Catecholamine release from bovine adrenal medulla in response to maintained depolarization.Journal of Physiology 253:593-620

The Journal of Physiology (Impact Factor: 5.04). 01/1976; 253(2):593-620. DOI: 10.1113/jphysiol.1975.sp011209
Source: PubMed


Prolonged exposure of venous-perfused bovine adrenal glands to high K in the presence of external Ca produces a transient increase in catecholamine output that reaches a maximum after about 1 min and then declines with a half-time of about 1-2 min. 2. The time course of the transient secretory response to high K does not depend appreciably on the total catecholamine output which indicates that depletion of releasable catecholamine is unlikely to be responsible for the transient nature of the response. 3. Application of 3-6 mM-Ba stimulates secretion from a gland after many minutes exposure to high K, when catecholamine output has declined close to resting levels. This provides further evidence that depletion does not play a major role in the transient response and shows that maintained depolarization does not inhibit the secretory mechanism. 4. Exposure to high K solutions in which Ca has been replaced isomotically by Mg does not evoke any catecholamine output. Subsequent application of Ca always elicits some secretion although the size of this response to added Ca declines rapidly during exposure to Ca-free, high K solutions. The failure of the secretory response in these experiments is more rapid, and earlier in onset than the declining phase of the normal secretory response evoked in the presence of calcium. 5. Pre-treatment with Ca-free solutions of intermediate K content reduces the response to subsequent simultaneous application of high K and Ca. There is a roughly sigmoidal relation between the reduction in response and the logarithm of the K concentration used for pre-treatment. 6. Thin slices of bovine adrenal medulla show qualitatively similar responses on exposure to high K. Examination of the flourescent signal from slices dyed with the potential-sensitive dye DiS-C(3)-(5) suggests that maintained exposure to high K produces a stable depolarization. 7. The most likely explanation for these results is that K-depolarization first activates and subsequently inactivates a potential-sensitive Ca permeability channel. This inactivation is time and possibly potential dependent. 8. The effect of high K on calcium movements in medullary slices was examined. Exposure to 72 mM-K increases (45)Ca uptake, the increase being greatest during the first 10 min. The efflux of Ca is also increased on exposure to high K in the presence of Ca. The net Ca uptake in 72 mM-K is smaller than the tracer uptake of Ca. These findings indicate that K depolarization stimulates a Ca-Ca exchange process. They are also consistent with, but do not offer strong positive support for, the idea that K-depolarization first activates and subsequently inactivates Ca entry. 9. It is suggested that Ca inactivation might play a role in the modulation of neurosecretion and neurotransmitter release by changes in membrane potential.

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    • "Chroman cells secrete CA in response to di€erent stimuli including exposure to nicotinic agonists (Holz & Senter, 1981; Schneider et al., 1981) and passive membrane depolarization by increasing concentrations of extracellular K + (Ishikawa & Kanno, 1978; Baker & Rink, 1975). Following membrane depolarization, voltage-dependent Ca 2+ channels located in the plasma membrane open (Fenwick et al., 1982; CenÄ a et al., 1989) producing an increase in intracellular Ca 2+ concentration ([Ca 2+ ] i ) (Kao & Schneider, 1986; Calvo et al., 1995). "
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    ABSTRACT: The molecular mechanisms involved in veratridine-induced chromaffin cell death have been explored. We have found that exposure to veratridine (30 μM, 1 h) produces a delayed cellular death that reaches 55% of the cells 24 h after veratridine exposure. This death has the features of apoptosis as DNA fragmentation can be observed. Calcium ions play an important role in veratridine-induced chromaffin cell death because the cell permeant Ca2+ chelator BAPTA-AM and extracellular Ca2+ removal completely prevented veratridine-induced toxicity. Following veratridine treatment, there is a decrease in mitochondrial function and an increase in superoxide anion production. Veratridine-induced increase in superoxide production was blocked by tetrodotoxin (TTX; 10 μM), extracellular Ca2+ removal and the mitochondrial permeability transition pore blocker cyclosporine A (10 μM). Veratridine-induced death was prevented by different antioxidant treatments including catalase (100 IU ml−1), N-acetyl cysteine (100 μM), allopurinol (100 μM) or vitamin E (50 μM). Veratridine-induced DNA fragmentation was prevented by TTX (10 μM). Veratridine produced a time-dependent increase in caspase activity that was prevented by Ca2+ removal and TTX (10 μM). In addition, calpain and caspases inhibitors partially prevented veratridine-induced death. These results indicate that chromaffin cells share with neurons the molecular machinery involved in apoptotic death and might be considered a good model to study neuronal death during neurodegeneration. British Journal of Pharmacology (2000) 130, 1496–1504; doi:10.1038/sj.bjp.0703451
    Full-text · Article · Sep 2000 · British Journal of Pharmacology
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    • "We have utilized methodological approaches which allow evoked changes in [Ca2+]i, measured in single isolated nerve endings, to be correlated to AVP secretion on a time resolved scale of seconds. We have observed, consistent with observations on other secretory systems (Baker & Rink, 1975; Llinas & Nicholson, 1975; Miledi & Parker, 1981; Cheek, Jackson, O'Sullivan, Moreton, Berridge & Burgoyne, 1989), that a decline in AVP secretion occurs despite a sustained increase in [Ca2+]i in both intact and permeabilized neurohypophysial nerve endings. However, our results suggest that, in the neurohypophysis, the decline in AVP secretion cannot be explained solely on the basis of a decline in Ca2+ conductance of the nerve ending coupled with inadequate spatiotemporal resolution of Ca2+ dynamics, or depletion of an immediately releasable store of granules or different sensitivities of Ca2+ receptors. "
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    ABSTRACT: 1. Monitoring of [Ca2+]i and vasopressin secretion in isolated nerve endings from the rat neurohypophysis were studied to determine the relationship between the time course of vasopressin secretion and depolarization-induced changes in [Ca2+]i. 2. Membrane depolarization by increasing the extracellular [K+] led to concentration-dependent, parallel increases in the amount of vasopressin release and in peak increases in [Ca2+]i. Half-maximal activation of a change in [Ca2+]i was attained at 40 mM extracellular K+. 3. The Ca2+ chelator dimethyl-BAPTA (1,2-bis(O-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid), loaded into the nerve endings, reduced K+ depolarization-evoked vasopressin release and efficiently antagonized K(+)-induced changes in [Ca2+]i. Moreover, dimethyl-BAPTA dramatically reduced basal [Ca2+]i without a reduction in basal secretion. 4. The duration of the vasopressin secretory response was similar regardless of applied 50 mM K+ depolarizations longer than 30 s. The t1/2 of the secretory response was 45 s. Application of repetitive K+ depolarization pulses repetitive secretory responses of similar amplitude and duration. 5. The K(+)-induced changes in [Ca2+]i remained elevated throughout the duration of the depolarizing stimulus decreasing less than 30% over 3 min. The sustained increase in [Ca2+]i resulted largely from continued enhanced Ca2+ influx, demonstrated by susceptibility to the dihydropyridine, L-type calcium channel blocker, nicardipine. 6. Vasopressin secretion could be reinitiated following its decline to a step K+ depolarization by a further step increase in K+ or by removal and readdition of extracellular [Ca2+]. Alterations in [Ca2+]i paralleled periods of secretory activity. 7. Analysis of secretory responsiveness and change in [Ca2+]i to K+ depolarization in medium of altered extracellular [Ca2+] indicates that [Ca2+]i of 20 microM is sufficient to trigger vasopressin release. K(+)-induced alterations in [Ca2+]i could be observed at [Ca2+]o as low as 5 microM. Although smaller in amplitude to that observed at 2.2 mM [Ca2+]o the duration of the K(+)-induced secretory response increased at lower [Ca2+]o. 8. Transient vasopressin secretory responses were observed to sustained levels of [Ca2+] in digitonin and streptolysin-O-permeabilized nerve endings. Secretion could be re-evoked, following its decline, by a step increase in [Ca2+] or by removal and readdition of [Ca2+]o.(ABSTRACT TRUNCATED AT 400 WORDS)
    Preview · Article · Sep 1993 · The Journal of Physiology
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    • "For the sake of clarity, we will call depolarization that period preceding any Ca2+ pulse to challenge the adrenal medullary chromaffin cells to secrete catecholamines. It has been demonstrated that in rat (Ishikawa & Kanno, 1978) and ox adrenal glands (Baker & Rink, 1975), high K+ concentrations cause a sustained depolarization of their chromaffin cells. "
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    ABSTRACT: 1. Inactivation by voltage changes of 45Ca2+ uptake into and catecholamine release from cat adrenal glands perfused at a high rate (4 ml/min) at 37 degrees C with oxygenated Krebs-Tris solution has been studied. Experimental conditions were selected so that adrenal medullary chromaffin cells were depolarized for different time periods and with various K+ concentrations in the absence of Ca2+, prior to the application of 0.5 mM-Ca2+ for 10 s in the presence of 118 mM-K+ to test the rate of secretion (the 'Ca2+ pulse'). 2. Application of the Ca2+ pulse after perfusion with 5.9 mM-K+ led to a 100-fold increase of the basal rate of secretion. However, if the Ca2+ pulse was preceded by a 10 min period of perfusion with 118 mM-K+, the secretory response was decreased by over 80%. 3. Inactivation of secretion starts 10-30 s after high-K+ perfusion and is completed 2-5 min thereafter. Inactivation is readily reversed by perfusing the glands with normal K(+)-containing solution; the recovery phenomenon is also gradual and time-dependent, starting 30 s after repolarization and ending 300 s thereafter. 4. The rate of inactivation is much slower at 35 than at 118 mM-K+, suggesting that the process is strongly dependent on voltage. 5. Like catecholamine release, Ca2+ uptake into adrenal medullary chromaffin cells is inactivated in a voltage-dependent manner. This, together with the fact that Cd2+ blocked secretion completely and inactivation was seen equally using Ca2+ or Ba2+ as secretagogues, suggests that inactivation of a certain class of voltage-dependent Ca2+ channels is responsible for the blockade of secretion. Such channels must be slowly inactivated by voltage and highly sensitive to dihydropyridines, since (+)PN200-110 (an L-type Ca2+ channel blocker) enhanced the rate of inactivation and (+/-)Bay K 8644 (an L-type Ca2+ channel activator) prevented it, indicating that they might belong to L-subtype Ca2+ channels. 6. The effects of (+/-)Bay K 8644 (100 nM) were seen on both the voltage and time dependence of inactivation. At a moderate depolarization (35 mM-K+), the drug prevented inactivation and caused potentiation of secretion which developed gradually; at strong depolarizations (118 mM-K+), Bay K 8644 prevented the time-dependent development of inactivation. (+)PN200-110 (30 nM) did not suddenly decrease catecholamine release at the earlier times of depolarization; what the drug did was to accelerate the normal rate of inactivation induced by depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
    Full-text · Article · Oct 1990 · The Journal of Physiology
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