitively inhibited by gamma-D-glutamyl-aminomethanesulfonate (GAMS, 300 microM). In striatal mRNA-injected oocytes, the kainate current displayed nearly linear voltage-dependence and mean reversal potential (Er) of -6.1 +/- 0.5 mV. In cerebellar mRNA-injected oocytes; Er was nearly identical (-5.1 +/- 1.2 mV) but there was marked inward rectification of the kainate current. Ion replacement studies reveal that the kainate channel is selective for cations over anions, but relatively non-selective among small monovalent cations. Large monovalent cations such as tetrabutylammonium are impermeant and induce a non-competitive block of kainate current that is strongly voltage-dependent. Divalent cations are relatively impermeant in the kainate channel and Cd++ and other polyvalent metals were shown to block kainate current by a mechanism that is only weakly voltage-dependent. A model of the kainate channel is proposed based upon these observations.

Characterization of the ionic mechanism responsible for the hyperpolarization-activated current in frog sinus venosus

Voltage clamp experiments were carried out on the sinus venosus of the frog by means of the double mannitol gap technique. The ionic mechanism underlying the slowly hyperpolarization-activated inward current was investigated by changing the concentration and species of alkali cations and divalent cations in the bathing solution. Adding Rb or Cs in concentration of 10-20 mM to the control solution led to a dose-dependent increase in the inward current, as does elevating the external concentration of K from 2.5 to 25 mM. After the inward current had been nearly suppressed by completely substituting Tris for Na in the external medium, it was partially restored after a subsequent addition of K, Rb or Cs to the Na-free medium. Various alkaline earths or transition metals added to the bathing solution markedly depressed the magnitude of the inward current. This inhibitory effect varied with concentration and nature of divalent cations added. It also depended on the concentration and species of alkali cations present in the external solution. From these observations it was proposed that the conductance responsible for the inward rectification in frog sinus venosus does not discriminate among monovalent cations. The results support the existence of a weak-field-strength site located in the permeation pathway. Divalent cation may exert their inhibitory effect by competing with permeant ions for this site.

Cell membrane potential: a signal to control intracellular pH and transepithelial hydrogen ion secretion in frog kidney

The dependence of intracellular pH (pHi) and transepithelial H+ secretion on the cell membrane potential (Vm) was tested applying pH-sensitive and conventional microelectrodes in giant cells fused from single epithelial cells of the diluting segment and in intact tubules of the frog kidney. An increase of extracellular K+ concentration from 3 to 15 mmol/l decreased Vm from -49 +/- 4 to -29 +/- 1 mV while pHi increased from 7.44 +/- 0.04 to 7.61 +/- 0.06. Addition of 1 mmol/l Ba2+ depolarized Vm from -45 +/- 3 to -32 +/- 2 mV, paralleled by an increase of pHi from 7.46 +/- 0.04 to 7.58 +/- 0.03. Application of 0.05 mmol/l furosemide hyperpolarized Vm from -48 +/- 3 to -53 +/- 3 mV and decreased pHi from 7.47 +/- 0.05 to 7.42 +/- 0.05. In the intact diluting segment of the isolated-perfused frog kidney an increase of peritubular K+ concentration from 3 to 15 mmol/l increased the luminal pH from 7.23 +/- 0.08 to 7.41 +/- 0.08. Addition of Ba2+ to the peritubular perfusate also increased luminal pH from 7.35 +/- 0.07 to 7.46 +/- 0.07. Addition of furosemide decreased luminal pH from 7.32 +/- 0.03 to 7.24 +/- 0.05. We conclude: cell depolarization reduces the driving force for the rheogenic HCO3- exit step across the basolateral cell membrane. HCO3- accumulates in the cytoplasm and pHi increases. An alkaline pHi inactivates the luminal Na+/H+ exchanger. This diminishes transepithelial H+ secretion. Cell hyperpolarization leads to the opposite phenomenon. Thus, pHi serves as signal transducer between cell voltage and Na+/H+ exchange.

The effect of the cationic composition in perilymph upon the N1 latency of the guinea pig

Although a suitable cationic composition in perilymph is known to be essential for the generation of N1, the effect of the cationic change upon the N1 latency has never been investigated in detail. The scala tympani was perfused with an artificial perilymph with a high K+, low Na+ or low Ca2+ content, with simultaneous measurement by an ion-selective microelectrode to observe its effect upon the N1 latency. An excess of K+, a depletion of Na+ and a depletion of Ca2+ in perilymph individually suppressed the N1 amplitude and elevated the N1 threshold. The N1 latency was not prolonged in the high K+ group but the significant prolongation was observed in the other two groups.

Comparative ototoxicity of kanamycin A and kanamycin B in the guinea pig

It has previously been shown that simple compounds with multiple amine groups are ototoxic, the degree of ototoxicity depending on the number of amine groups in the molecule. The relationship between the number of amino groups and ototoxicity in aminoglycoside was studied using kanamycin A and kanamycin B, which contain 4 and 5 amino groups respectively. Forty-five pigmented guinea pigs were injected intratympanically with 0.1 ml of different concentrations of kanamycin A and kanamycin B. The animals were sacrificed 4 days after injection and the organ of Corti was studied by scanning electron microscopy. It was found that on an equimolar basis, kanamycin B (with 5 amino groups) is more cochleotoxic than kanamycin A (with 4 amino groups). The greater cochleotoxic potential of kanamycin B may be explained by the higher cationic nature of the molecule due to protonation of the amino--NH2 groups at physiological pH, resulting in a greater affinity between the drug and the cell membrane.

Ionic mechanisms underlying the firing properties of rat neonatal motoneurons studied in vitro

Ionic mechanisms underlying the firing properties of spinal motoneurons of neonatal rats (postnatal days 3-10) have been investigated using a hemisected, in vitro spinal cord preparation. These results demonstrate the presence of a high-threshold voltage-dependent calcium response and partial sodium-dependent spikes. The calcium current is evident during the falling phase of the action potential and is the major component of the after-depolarizing potential. The subsequent increase in intracellular calcium concentration activates a calcium-dependent potassium conductance (gK-Ca), the major component of the after-hyperpolarizing potential. The gCa, by activating gK-Ca, is the primary determinant of firing rate in neonatal motoneurons. For, when gCa was blocked by Cd2+, the interspike interval decreased, the maximum firing rate and the slope of the firing frequency-injected current relation increased. The calcium current is particularly robust during the first few postnatal days; during this period, tetrodotoxin resistant action potentials can be elicited by direct stimulation under control conditions. In animals older than 5 days such calcium spikes could be elicited only after decreasing gK with intracellular Cs+ or extracellular tetraethylammonium. This was the case even when 1 mM of the bath CaCl2 was replaced with BaCl2. The rising phases of calcium spikes recorded from neurons in both age groups demonstrate several components suggesting the calcium spikes comprise several discrete events, which probably originate across the dendritic membrane. When gK was decreased by bath application of tetraethylammonium+ and Cs+, neonatal motoneurons generated prolonged Ca-dependent spikes lasting for up to 6 s. Repolarization of Ca spikes occurred in two stages, the first was rapid (-2.11 +/- 0.8 V/s, n = 6) but incomplete. The second, was slower (-0.01 +/- 0.003 V/s, n = 5) and returned the membrane potential to the resting level after about 1-2 s. It is suggested that accumulation of extracellular potassium may contribute to the slow phase of repolarization. Motoneurons from the younger age group (3-5 days old) demonstrate all-or-none partial spikes rising from the after-depolarization of directly elicited sodium-dependent action potentials. Similar partial spikes were elicited from neurons from older animals during intracellular Cs+ loading. The partial spikes had faster rates of rise than the tetrodotoxin-resistant spikes and were not seen after tetrodotoxin treatment, suggesting that they are sodium-dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

The pharmacology of fever

The ability to minimise, if not prevent, large variations in deep body temperature that would otherwise result from some environmental conditions is a homeostatic function of unquestioned benefit that is demonstrated only by the more highly evolved animals. Nevertheless, body temperature is raised above normal values in many pathological conditions. This increase in temperature or fever is an active and co-ordinated response, which indicates the involvement of the CNS. Central injection and lesion studies have shown that the brain, in particular the PO/AH, is the site of action of fever-inducing agents, termed pyrogens. Electrophysiological data show that pyrogens modify the activity of central thermosensitive neurones as if to increase heat gain and decrease heat loss. The common response of fever to pyrogens of diverse origins is attributable to fever being mediated by an endogenous pyrogen released by phagocytic cells in the host. The mechanism by which central neuronal function is disturbed by pyrogens present in the periphery is not known. Tracer studies have yet to demonstrate the passage of a pyrogen across the blood-brain barrier. The possible involvement of several putative neurotransmitters and modulators in fever has been reviewed here, but most compounds have not been studied sufficiently to allow firm conclusions to be drawn. Much of the data is limited to the effects of the putative mediators on normal thermoregulation but, even when the effect is hyperthermia, such observations do not necessarily indicate a role for the endogenous material in fever. Dose-response curves for agonists and the effects of antagonists are often undetermined. This shortfall in data is due to some extent to the nature of fever; a central response in vivo over several hours. Although fever may enhance other host reactions to combat infection and inflammation, neither this benefit nor the undesirability of antipyretic therapy has been demonstrated unequivocally in either homeothermic laboratory animals or humans. Consequently, antipyretic drugs continue to be used clinically to alleviate the fever, malaise and/or pain commonly associated with disease. The drugs in common usage are the nonsteroidal antipyretic analgesics, many of which also have an anti-inflammatory effect. The primary mode of action of these drugs as antipyretics appears at present to be the inhibition of cyclo-oxygenase and a consequent reduction of prostanoid material in pyrogen-sensitive areas of the brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Hepatic bile flow

The hepatocyte is a polar cell that can remove a variety of molecules from blood and excrete them into bile. This review is primarily concerned with the mechanism of transport of the principal anions--the bile salts--across the sinusoidal membrane, their passage through the cell, and excretion across the canalicular membrane. Clearly much of this process is poorly understood, but the study of the membrane stages should be facilitated by the ability to prepare purified sinusoidal and canalicular membrane vesicles. For example, the relative importance of albumin-binding sites as well as the putative bile salt receptor proteins can be better assessed. It seems likely that although the interaction of bile salts with receptor proteins is important, it is an initial event that puts the bile salt in the correct place for uptake to occur. The driving force for uptake is the Na+ gradient created across the basolateral membrane by the activity of the Na+-K+-ATPase. Within the cell, various modes of transport have been suggested. Several authors emphasize the importance of protein binding of bile salts, either because of their presumed ability to maintain the concentration of these anions in the hepatocyte below their critical micellar concentration or because of their putative role in transport. It is important to understand these aspects of the role of cytosolic proteins for several reasons. Knowledge of the true concentration of free bile salt within the cell should allow estimation of whether the electrochemical gradient is sufficient for bile salts to accumulate in bile without the need for active transport of molecules from the cell into the canaliculus. The compartmental model described by Strange et al. (153) offers one theoretical way of determining the concentration of free bile salt, although the problems inherent in studying amphipath binding to the membranes of subcellular organelles (31) require that the model be reevaluated by the hygroscopic-desorption method. The second role suggested for the cytosolic bile salt-binding proteins is as transport proteins. As discussed in section VI, I think it is unlikely that the proteins identified so far act in this way, and it is more likely that movement occurs by diffusion in free solution. It is also important to determine the possible involvement of subcellular organelles such as Golgi bodies. Little is known of their role in the transport of bile salts or indeed where bile salt micelles are formed.(ABSTRACT TRUNCATED AT 400 WORDS)

Free fatty acids and (Na+,K+)-ATPase: effects on cation regulation, enzyme conformation, and interactions with ethanol

Effects of free fatty acids on parameters of (Na+,K+)-ATPase regulation related to enzyme conformation were examined. Sensitivity to inhibition by free fatty acid increased as the number of double bonds increased. Free fatty acids reduced affinity for K+ or Na+ at their regulatory sites without altering apparent K+ affinity at its high-affinity site, and increased apparent affinity for ATP. The apparent E2/E1 ratio and apparent delta H and delta S for the E1-E2 transition were reduced by fatty acid. High K+ or low temperature reduced the sensitivity of enzyme to inhibition by free fatty acid. In the presence of low K+, arachidonic acid potentiated inhibition of phosphatase activity by ethanol. Arachidonic acid alone had little effect on the rate of ouabain binding, but accelerated ouabain binding in the presence of K+. These data suggest that fatty acids alter (Na+,K+)-ATPase by preventing the univalent cation-mediated transition to E2, the K+-sensitive form of enzyme. (Na+,K+)-ATPase could potentially be influenced in vivo by free fatty acids released by phospholipases or during hypoxia, or by changes in membrane lipid saturation.

Structural and functional properties of DNA polymerase delta from rabbit bone marrow

DNA polymerase delta, the most recently described class of eukaryotic DNA polymerase, has been purified to apparent homogeneity from rabbit bone marrow. Unlike the previously known eukaryotic DNA polymerases, delta has a 3' to 5' exonuclease as an integral component of its 122 000 molecular weight, single polypeptide structure. Similar to the function with prokaryotic DNA polymerases, the 3' to 5' exonuclease assists DNA polymerase delta in maintaining the fidelity of DNA synthesis by excising misincorporated nucleotides. DNA polymerase delta and the longer known eukaryotic DNA polymerase alpha are similar in many features. Both are very sensitive to sulfhydryl inhibitors such as N-ethylmaliemide (NEM) and to the antibiotic aphidicolin. Such criteria distinguish alpha and delta from DNA polymerases beta and gamma. This has led to the conclusion that nuclear DNA replication, which is sensitive to NEM and aphidicolin, is carried out by DNA polymerase alpha. However, the similar sensitivity of delta to these reagents requires that the role of alpha and delta in nuclear DNA replication be further defined. In many features DNA polymerase delta is also similar to the viral induced DNA polymerases such as the Herpes simplex virus DNA polymerases which also have associated 3' to 5' exonuclease. Understanding of DNA synthesis and the mechanism of DNA replication fidelity in mammalian cells depends upon a further understanding of both DNA polymerases alpha and delta and the nature of the relationship they have to each other.

Permeability properties of chick myotube acetylcholine-activated channels

The acetylcholine-(ACh-)activated channels of chick myotubes were studied by the patch-clamp method. Single-channel amplitudes were measured over a wide range of potentials in solutions of cesium, arginine, and three small amines. Symmetrical, isotonic cesium solutions gave a linear I-V relationship with the single-channel conductance, gamma, of 42 pS at 11 degrees C. Dilutions of cesium by mannitol shifted the reversal potential 23.9 mV per e-fold change in internal cesium concentration. Selectivity, as defined by reversal potential criteria, depended on the molecular size of the permeant cation. The Q10 of gamma for the symmetrical isotonic cesium solutions as well as internal isotonic methylamine was 1.3-1.4. These properties are qualitatively similar to those seen at the ACh-activated channel of the frog neuromuscular junction. Partially substituting arginine for internal cesium depressed outward currents. 80 mM arginine acted equally well from the inside or the outside, as if arginine transiently blocks the ACh-activated channel in a current dependent way. Diluting internal cesium almost 10-fold, from 320 to 40 mM, increased the permeability of the channel calculated from Goldman-Hodgkin-Katz equations by almost threefold. Thus, cesium itself appears to block with a dissociation constant of 135 mM. Methylamine blocked the channel approximately as well as did cesium. Ammonia and ethylamine blocked the channel somewhat more than cesium. We conclude that (a) the channel is qualitatively similar to that of frog neuromuscular junction, (b) cations bind within the channel, and (c) arginine decreases channel conductance equally whether applied from the inside or the outside.

The role of a humoral Na+,K+-ATPase inhibitor in regulating precapillary vessel tone

In this review, we first present chronologically our evidence suggesting that a circulating Na+,K+-ATPase and Na+-K+ pump inhibitor in part regulates the mechanical activity of the muscle in the cardiovascular system. We then present the relevant findings from other laboratories. The evidence from our laboratories includes the observations that local hyperkalemia decreases small-vessel resistance and local hypokalemia increases small-vessel resistance and that these responses can be blocked by ouabain, a potent Na+,K+-ATPase inhibitor. Myocardial Na+,K+-ATPase and vascular Na+-K+ pump activities are decreased in animals with experimental low-renin hypertension, vascular Na+-K+ pump activity is decreased in animals following acute volume expansion, and these changes are associated with bioassay evidence for a Na+-K+ pump inhibitor in the plasma. The inhibitor appears to come from, or be influenced by, the anteroventral third ventricle (AV3V) area of the brain. It produces electrogenic depolarization of the vascular smooth-muscle cell and may inhibit norepinephrine uptake by adrenergic nerve terminals. The evidence from other laboratories includes the observations that there is (a) a pressor and vascular sensitizing agent in the plasma of animals and patients with low-renin hypertension, (b) reduced Na+-K+ pump activity in the leukocytes of some patients with essential hypertension, and (c) a Na+,K+-ATPase and Na+-K+ pump inhibitor in the plasma of some patients with essential hypertension.

Regulation of muscarinic agonist binding by cations and guanine nucleotides

EDTA treatment of membrane preparations from rat brain and myocardium reduced the relative proportion of superhigh and high affinity binding sites for muscarinic agonists by up to 60%. This effect was partially or completely reversed by millimolar concentrations of Mg2+ or Mn2+. A number of multivalent metal cations gave qualitatively similar effects, yielding stimulation of agonist binding at low concentrations but inhibition at higher concentrations. The divalent cation-linked subpopulation of muscarinic agonist binding sites identified in this study appears to be the primary target for guanine nucleotide inhibition.

Role of cations in olfactory reception

The effects of changed ionic environments on the olfactory responses in the carp, the rainbow trout, and the bullfrog were examined by recording the stimulant-induced waves from the olfactory bulb. (a) Application of stimulants (various species of amino acids and beta-ionone) dissolved in deionized water to the EDTA-treated olfactory epithelium of the carp did not induce any response. The addition of various species of salts to the stimulating solution reversibly restored the response. (b) The responses of the carp to L-alanine in the presence of MgCl2 and MgSO4 and those in the presence of KCl and K4Fe(CN)6 are described by single curves, respectively, as a function of concentration of the cations, suggesting that the cations support olfactory reception. (c) All the inorganic cations examined (Li+, NH3+, K+, Ca2+, Mg2+, Co2+, Mn2+, Cd2+) and organic cations (Tris+, choline+, bis-Tris propane2+) were effective to support the response of the carp, whereas TEA+, TBA+, triethanolamine+, and bis-Tris+ were ineffective. (d) The olfactory responses of the rainbow trout and the bullfrog were also reduced by removal of ions from the surface of the epithelia and recovered by addition of ions. (e) It is suggested that the cations do not act as current carriers across the apical olfactory cell membrane for the generation of the receptor potential.

Anion exchange and anion-cation co-transport systems in mammalian cells

Electroneutral anion transfer in the Ehrlich ascites tumour cell has been found to occur by two separate mechanisms. One is an exchange diffusion system with many similarities to that found in erythrocytes, e.g. saturation kinetics with 'self-inhibition', a relatively pronounced temperature dependence, competitive interactions of Br-, NO3- and SCN-, and a low conductive PCl- of 4 x 10(-8) cm s-1. The main differences are that the Cl- flux in Ehrlich cells at 38 degrees C is one thousandth of the flux in red cells, and that the specificity of the system is less pronounced. It is suggested that the density of anion exchange sites in Ehrlich cells could be the same as in red blood cells, but with a lower turnover rate. The other system is an anion-cation co-transport system capable of mediating a secondary active Cl- influx. This system has a volume-regulatory function and is activated by a reduction in cell volume and intracellular [Cl-]. The two transport systems can be separated by using DIDS as an inhibitor of anion exchange and bumetanide as an inhibitor of co-transport. Under normal steady-state conditions Cl- flux is dominated by the exchange system. It is suggested that intracellular pH regulation can be achieved by the two systems operating in parallel, because the chloride disequilibrium maintained by the co-transport system can drive an influx of bicarbonate through the exchange mechanism.

Vascular smooth muscle in hypertension

The cause of the elevated arterial pressure in most forms of hypertension is an increase in total peripheral resistance. This brief review is directed toward an assessment of recent investigations contributing information about the factors responsible for this increased vascular resistance. Structural abnormalities in the vasculature that characterize the hypertensive process are 1) changes in the vascular media, 2) rarefication of the resistance vessels, and 3) lesions of the intimal vascular surface. These abnormalities are mainly the result of an adaptive process and are secondary to the increase in wall stress and/or to pathological damage to cellular components in the vessel wall. Functional alterations in the vascular smooth muscle are described as changes in agonist-smooth muscle interaction or plasma membrane permeability. These types of changes appear to play a primary, initiating role in the elevation of vascular resistance of hypertension. These alterations are not the result of an increase in wall stress and they often precede the development of high blood pressure. The functional changes are initiated by abnormal function of neurogenic, humoral, and/or myogenic changes that alter vascular smooth muscle activity.

Guanine nucleotide and cation regulation of the binding of [3H]cyclohexyladenosine and [3H]diethylphenylxanthine to adenosine A1 receptors in brain membranes

Guanine nucleotides, divalent cations, and sodium differentially regulate agonist and antagonist binding to adenosine A1 receptors in brain membranes. Guanine nucleotides decrease the binding of the adenosine A1 receptor agonist [3H]N6-cyclohexyladenosine ([3H]CHA) to guinea pig and bovine brain membranes by about 50% at 1--3 microM, while not affecting binding of the antagonist [3H]1,3-diethyl-8-phenylxanthine ([3H]DPX) to A1 receptors in bovine brain. GTP decreases the potency of agonists competing for [3H]DPX binding by 3--6 times, without altering the potency of antagonists. This effect can be used to grade experimental substances along an adenosine agonist-antagonist continuum. The 66% inhibition of [3H]CHA binding by 1 mM EDTA, with no change in [3H]DPX binding, suggests that endogenous divalent cations may regulate adenosine receptor interactions. Removal of endogenous divalent cations by EDTA treatment greatly increases the enhancement of [3H]CHA binding by divalent cations. Specific binding of [3H]CHA to guinea pig brain is increased 150--170% by 0.3--1.0 mM Mn2+, Mg2+, and Ca2+ following EDTA preincubation, secondary to an increase in apparent affinity and receptor number. Sodium ions also selectively regulate the binding of [3H]CHA. Sodium decreases [3H]CHA binding 40%, whereas lithium and potassium are ineffective. Sodium does not affect [3H]DPX binding.

Calcium-dependent and calcium-independent adhesive mechanisms are present during initial binding events of neural retina cells

The hypothesis that intercellular adhesion can be subdivided into two separable phenomena, an initial recognition event and a subsequent stabilization, is supported by the use of a new cell binding assay that provides a quantitative measure of intercellular binding strengths. Radioactive single cells are brought into contact with cell monolayers at 4 degrees C in sealed compartments. The compartments are inverted and a centrifugal force is then applied tending to dislodge the probe cells from the monolayers. By varying the speed of centrifugation, the force maintaining association between embryonic chick neural retina cells was determined to be on the order of 10(-5) dynes after incubation at 4 degrees C. Brief incubations at 37 degrees C resulted in significant strengthening of the intercellular bond. Using this cell binding assay, neural retina cells were shown to exhibit both a Ca++-independent and a Ca++-dependent mechanism in their initial binding to one another.

Electrogenic sodium pump in rabbit atrio-ventricular node cell

Electrogenicity of the Na pump was demonstrated in rabbit A-V node cells by analyzing the K-induced hyperpolarization occurring after a short period of K-free perfusion. The transient hyperpolarization was abolished completely by strophanthidin (10(-5)M). The membrane slope conductance remained unchanged during the transient hyperpolarization. On perfusion of 50 mM K and K-free incubation the transient hyperpolarization reached --69 mV which was more negative than the expected EK (about --28 mV). The order of potencies of monovalent cations to activate the K site of the Na pump was Tl greater than Rb equal to K greater than NH4 equal to Cs greater than Li, which was similar to the sequence reported in the literature. Michaelis-Menten type activation of the K site of the Na pump was suggested from the relationship between the decay rate constant of the K-induced outward current transient and [K]o. These findings obviously indicate that the Na pump in the A-V node cells shares common characteristics with those of other excitable tissues. Direct contribution of the pump activity to the membrane potential under physiological conditions was suggested by a significant depolarization occurring immediately after application of strophanthidin.

Sodium-coupled taurocholate transport in the proximal convolution of the rat kidney in vivo and in vitro

Using the standing droplet technique in the renal proximal convolution and simultaneous microperfusion of the peritubular capillaries, the zero net flux transtubular concentration difference of taurocholate (DeltaC(TC-)) at 45 s was determined as a measure of active bile acid reabsorption in vivo. Starting with 0.1 mmol/liter taurocholate in both perfusates the control DeltaC(TC-) of 0.042 mmol/liter fell to 0.006 mmol/liter (P < 0.001) when the Na(+) concentration in the perfusates was reduced to zero. Removal of bicarbonate from the perfusates to alter pH had no influence on DeltaC(TC-). When glycocholate was added to the perfusates DeltaC(TC-) was decreased, while probenecid increased DeltaC(TC-). These observations were extended by studies performed with brush border membrane vesicles derived from renal cortex. The initial (20 s) uptake of 0.01 mmol/liter taurocholate in the presence of a Na(o) (+) > Na(i) (+) gradient was stimulated twofold compared with its uptake in the absence of a Na(+) gradient. Uptake of taurocholate was osmotically and temperature sensitive. Membranes preloaded with unlabeled glycocholate showed accelerated entry of labeled taurocholate (trans-stimulation) only in the presence of Na(+). Replacement of Na(+) in the media with K(+), Li(+), and choline(+) decreased initial taurocholate uptake by 49, 53, and 62%, respectively. Stimulation of taurocholate transport by cation gradient diffusion potentials was unlikely inasmuch as the addition of valinomycin under K(+) gradient conditions had no effect. A transmembrane pH gradient (pH(o) < pH(i)) did not influence initial uptake of taurocholate. Finally, in the presence of Na(+) taurocholate transport showed cis-inhibition with unlabeled bile acids and saturation kinetics with respect to increasing taurocholate concentrations. The micropuncture and vesicle data indicate that the net transport of taurocholate in the proximal tubule is the result of an electroneutral Na(+)-taurocholate cotransport across the brush border membrane.

Importance of spermatozoal zinc as temporary inhibitor of sperm nuclear chromatin decondensation ability in man

Nuclear chromatin decondensation (NCD) of ejaculated human spermatozoa was studied in vitro. Spermatozoa subjected to membrane disintegration induced by the detergent sodium dodecyl sulphate (SDS) were found to undergo NCD if previously or afterwards treated with substances known to deplete the spermatozoa of zinc (albumin and EDTA). Zn2+, but not other, "prostatic" cations (Ca2+, Mg2+), inhibited the experimentally induced NCD and the NCD of spermatozoa from men with impaired prostatic function. It is suggested that the human spermatozoon has an intrinsic mechanism for NCD, that is preserved by temporary zinc inhibition and might be reactivated by zinc removal within the female genital tract.

Partial characterization of a phosphoryl group transferring enzyme in the membrane of catecholamine storage vesicles

Phosphoryl group transfer from ATP to ADP occurred in the isolated membrane of catecholamine storage vesicles. The reaction was accelerated by extraction of the membranes with 50% (v/v) acetone and by treatment with 1% (v/v) Triton X-100. The phosphoryl group transfer reaction was activated by Mg2+ and by Mn2+. The activation profile differed from that obtained for the ATPase activity. The Michaelis-Menten kinetics of the phosphoryl transfer reaction were not entirely linear. From the linear parts of the double reciprocal plots KmATP approximately equal to 1 mM and KmADP approximately equal to 0.4 mM was obtained. All lines of the double reciprocal plots intersected indicating a sequential reaction mechanism. The reaction exhibited a narrow specificity for nucleoside diphospate and a broader one for nucleoside triphosphate indicating that ADP was the true substrate. The transfer reaction was slightly inhibited by AMP, orthophosphate and P1, P5-di(adenosine-5')pentaphosphate. The thiol reagents, N-ethylmaleimide and para-chloromercuribenzoate (PCMB), affected the ATPase activity and the phosphoryl transfer activity differently: with the blockade of 2.4 essential thiol equivalents by N-ethylmaleimide the ATPase was inhibited 50% and net uptake of catecholamine ceased, while the phosphoryl transfer remained unimpaired. PCMB affected both, the ATPase activity and phosphoryl transfer reaction. Treatment of the membranes with dithioerythritol prevented the PCMB-induced inhibition of the phosphoryl transfer, but was ineffective in protecting the ATPase activity, indicating that different thiol groups must be involved in the both enzymatic activities.

Modification of intramuscular pH oscillations in the isolated perfused rat heart by different interventions

Changes in the intramuscular pH oscillations were examined by the use of an antimony electrode upon perfusing the isolated rat heart under different experimental conditions. The pH oscillations were decreased upon perfusing the hearts with Na+- or Ca2+-free medium and increased upon perfusing with K+-free medium. Increasing the temperature of perfusion medium from 25 to 40 degrees C or omitting glucose from the perfusing medium decreased the magnitude of oscillations. On the other hand, complete interruption of the perfusion flow resulted in an increase in the amplitude of pH oscillation. An initial increase followed by a decrease in the pH oscillation was seen when hearts were perfused with medium containing lactic acid at pH 6.6. These results suggest that pH oscillations reflect fluctuations in myocardial metabolism.