Uric acid contributes greatly to hepatic antioxidant capacity besides protein

Uric acid is the end-product of purine nucleotide metabolism and an increase in uric acid concentration in the body results in hyperuricemia, ultimately leading to gout. However, uric acid is a potent antioxidant and interacts with reactive oxygen species (ROS) to be non-enzymatically converted to allantoin. Uric acid accounts for approximately 60 % of antioxidant capacity in the plasma; however, its contribution to tissue antioxidant capacity is unknown. In this study, the contribution of uric acid to tissue antioxidant capacity and its conversion to allantoin by scavenging ROS in tissue were examined. The results showed that a decrease in hepatic uric acid content via allopurinol administration significantly reduced hepatic total-radical trapping antioxidant parameter (TRAP) content in protein-free cytosol. Additionally, treating protein-free cytosol with uricase led to a further reduction of hepatic TRAP content. Allantoin was also detected in the solution containing protein-free cytosol that reacted with ROS. These findings suggest that in the absence of protein, uric acid contributes greatly to antioxidant capacity in the liver, where uric acid is converted to allantoin by scavenging ROS.

Excitatory effects of ATP on rat dorsomedial hypothalamic neurons

We investigated P2X purinoceptors in rat dorsomedial hypothalamic (DMH) neurons using nystatin-perforated patch-clamp recordings and fura-2 microfluorometry. Adenosine triphosphate (ATP) concentration-dependently evoked an inward current and increased cytosolic Ca(2+) ([Ca](i)). The rise in [Ca](i) was dependent on external Ca(2+) and Na(+), was blocked by Ca(2+) channel antagonists and had pharmacological properties consistent with P2X2 receptors. These results suggest that P2X receptor-mediated depolarization activates voltage-gated Ca(2+) channels, resulting in an increase in [Ca](i).

Excitatory effect of ATP on acutely dissociated ventromedial hypothalamic neurons of the rat

The ATP-induced increase in the cytosolic Ca(2+) concentration ([Ca]i) and current in acutely dissociated ventromedial hypothalamic rats neurons were investigated using fura-2 microfluorometry and the nystatin-perforated patch recording method, respectively. The ATP-induced [Ca]i increase was mimicked by dimethyl-thio-ATP and ATPgammaS, and was inhibited by P2 purinoreceptor antagonists. The ATP-induced [Ca]i increase was markedly reduced by removal of external Na(+) or Ca(2+), and by addition of various Ca(2+) channel antagonists. ATP induced a transient inward current exhibiting a strong inward rectification at membrane potentials more positive than -20 mV. The ATP-induced current at a holding potential of -70 mV was concentration-dependent with a half-maximum effective concentration of 26 microM. Increasing the external Ca(2+) concentration to 10 mM shifted the dose-response relationship to the right. ATP induced only a small current and a small increase in [Ca]i, even at 10 mM Ca(2+), when external Na(+) was removed, suggesting the relatively low permeability to Ca(2+) of purinoceptor channels. These results suggest that ATP activates non-selective cation channels by acting on P2X purinoceptors on dissociated ventromedial hypothalamic neurons, which in turn increases [Ca]i by increasing Ca(2+) influx through voltage-dependent Ca(2+) channels.

Functional expression of cholecystokinin-A receptor on ventromedial hypothalamic neurons in the immature rat brain

Cholecystokinin-8 (CCK-8) dose-dependently increased the cytosolic Ca2+ concentration ([Ca]i) in ventromedial hypothalamic neurons acutely dissociated from the immature rat brain. The CCK-8 response was mimicked by caerulein, but not by CCK(B) agonists, and was often inhibited by CCK(A) receptor antagonists, but rarely by CCK(B) receptor antagonists. The response was dependent on external Ca2+ and Na+, and was inhibited by voltage-dependent Ca2+ channel blockers. The results suggest that CCK-8-induced depolarization via CCK(A) receptors increased Ca2+ influx through a voltage-dependent Ca2+ channel, which in turn increased [Ca]i.

Activation of ATP receptor increases the cytosolic Ca(2+) concentration in nucleus accumbens neurons of rat brain

ATP increased the cytosolic Ca(2+) concentration ([Ca](i)) in nucleus accumbens neurons acutely dissociated from rat brain. The ATP response was dependent on external Ca(2+) and Na(+), and was blocked by voltage-dependent Ca(2+) channel blockers. The results suggest that the ATP-induced depolarization increases Ca(2+) influx resulting in the increase in [Ca](i).

Comparisons between hemodynamics, during and after bathing, and prognosis in patients with myocardial infarction

The purpose of this study was to establish the safest way to bathe patients with myocardial infarction (MI) through measuring the hemodynamics during and after bathing. Seventy patients with MI were bathed supine in a Hubbard tank filled with 42 degrees C tap water for 5 min. The subjects were divided into 2 groups depending on their hemodynamic values 10 min after bathing: pulmonary capillary wedge pressure unchanged even after bathing (group A), and decreased pressure after bathing (group B). The left ventricular ejection fraction of group B was significantly higher than that of group A: 53.6% vs. 39.7%, respectively (p<0.01). The physical work capacity of group B was significantly higher at 5.6 METs, than that of group A with 4.5 METs (p<0.05). During the average of their 37-month follow-up period, there were 3 cardiac events in group B and 6 in group A. There were 2 cardiac events during bathing, both of which occurred in group A. When patients with MI take a bath, it is essential to closely monitor them, especially to those patients with lower cardiac function, because they have a higher possibility of a cardiac event.

Excitatory effect of Cd2+ on cat adrenal chromaffin cells

To understand the mechanism(s) underlying the Cd2+- and Co2+-induced increases in the cytosolic free Ca2+ concentration ([Ca]i) in cat adrenal chromaffin cells, we used nystatin-perforated patch recording method and fura-2 microfluorometry. Under the current-clamp conditions, the external application of 5x10(-7) M Cd2+ slowly depolarized the cells resulting in the bursting of action potentials. Under the voltage-clamp conditions, Cd2+ evoked a slow inward current accompanied by a decrease of K+ conductance at a holding potential of -40 mV, and Co2+ mimicked Cd2+ action. In some cells (16%), Cd2+ evoked an additional rapid transient outward current associated with an increased K+ conductance and a successive slow inward current. The Cd2+-induced inward current was activated in a concentration-dependent manner with a half-maximum concentration of 9.3x10(-8) M. The Cd2+- and Co2+-induced [Ca]i increases measured with fura-2 microfluorometry were maximal at 10(-6) and 10(-5) M, respectively, and the higher concentrations of both cations caused the smaller responses. Additional transient increase in [Ca]i was often evoked upon the removal of relatively higher concentrations of these metals. It was concluded that the Cd2+-induced membrane depolarization due to the decrease in K+ conductances evoked the bursting firings resulting in the increase in [Ca]i, and consequently might stimulate the catecholamine secretion.

Detection of human T-lymphotropic virus type I p40tax protein in cerebrospinal fluid cells from patients with human T-lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis

We investigated the role of viral transcripts of human T-lymphotropic virus type I (HTLV-I) in the cerebrospinal fluid (CSF) cells and peripheral blood mononuclear cells (PBMCs) of patients with human T-lymphotropic virus type I-associated myelopathy (HAM)/tropical spastic paraparesis (TSP). To detect the HTLV-I p40tax protein, we developed a new sensitive method of immunohistochemistry combined with tyramide signal amplification and quantitative analysis. Seven patients with HAM/TSP were examined. As controls, four patients with other neurological diseases were examined; two of these patients were infected with HTLV-I and the other two were not. Both the CSF cells and PBMCs were reacted with a monoclonal antibody, Lt-4, for p40tax protein, followed by secondary antibody labeled with horseradish peroxidase. This was visualized by fluorescein directly labeled with tyramide and the number of positive cells was quantified with a Laser Scanning Cytometer. In the samples from patients with HAM/TSP, the HTLV-I p40tax protein was successfully detected by tyramide signal amplification, but not without it. In HAM/TSP patients, 0.04-1.16% of the CSF cells and 0.02-0.54% of PBMCs were positive for the HTLV-I p40tax protein, respectively. The expression of the HTLV-I p40tax protein in the CSF cells was more frequent than that in PBMCs in both HAM/TSP patients and HTLV-I carriers, and was also more frequent in the patients with HAM/TSP of shorter duration of illness. This technique could be a powerful tool to investigate the pathogenic mechanism of diseases associated with HTLV-I.

Sequestration of depolarization-induced Ca2+ loads by mitochondria and Ca2+ efflux via mitochondrial Na+/Ca2+ exchanger in bovine adrenal chromaffin cells

We used fura-2 microfluorometry to investigate the role of mitochondria in regulating the increase in the cytosolic Ca2+ concentration ([Ca]in) and the mechanism(s) underlying the subsequent Ca2+ efflux from mitochondria in bovine adrenal chromaffin cells. The rate of [Ca]in decay during and following stimulation with 100 mM KCl depolarization was markedly increased when the mitochondrial Na+/Ca2+ exchanger was inhibited by clonazepam or CGP-37157(CGP). In contrast, the addition of gramicidin, which increased the cytosolic Na+ concentration, following KCl depolarization caused a secondary increase in [Ca]in. This secondary increase in [Ca]in was prevented by the addition of clonazepam or CGP, and by the removal of external Na+. The subsequent removal of clonazepam or CGP, or the delayed addition of Na+ caused a slow increase in [Ca]in. A protonophore (FCCP) applied following KCl depolarization also caused a robust, secondary increase in [Ca]in, which was insensitive to blocking by clonazepam or CGP. Neither gramicidin nor FCCP altered the [Ca]in decay when applied following stimulation with histamine or caffeine, which mobilized Ca2+ from intracellular stores. These results suggest that the large [Ca]in increase induced by Ca2+ influx, but not by intracellular Ca2+ release, is buffered by mitochondria, and that the mitochondrial Na+/Ca2+ exchanger makes a major contribution to the subsequent Ca2+ efflux from mitochondria.

Cd2+ and Co2+ at micromolar concentrations mobilize intracellular Ca2+ via the generation of inositol 1,4,5-triphosphate in bovine chromaffin cells

To understand the mechanisms underlying the Cd2+- and Co2+-induced intracellular Ca2+ mobilization, we measured the levels of inositol phosphates using bovine chromaffin cells. Studies using HPLC indicated that Cd2+, Co2+ and methacholine significantly increased the generation of 1,4,5-IP3. The results suggest that Cd2+ and Co2+ mobilize Ca2+ from IP3-sensitive Ca2+ stores, possibly through the presumptive Cd2+ receptor.

An established hybridoma clone producing a monoclonal antibody against Vibrio anguillarum

Vibrio anguillarum is a pathogenic microorganism of vibriosis, an infectious disease found in various fish species. A mouse hybridoma clone, named C5, that produced a monoclonal antibody to V. anguillarum was established. The specific reaction of C5 antibody with V. anguillarum was confirmed by the pre-adsorption effect of the V. anguillarum cells in ELISA and a cell immunoprecipitation experiment. Western blotting analysis indicated that the C5 antibody recognized a high molecular weight substance extracted from cells with detergents.

Hemodynamic effects of warm bathing in a Hubbard tank and exercise loading in patients after myocardial infarction

Hemodynamic parameters were measured during bathing and exercise testing in 43 patients with myocardial infarction (mean age: 60.2 years) to investigate the predictive parameters to determine when patients could safely resume bathing. Patients took a fresh water bath at 42 degrees C in the supine position for 5 min in a Hubbard tank. Group A showed an elevation of pulmonary capillary wedge pressure (PCWP) during bathing of 10 mmHg or more (23 patients, mean age: 61.7 years) and group B showed an elevation of less than 10 mmHg (20 patients, mean age: 60.5 years). Continuous multistep exercise tests were performed with a bicycle ergometer in the supine position, and hemodynamic parameters were measured at up to 50 W for 3 min on the day before the warm bathing test. There were no significant differences in the changes of arterial pressure and heart rate between the two groups. The PCWP at 3 min with a load of 50 W was significantly higher in group A (26.9 +/- 9.0 mmHg) than in group B (16.7 +/- 9.1 mmHg, p < 0.01). The stroke index (SI) during exercise testing was significantly lower in group A than in group B. The difference in the stroke index from baseline values (delta SI) at 3 min with a load of 50 W was significantly lower in group A (3.5 +/- 5.5 ml/m2/beat) than in group B (10.6 +/- 7.0 ml/m2/beat, p < 0.01). Similarly, delta CI and delta oxygen pulse during testing were significantly lower in group A than in group B. The physical work capacity and ejection fraction of the left ventricle of group A were significantly lower than those of group B, whereas the left ventricular end-diastolic pressure was higher in group A than in group B. CI, delta CI, SI, delta SI, METs, oxygen pulse, and delta oxygen pulse were examined by regression analysis and multivariate analysis to predict a significant elevation of delta PCWP during bathing. delta SI (p = 0.0032), delta CI (p = 0.0094), delta SI + METs (p = 0.0051), delta CI + METs (p = 0.0061), delta CI + delta SI (p = 0.0084), and delta CI + delta SI + METs (p = 0.0093) showed the highest correlations with delta PCWP. These findings suggest that changes in delta CI, delta SI, and METs are good predictive parameters for determining when patients may safely resume bathing. We suggest that patients with myocardial infarction, reduced cardiac function and a physical work capacity of approximately 4.0 METs, delta SI: 5 ml/m2/beat and delta CI: 2.4 l/min/m2 resume bathing only after careful consideration.

Mechanisms of GABA- and glycine-induced increases of cytosolic Ca2+ concentrations in chick embryo ciliary ganglion cells

We used fura-2 microfluorometry and the gramicidin-perforated patch clamp technique in an attempt to clarify the mechanisms underlying the GABA- and glycine-induced increases in the cytosolic Ca2+ concentration ([Ca]in) in acutely isolated chick embryo ciliary ganglion neurons. GABA, glycine, and isoguvacine, but not baclofen, increased [Ca]in in a dose- and a Ca2+-dependent manner. The GABA-induced [Ca]in increase was inhibited by bicuculline and picrotoxin, and potentiated by pentobarbital, flunitrazepam, and alphaxalone, whereas the glycine-induced [Ca]in increase was inhibited by strychnine but not by bicuculline or picrotoxin. L- and N-type Ca2+ channel blockers inhibited the GABA- and glycine-induced [Ca]in increases, whereas Bay K-8644 potentiated these responses. These responses were also substantially potentiated by blockers of various K+ channels and by lowering the external Cl- concentrations. The high KCI- and nicotine-induced [Ca]in increases were substantially reduced during continuous stimulation with either 2 microM GABA or 1 mM glycine. Electrophysiological studies indicated that the reversal potential of the GABA-induced current exhibited a more depolarized value than the resting membrane potential in 17 of the 25 cells examined. Taken together, these results suggest that both GABA and glycine depolarize the membrane potentials by increasing Cl- conductance via respective receptors and thus increase the Ca2+ influxes through L- and N-type voltage-dependent Ca2+ channels.

Muscarinic receptor agonist-induced increases in cytosolic Ca2+ concentrations in chick ciliary ganglion cells

We used fura-2 microfluorometry to examine the mechanism underlying the muscarinic receptor agonist-induced increase in the cytosolic Ca2+ concentration ([Ca]in) in acutely isolated chick ciliary ganglion neurons. The order of potencies of muscarinic agonists in increasing [Ca]in was: oxotremorine M > muscarine > methacholine > oxotremorine > bethanechol. The muscarine-induced increase in [Ca]in persisted after treatment with thapsigargin, which blocked caffeine- and muscarinic agonist-induced Ca2+ release. The muscarine-sensitive [Ca]in increase was inhibited by both L- and N-type Ca2+ channel blockers but potentiated by an L-type Ca2+ channel agonist. Muscarine was effective in increasing [Ca]in in the presence of a desensitizing concentration of nicotine, and simultaneous addition of maximal doses of muscarine and nicotine caused an additive increase in [Ca]in. On the other hand, nicotine-, ATP-, and high K(+)-induced increase in [Ca]in was markedly potentiated during continuous stimulation with muscarine. These results suggest that muscarinic receptor stimulation increases Ca2+ influx passing through voltage-dependent Ca2+ channels. However, the muscarine-induced Mn2+ influx was observed in only some muscarine-sensitive cells, suggesting that muscarine-induced depolarization is too weak to overcome the inhibitory effect of Mn2+ on Ca2+ channels.

Mechanism underlying the ATP-induced increase in the cytosolic Ca2+ concentration in chick ciliary ganglion neurons

We examined the mechanism underlying the ATP-induced increase in the cytosolic Ca2+ concentration ([Ca]in) in acutely isolated chick ciliary ganglion neurons, using fura-2 microfluorometry. The ATP-induced increase in [Ca]in was dependent on external Ca2+, was blocked in a dose-dependent manner by reactive blue 2, and was substantially inhibited by both L- and N-type Ca2+ channel blockers. ATP was effective in increasing [Ca]in in the presence of a desensitizing concentration of nicotine (100 microM), and simultaneous addition of maximal doses of ATP and nicotine caused an additive increase in [Ca]in, suggesting that ATP acts on a site distinct from nicotinic acetylcholine receptors. ATP also increased the cytosolic Na+ concentration as determined by sodium-binding benzofuran isophthalate microfluorometry. These results suggest that ATP increases Na+ influx through P2 purinoceptor-associated channels resulting in membrane depolarization, which in turn increases Ca2+ influx through voltage-dependent Ca2+ channels. However, ATP still caused a small increase in [Ca]in under Na+-free conditions, and this [Ca]in increase was little affected by Ca2+ channel blockers. ATP also increased Mn2+ influx under Na+-free conditions, as indicated by quenching of fura-2 fluorescence. These results suggest that nonselective cationic channels activated by ATP are permeable not only to Ca2+ but also to Mn2+, in addition to monovalent cations.

Pharmacology of nicotine-induced increase in cytosolic Ca2+ concentrations in chick embryo ciliary ganglion cells

Chick embryo ciliary ganglion cells were acutely isolated, and the mechanism(s) underlying the increase in the cytosolic Ca2+ concentration ([Ca]in) induced by high concentrations of nicotine examined using fura-2 microfluorometry. The order of potencies of nicotinic receptor agonists in increasing [Ca]in was ACh > nicotine = dimethylphenylpiperazinium > cytisine. The nicotine-induced increase in [Ca]in was inhibited not only by nicotinic antagonists but also by muscarinic antagonists, while the muscarine-induced [Ca]in increase was little affected by nicotinic antagonists. The nicotine-induced [Ca]in increase was inhibited by both L- and N-type Ca2+ channel blockers and potentiated by an L-type Ca2+ channel agonist, Bay-K-8644. Nicotine also increased the cytosolic Na+ concentration ([Na]in) as measured by sodium binding benzofuranisophthalate microfluorometry, and this [Na]in increase was inhibited by various agents which reportedly affected nicotinic receptor channels in adrenal chromaffin cells. These results suggest that nicotine increased Na+ influx through nicotinic receptor channels resulting in membrane depolarization, which in turn increased Ca2+ influx through voltage-dependent Ca2+ channels. However, nicotine still increased influxes of Ca2+ and Mn2+ in the absence of external Na+, suggesting that nicotinic receptor channels in these cells are permeable not only to monovalent cations but also to Ca2+ and Mn2+.

ATP responses in the embryo chick ciliary ganglion cells

The ATP responses in ciliary neurons acutely dissociated from chick ciliary ganglia were investigated using the nystatin perforated patch recording mode. ATP induced a transient inward current at a holding potential of -50 mV in a concentration-dependent manner. The half-maximum effective concentration of ATP was 8.2 microM and the Hill coefficient was 0.9. The current-voltage relationship of the ATP response revealed a strong inward rectification at potentials more positive than -30 mV and the reversal potential was near 0 mV. The relative potencies of purinoceptor agonists were in the order of ATP > 2-methylthio-ATP > ADP. Neither adenosine, AMP nor alpha, beta-methylene-ATP induced any response. The ATP-induced inward current was blocked by suramin, a selective P2 purinoceptor antagonist, in a concentration-dependent manner. The half-maximum inhibitory concentration was 4.5 microM. The cytosolic Ca2+ concentration was increased by ATP and suramin inhibited the increase in a concentration-dependent manner. These results suggest that ATP operates non-selective cation channels by acting on P2y purinoceptors and has a role in the excitation of ciliary neurons.

Nicotinic and muscarinic acetylcholine responses in the embryo chick ciliary ganglion cells

Nicotinic and muscarinic acetylcholine (ACh) responses were investigated in acutely dissociated chick ciliary ganglion neurons using the nystatin perforated patch clamp technique. ACh-induced a rapid transient inward current in 100% of the neurons at a holding potential of -60 mV. This rapid inward current was mimicked by nicotine but not by muscarine. The reversal potential of the rapid inward current was +10.5 mV and the current was inhibited by d-tubocurarine and hexamethonium in a dose-dependent manner. In 57.6% of neurons, a slow inward current was also induced by ACh at a holding potential of -20 mV. This slow inward current was mimicked by muscarine but not by nicotine. The slow inward current became smaller at a hyperpolarized potential but not reversed, being consistent with the fact that this current was elicited by the inhibition of M-current. p-Fluorohexa-hydrosiladifenidol (P-F-HHSiD) strongly inhibited the slow inward current, suggesting that the current was elicited by the activation of M3 receptors.

Cd2+ and Co2+ at micromolar concentrations stimulate catecholamine secretion by increasing the cytosolic free Ca2+ concentration in cat adrenal chromaffin cells

Cd2+ and Co2+ at micromolar concentrations increased the cytosolic free Ca2+ concentration, which was measured by fura-2 microfluorometry, in cat adrenal chromaffin cells. Simultaneously, these divalent cations stimulated catecholamine secretion from the perfused adrenal. The present findings suggest that these cations increase the Ca2+ influx by depolarizing the cell membrane and consequently stimulate catecholamine secretion.

Inability of Ca2+ influx through nicotinic ACh receptor channels to stimulate catecholamine secretion in bovine adrenal chromaffin cells: studies with fura-2 and SBFI microfluorometry

The concentration of cytosolic Ca2+ ([Ca]in) and catecholamine (CA) secretion were examined in bovine adrenal chromaffin cells to determine whether Ca2+ influx through nicotinic ACh receptor (nAChR) channels contributes to CA secretion induced by nAChR stimulation. Nicotine added under Na(+)-free conditions caused a marked increase in [Ca]in and quenching of fura-2 fluorescence in the presence of Mn2+, suggesting the stimulated entry of divalent cations through nAChR channels. However, nicotine-induced increase in CA secretion occurred only at a non-physiologically high external Ca2+ concentration under Na(+)-free conditions. Both the nicotine-induced increase in [Ca]in and CA secretion under Na(+)-free conditions were reduced in the presence of hexamethonium, methoxyverapamil (D600), nifedipine, Bay-K-8644, clonidine, and guanethidine. All of these agents inhibited the nicotine-induced increase in cytosolic Na+ concentration in a dose-dependent manner, as measured by SBFI microfluorometry. The present results suggest that Ca2+ influx through nAChR channels under physiological conditions may not contribute to CA secretion.

Caffeine- and muscarinic receptor agonist-sensitive Ca2+ stores in chick ciliary ganglion cells

To investigate the presence and the role of intracellular Ca2+ stores in chick ciliary ganglion cells, the concentration of cytosolic free Ca2+ ([Ca]in) was measured in acutely isolated neurons, using fura-2 microfluorometry. Caffeine caused a substantial increase in [Ca]in following or during high K+ depolarization; this response was inhibited by treatment of the cells with thapsigargin or with caffeine plus ryanodine. The peak value and the rate of the depolarization-induced [Ca]in increase were not much altered by either of these treatments, which deplete caffeine-sensitive Ca2+ stores. The muscarinic receptor agonists muscarine, oxotremorine M, and methacholine, caused substantial increases in [Ca]in, in a manner that was partially dependent on Ca2+. These agonists also caused a rise in [Ca]in during K+ depolarization, which rise was inhibited by treatment with thapsigargin or with caffeine plus ryanodine. The response to oxotremorine M during depolarization was strongly inhibited by 10 nM 4-DAMP, but was not inhibited by 1 microM pirenzepine or by 1 microM AF-DX 116. These results indicate that chick ciliary ganglion cells possess Ca2+ stores that are activated by both caffeine and a second messenger generated by the activation of the M3 muscarinic receptor subtype.

Kudoa intestinalis n. sp. (Myxosporea: Multivalvulida) from the intestinal musculature of the striped mullet, Mugil cephalus, from Japan

Kudoa intestinalis n. sp. (Myxosporea: Multivalvulida) is described from the intestinal musculature of the striped mullet, Mugil cephalus, from the southeastern coast of the Kii Peninsula, Japan. The plasmodia of the new species are spherical or ellipsoidal and contain quadrangular spores that, on the average, measure 3.4 microns in length, 6.5 microns in width and 6.1 microns in thickness. The species is characterized by the presence of short projections at the apex and concave values posteriorly.

Calcium permeability of non-N-methyl-D-aspartate receptor channels in immature cerebellar Purkinje cells: studies using fura-2 microfluorometry

Using fura-2 microfluorometry, I investigated the mechanism by which non-N-methyl-D-aspartate (NMDA) receptor agonists increase the cytosolic free calcium concentration ([Ca]in) in single cerebellar Purkinje cells isolated from 3-10-day-old rats. Kainate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate dose-dependently increased the cytosolic free Na+ concentration, which was measured using sodium-binding benzofuran isophthalate microfluorometry, confirming the Na+ influx through ion channels linked to non-NMDA receptors. The [Ca2+] increases induced by relatively lower concentrations of agonists were entirely dependent on external Ca2+ and were reduced by removal of external Na+ or by addition of a Ca2+ channel blocker, D600. The results indicate that the non-NMDA agonist-induced [Ca]in increase was due mainly to Ca2+ influx through voltage-dependent Ca2+ channels, which were activated by a massive Na+ influx. On the other hand, higher concentrations of agonists dose-dependently increased [Ca]in under conditions in which activation of voltage-dependent Ca2+ channels were blocked by a combination of Na+ removal with D600. These [Ca]in increases were Ca2+ dependent and little affected by adding a competitive NMDA antagonist. Non-NMDA agonists also stimulated influxes of Mn2+ and Co2+, both of which can be monitored by quenching fura-2 fluorescence under the same conditions. These results suggest that ion channels linked to non-NMDA receptors on immature Purkinje cells are permeable to Ca2+, Mn2+, and Co2+.

Possible regulation of caffeine-induced intracellular Ca2+ mobilization by intracellular free Na+

To gain some understanding of the regulatory mechanism involved in caffeine-induced Ca2+ release in adrenal chromaffin cells, we took advantage of the paradoxical observation that removal of divalent cations potentiated the secretory response to caffeine. We measured the concentration of cytosolic free Ca2+ ([Ca]in) in isolated cat chromaffin cells, by fura-2 microfluorometry, to see whether there was any correlation between the secretory response and the rise in [Ca]in. The caffeine-induced [Ca]in rise and catecholamine secretion were increased by treatment of cells with a divalent cation-deficient solution. These potentiated responses were strongly inhibited either by pretreatment with ryanodine, by the reduction of the external Na+ concentration, or by the addition of Ca2+ channel blockers. Removal of divalent cations caused a large rise in the cytosolic free Na+ concentration ([Na]in), which was measured using SBFI microfluorometry. This rise in [Na]in was reduced either by adding Ca2+ channel blockers or by reducing the external Na+ concentration. These results show a good correlation between caffeine-induced Ca2+ release and [Na]in at the time of stimulation, suggesting that caffeine-induced Ca2+ release is regulated by [Na]in.

Possible role of surface potential in the gating mechanism of Ca2+ channels in cat adrenal chromaffin cells: studies with fura-2 microfluorometry

The cytosolic free Ca2+ concentration ([Ca]in) in isolated cat chromaffin cells was measured by fura-2 microfluorometry. During 30 mM KCl depolarization or sucrose substitution for NaCl, a reduction in external Ca2+ concentration under optimal conditions paradoxically caused a rise in [Ca]in and, in separate experiments, in catecholamine secretion. The results support a previously suggested role of surface potentials in the gating mechanism of Ca2+ channels.

A muscarinic receptor agonist mobilizes Ca2+ from caffeine and inositol-1,4,5-trisphosphate-sensitive Ca2+ stores in cat adrenal chromaffin cells

To gain some understanding of the characteristics of intracellular Ca2+ stores of cat adrenal chromaffin cells, we investigated the effects of ryanodine, a blocker of Ca(2+)-induced Ca2+ release channels in muscle, on both cytosolic Ca2+ concentration and catecholamine secretion induced by caffeine or methacholine. The results suggest that Ca2+ stores consist of at least two compartments, one which is sensitive to both caffeine and inositol-1,4,5-trisphosphate (IP3), and the other which is sensitive to IP3 alone.

Internal Ca2+ mobilization by muscarinic stimulation increases secretion from adrenal chromaffin cells only in the presence of Ca2+ influx

The cytosolic free Ca2+ concentration ([Ca2+]in) in single cat and bovine adrenal chromaffin cells was measured to determine whether or not there was any correlation between the [Ca2+]in and the catecholamine (CA) secretion caused by muscarinic receptor stimulation. In cat chromaffin cells, methacholine (MCh), a muscarinic agonist, raised [Ca2+]in by activating both Ca2+ influx and intracellular Ca2+ mobilization with an accompanying CA secretion. In bovine cells, MCh elevated [Ca2+]in by mobilizing intracellular Ca2+ but did not cause CA secretion. The MCh-induced rise in [Ca2+]in in cat cells was much higher than that in bovine cells, but when Ca2+ influx was blocked, the rise was reduced, with a concomitant loss of secretion, to a level comparable to that in bovine cells. Intracellular Ca2+ mobilization due to muscarinic stimulation substantially increased secretion from depolarized bovine and cat cells, where a [Ca2+]in elevated above basal values was maintained by a continuous Ca2+ influx. These results show that Ca2+ released from internal stores is not effective in triggering secretion unless Ca2+ continues to enter across the plasma membrane, a conclusion suggesting that secretion depends on [Ca2+]in in a particular region of the cell.

N-methyl-D-aspartate and aspartate raise the cytosolic free calcium concentration by acting upon receptors transiently expressed on immature cerebellar Purkinje cells

N-Methyl-D-aspartate (NMDA) or aspartate (Asp) increased the cytosolic free calcium concentration ([Ca]in) in some populations of Purkinje cells dissociated from immature rat cerebellum. The NMDA- and Asp-induced rise in [Ca]in was affected only a little by adding glycine or NMDA antagonists, but was reduced either by adding Mg2+, Gallopamil hydrochloride (D-600) and gamma-amino-butyric acid, or by removing external Na+. The results suggest that stimulation of the NMDA-sensitive receptors transiently expressed on immature Purkinje cell soma results in a rise in [Ca]in through the activation of voltage-dependent Ca2+ channels.

Receptor types mediating the rise in the cytosolic free calcium concentration by L-aspartate and L-glutamate in immature cerebellar neurons with N-methyl-D-aspartate receptors

L-Aspartate (Asp) and L-glutamate (Glu) increased the cytosolic free calcium concentration ([Ca]in) in medium-sized cerebellar neurons having N-methyl-D-aspartate (NMDA) receptors. The sustained rise in [Ca]in induced by Asp, but not by Glu, was reduced by the addition of NMDA antagonists, which consistently suppressed the rise in [Ca]in induced by a low concentration of Asp or Glu in combination with glycine. The results suggest that Asp is a more preferential agonist of NMDA receptors than Glu, although Glu can also be an agonist in the presence of glycine.

GABA inhibits the rise in cytosolic free calcium concentration in depolarized immature cerebellar Purkinje cells

gamma-Aminobutyric acid (GABA) reduced the peak rise or slowed the rate of rise in cytosolic free calcium concentration ([Ca]in) induced by quisqualate, kainate, or high KCl in immature cerebellar Purkinje cell bodies. The sustained rise or repeated transient of [Ca]in induced by tetraethylammonium, veratridine, or Bay-K-8644 was lowered to the basal level by adding GABA, although the inhibition by GABA of Bay-K-8644-induced rise in [Ca]in was only slight and transient in some cells. These findings indicate that GABA inhibits the rise in [Ca]in by hyperpolarizing the membrane potentials at Purkinje cell bodies.

Regulation of the cytosolic free calcium concentration by Na+ spikes in immature cerebellar neurons with N-methyl-D-aspartate receptors

N-Methyl-D-aspartate and glycine increased the cytosolic free calcium concentration ([Ca]in) in medium-sized cerebellar neurons. Spontaneous changes in [Ca]in were occasionally observed in NMDA-responsive cells, but large increases in [Ca]in were triggered only through depolarizations by adding veratridine or K+ channel blockers in every cell examined. The [Ca]in increase was suppressed by voltage-dependent Na+ and Ca2+ channel blockers and by an inhibitory transmitter (GABA), suggesting that the generation of Na+ spikes is involved in the increase in [Ca]in.

Possible regulation of the cytosolic-free calcium concentration by Na+ spikes in immature cerebellar Purkinje cells

Isolated immature cerebellar Purkinje cell bodies often exhibit the spontaneous fluctuations of a cytosolic free Ca concentration ([ Ca]in), which was measured by fura-2 microfluorimetry. In silent cells, however, the increase of [Ca]in could be triggered by pharmacological depolarizations (adding veratridine or tetraethylammonium). In any case, these [Ca]in changes were sensitive to voltage-dependent channel blockers (tetrodotoxin and Ca channel blockers) and to an inhibitory transmitter (GABA). The results suggest that the spontaneous activation of voltage-dependent Na+ and Ca2+ channels might be involved in the increase of [Ca]in.

Tetraethylammonium stimulates adrenomedullary secretion by causing fluctuations in a cytosolic free Ca concentration

Tetraethylammonium (TEA) caused marked fluctuations in a cytosolic free Ca concentration, which was measured by fura-2 microfluorimetry in bovine adrenal chromaffin cells. At the same time. TEA stimulated catecholamine secretion from cat and bovine chromaffin cells. Present results suggest that TEA indirectly increases the Ca2+ influx by depolarizing the cell membrane and consequently stimulates catecholamine secretion.

Prolonged exposure to a K-rich medium makes the rat mast cell membrane permeable to external calcium ions

Rat mast cells, pretreated with a Ca-free, high KCl medium for more than 30 min, released histamine when subsequently exposed to a medium containing 0.1-2 mM Ca, despite the absence of voltage-dependent Ca channels. Morphological studies showed that high KCl-treated cells became swollen and that the addition of Ca caused degranulation (exocytosis). Ca-stimulated histamine release was inhibited when the high KCl treatment medium contained dinitrophenol and 2-deoxyglucose. The response to Ca was also observed when KCl in the treatment medium was replaced by RbCl, CsCl, KBr or KNO3. When the high K-treated cells were incubated with 0.5 mM 45Ca at 0-1 degree C, 45Ca uptake by these cells was much larger than that by untreated cells, suggesting that the membrane permeability to Ca of these cells is increased. Although prolonged (90 min) incubation of the cells with an isotonic KCl medium increased the rate of leakage of lactate dehydrogenase possibly reflecting extensive cell swelling, most cells recovered the ability of responding to stimulation with compound 48/80 or with simultaneous removal of Na and Ca when subsequently incubated with a Na-based medium containing Ca. Raising the KCl concentration above normal osmolarity in the treatment medium reduced the extents of cell swelling, without reducing the response to Ca addition. Under various other experimental conditions, a poor correlation was also found between the extents of swelling and the magnitude of the response to Ca. These results raised the possibility that intracellular accumulation of a particular species of anions increased membrane permeability to Ca.

Potentiation by Bay-K-8644 of the adrenal catecholamine secretory response to Ca re-introduction and ouabain: possible activation of Ca influx linked with Na efflux

Catecholamine (CA) secretion induced by Ca re-introduction or ouabain in the presence of Ca is markedly potentiated by Bay-K-8644 in the perfused cat adrenal. The mechanism of potentiation by this Ca agonist was investigated using perfused cat adrenal and isolated bovine chromaffin cells. The stimulatory effect of Bay-K-8644 on the response to Ca was very slight when cat adrenal was perfused with a Ca-deficient medium, in which 1 mM Mg was added or the concentration of Na was lowered. The inhibitory effect of Mg was reversed by inhibition of the Na pump with K deprivation, ouabain, or KCN. The secretion induced by ouabain during maintained depolarization at a lowered concentration (0.25 mM) of Ca, which is supposed to be due to Ca influx in exchange for Na efflux, was larger in the Bay-K-8644 treated adrenal than that in the untreated adrenal. The increase in secretion by the delayed addition of Bay-K-8644 during perfusion with a high K medium containing ouabain was larger when the concentration of Na in a high K medium was higher. When isolated chromaffin cells were stimulated with a Na-free (Tris) medium containing 0.5 mM Ca, CA secretion from and 45Ca uptake into the cells preincubated with a divalent cation-free medium were potentiated by Bay-K-8644. The stimulatory effect of Bay-K-8644 was not seen when a Ca-free treatment medium contained Mg or lacked Na, but the inhibitory effect of Mg was reversed by the addition of ouabain or KCN to the pretreatment medium. When isolated cells preloaded with 45Ca were superfused with a Ca-free medium, Ca re-introduction increased the rate of Ca efflux only under conditions in which significant increases in CA secretion and 45Ca uptake were previously observed under the static incubation system. Bay-K-8644 further increased this Ca efflux rate under these conditions. These results support the view that Ca influx linked with Na efflux is through a pathway with properties similar to those of voltage-dependent Ca channels, and suggest that this Ca pathway is activated by Bay-K-8644, which is an activator of voltage-dependent Ca channels.

Spontaneous and secretagogue-induced changes in cytosolic free Ca concentration measured by microfluorimetry with fura-2 on single bovine adrenal chromaffin cells

The concentration of cytosolic Ca2+ ([Ca]in) was examined in single bovine adrenal chromaffin cells by monitoring fura-2 fluorescence with microspectrofluorimetry. To see the correlation between [Ca]in and secretion, we also measured the rates of catecholamine (CA) secretion and 45Ca efflux from populations of cells. [Ca]in was constant in the majority of single cells, but the small oscillatory changes in [Ca]in were observed in a population of cells. These spontaneous Ca oscillations, when observed, disappeared either after removal of extracellular Ca2+ or by addition of D-600 or Mn2+, but still persisted in the presence of tetrodotoxin (TTX) or after removal of extracellular Na+. In the silent cells the Ca fluctuations were often induced by Bay-K-8644. The characteristics of Bay-K-8644-induced Ca fluctuations were very similar to those of spontaneous ones. Low concentrations of nicotine (1 microM), acetylcholine (ACh; 1-2 microM), or KCl (12.5 mM) often induced oscillations riding on a steady rise in [Ca]in. These changes were rapidly suppressed by removal of either extracellular Ca2+ or Na+, or by addition of either D-600 (methoxyverapamil) or TTX. A low concentration of ACh (1 microM) or KCl (12.5 mM) also increased the rate of 45Ca efflux, but substantial secretion was not detected. On the other hand, the sustained rise in [Ca]in was evoked by 0.1 mM ACh, 20 microM nicotine, or 30 mM KCl, which was suppressed by removal of extracellular Ca2+, but was little affected by TTX. A sustained increase in 45Ca efflux upon exposure to ACh was observed, possibly reflecting the sustained rise in [Ca]in. ACh also stimulated CA secretion, which was faded out during the prolonged application. Veratridine, a Na channel activator, caused repetitive sequence of Ca transients followed by a sustained rise in [Ca]in. These results, together with the previous electrophysiological findings, suggest that: (1) the spontaneous Ca fluctuations are closely associated with occurrence of spontaneous Ca2+ and Na+ action potentials; (2) the rise in [Ca]in induced by a low concentration of nicotinic agonists of KCl is mediated by Na+ action potentials as well as gradual membrane depolarizations; (3) the oscillatory changes subsequent to a rise in [Ca]in reflect fluctuations in Ca2+ influx through the Ca2+ channels; (4) the critical [Ca]in needs to be attained before the CA secretion takes place.

Fluoroaluminates stimulate histamine secretion in the digitonin-permeabilized rat mast cells

The combination of NaF and AlCl3 stimulated histamine secretion from digitonin-permeabilized rat mast cells only in the presence of trace amount of Ca2+. When NaF plus AlCl3 were added together with a maximal dose of guanosine-5'-[gamma-thio]triphosphate (GTP gamma S), the combined effect was less than additive. The results suggest that the secretory effect of fluoroaluminates is, at least partially, mediated by GTP-binding protein, which is previously found to be activated by GTP gamma S.

Capsaicin-induced corneal lesions in mice and the effects of chemical sympathectomy

Effects of chemical sympathectomy on corneal changes induced in mice by a s.c. injection of capsaicin were investigated. Pretreatment with a s.c. injection of 6-hydroxydopamine (6-OHDA) on the 1st and 2nd postnatal day or on the 14th and 15th postnatal day led to a marked suppression of the capsaicin-induced corneal lesions. This suppressive effect also was evident in case of administration after capsaicin treatment. Intraventricular injection of 6-OHDA had a slight, transient effect. DSP4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine], another potent substance used for sympathetic denervation, had a suppressive effect similar to that of 6-OHDA. The concentration of capsaicin in tissues of the head was unaltered with 6-OHDA. The content of substance P (SP) in the ocular anterior segments was decreased, dose-dependently, with capsaicin administration. Neonatal administration of 6-OHDA decreased the rate of capsaicin-induced reduction of SP. However, this effect of 6-OHDA was too slight to explain the suppression of the corneal lesions, as the intensity score of lesions with a large dose of capsaicin after 6-OHDA was lower than that with a small dose of capsaicin without 6-OHDA, whereas SP content in the former was still much lower than that in the latter. On the other hand, the content of norepinephrine in the ocular tissues was decreased in the presence of 6-OHDA but not capsaicin. These results suggest that the corneal changes induced by capsaicin are largely inhibited by a decreased activity in the peripheral sympathetic system.

The secretory mechanism in adrenal chromaffin cells by nitrophenol compounds: possible involvement of the change in the surface potentials

The rabbit adrenal gland was perfused with a modified Locke's medium and the mechanism of adrenaline secretion induced by nitrophenol compound was investigated. The secretory response to 2,4-dinitrophenol (DNP) or trinitrophenol (TNP) showed the following peculiar features. (1) Prolonged exposure to DNP or TNP caused an immediate, and long-lasting increase of secretion only in the presence of Ca. (2) The response to DNP depended on the concentration of Ca, but that to TNP was largest in the presence of 0.5 mM Ca. (3) Re-addition of 2 mM Ca during prolonged exposure to DNP or TNP produced a larger response than did the simultaneous addition of Ca and either DNP or TNP. (4) The response to DNP in the presence of 2 mM Ca was markedly reduced by removal of external Na, but the Na dependency became less marked in the presence of 0.1 mM Ca. The response to TNP in the presence of 0.5 mM Ca was slightly reduced in the absence of Na. (5) DNP or TNP caused a much larger response during depolarization with a high K, Rb, or Cs medium than that with a 5 mM KCl medium. (6) The response to DNP was largely potentiated in the absence of most ions in the presence of only 0.1 mM Ca and that to TNP was potentiated in the presence of only 0.5 mM Ca under the same condition. (7) Re-addition of Ca 5 min after the removal DNP or TNP still caused substantial secretion. These results suggest that nitrophenol compounds stimulate secretion by two independent mechanisms: one is related to its effect on the surface potentials of the plasma membrane and the other unknown except for the possible dependence of Na and Ca.

Possible role of surface potential in the gating mechanism of Ca channels concerned with catecholamine secretion in the adrenal

Cat adrenal gland was perfused retrogradely with modified Locke's medium and we investigated the effect of divalent cations on catecholamine release in response to KCl depolarization and to substitution of sucrose for NaCl in order to study the role of surface potential in the gating mechanism of Ca channels. The response to 20 mM KCl was largest at 10 mM Sr and it was less at 20 and 40 mM. Inhibition by the higher concentration of Sr was weakened by the addition of 10 mM Mg to the medium or by raising the concentration of KCl. The response to 30 mM KCl at 10 mM Sr was much larger than that at 10 mM Ca, and it was reduced by the addition of Ca. Stronger depolarization tended to reduce the difference between Ca and Sr in supporting secretion. The addition of 10 mM Sr increased the response to 30 mM KCl in the presence of 0.1 or 0.5 mM Ca, but tended to reduce the response in the presence of 2 or 10 mM Ca. Response to sucrose substitution was also reduced by increasing the concentration of Ca or Sr. Inhibition by Ca was counteracted by raising the concentration of K, Rb, or Cs so that the concentration of Ca producing the maximum response tended to be higher. Similarly, inhibition by Sr was partially reversed by raising the KCl concentration to 15 mM. These results are in accord with the idea that a high concentration of permeant divalent cations reduces the number of activated Ca channels by decreasing the surface potential, and also that Ca is more effective than Sr in decreasing the surface potential by binding to the surface negative charges. Increase of catecholamine secretion by a novel dihydropyridine BAY K 8644 was greater in the presence of Sr than with Ca.

Mechanism of histamine secretion from rat mast cell by calcium reintroduction

Rat mast cells treated with Ca-free medium were stimulated with Ca reintroduction and its secretory mechanism was investigated. The response was modulated by experimental manipulations which are supposed to alter the level of internal Na, suggesting the involvement of internal Na in this response.

Tumor promoters potentiate the adrenomedullary secretion induced by acetylcholine and excess K possibly by stimulating phorbol ester receptors

Catecholamine secretion from the perfused cat adrenal in response to 15 mM KC1 or acetylcholine was significantly increased by treatment with active tumor promoters. A good correlation was found between potentiation of the secretory response and the phorbol ester receptor binding activity, suggesting that promoters modulate the secretory mechanism via the receptors.

Removal of extracellular Ca stimulates histamine release from rat mast cells by mobilizing a labile cellular source of Ca

Rat mast cells were stimulated by simultaneous removal of external Ca and Na, and their secretory mechanism was investigated. A brief EGTA-treatment of the cells markedly diminished this response with little affection the response to compound 48/80, suggesting that mobilization of Ca from labile pools in the membrane is involved in this response.

Mechanism of calcium efflux from isolated bovine adrenal chromaffin cells

Chromaffin cells isolated from bovine adrenals and maintained in culture were loaded with 45Ca, and the mechanism of 45Ca efflux from these cells was investigated. During exposure to a Ca-deficient, Mg (1 mM)-containing medium, replacement of NaCl with sucrose, choline Cl, or Tris Cl reduced the rate of 45Ca efflux by approx. 30-40%, showing the presence of a Na-dependent 45Ca efflux mechanism. In contrast to the previous findings, however, Li can partially replace Na in maintaining 45Ca efflux. Reintroduction of Ca to a Ca-deficient medium increased the rate of 45Ca efflux depending on the concentrations of Ca, showing the presence of a Ca-dependent Ca efflux mechanism. The marked but transient rise in the rate of 45Ca efflux in response to Ca reintroduction was observed under conditions in which the concentration of internal Na was raised either by inhibiting Na pumping activity (ouabain or K removal) or by removal of Mg from the medium. The increased 45Ca efflux was further potentiated by simultaneous Na removal and was markedly inhibited by Ca channel blockers, suggesting that the transiently increased Ca influx in exchange for internal Na facilitated the rate of 45Ca efflux. However, other conditions which evoke catecholamine secretion by stimulating Ca influx also increased the rate of 45Ca efflux, suggesting that the increased Ca influx via any route increases 45Ca efflux. These results thus confirmed the presence of both Na-dependent and Ca-dependent Ca efflux mechanisms in chromaffin cells.

Operation of internal Na-dependent Ca influx mechanism associated with catecholamine secretion in the adrenal chromaffin cells

The cat adrenal gland was retrogradely perfused with a medium lacking divalent cation, and the secretion of catecholamines was induced by Ca reintroduction with or without simultaneous removal of external Na. These responses were markedly reduced after prior exposure to a medium containing Mg (1 mM) or lacking Na. The inhibition caused by Mg was reversed by ouabain treatment. Reversing the concentration gradient for Na alone by replacing external Na with Tris, choline, or Li did not stimulate catecholamine secretion when Ca2+ (0.1 mM) was present in the external medium throughout the experiment. However, the treatment with ouabain reversed this inhibitory effect of Ca so that Na removal did induce marked secretion. Essentially similar results concerning secretion were obtained in the cultured bovine chromaffin cells. There was a reasonable correlation between secretion and 45Ca uptake in these cells under various experimental manipulations, and alterations of these parameters were well correlated with the level of internal Na. Furthermore, the rate constant of 22Na efflux was found to increase when Ca was reintroduced with the simultaneous removal of Na during exposure to a medium containing ouabain. These results are consistent with the view that the mechanism of internal Na-dependent Ca influx is activated to induce catecholamine secretion whenever internal Na is raised above a critical level. On the other hand, there were significant increases in the catecholamine secretion and 45Ca uptake which were induced by substitution of NaCl with sucrose, even when the operation of the internal Na-dependent Ca influx mechanism was markedly restricted by various experimental manipulations. This suggests that other secretory mechanisms are involved under these conditions. This would account for the largest secretory effect of sucrose substitution under the condition in which internal Na-dependent Ca influx is activated.

Inhibition of Na pumps enhances Ca-dependent release of vasopressin from the isolated neurohypophysis of the rat

The isolated neurohypophysis of the rat was incubated with a medium lacking Ca and vasopressin release was induced by reintroduction of Ca (2 mM). The response to Ca was greatly enhanced after treatment with a medium containing ouabain or lacking K. The enhanced release of vasopressin by ouabain was dependent on the concentration of external Na. The results suggest that inhibition of Na pumps leads to a rise in internal Na, thereby activating Na-dependent Ca influx mechanism associated with vasopressin release.

A small increment of external K concentration accelerates adrenomedullary catecholamine secretion induced by ouabain and metabolic inhibitors

In the cat adrenal perfused with a medium containing ouabain, raising the external concentration of K to 10 mM abruptly increased the rate of catecholamine secretion. Increased response to 10 mM K were also observed in the adrenals treated with monoiodoacetate or cyanide, which was suggested to reduce the Na pumping activity indirectly. Since both the onset time and the magnitude of K-induced secretion are dependent on the concentration of external Na, it was suggested that a small increase of K concentration accelerates Ca influx in exchange for internal Na.