Effect of sodium and calcium on basal secretory activity of rat neurohypophysial peptidergic nerve terminals.

Abstract

SUMMARY1. The release of arginine vasopressin (AVP) from a perifused preparation of peptidergic nerve terminals isolated from rat neurohypophyses was studied during manipulations of the external sodium and calcium concentrations. Intracellular concentrations of these two ions were manipulated by use of ouabain and a calcium ionophore, respectively.2. Removal of extracellular Na+ caused, in a concentration-dependent manner, a significant decrease of secretory activity. Conversely, graded addition of Na+ to a Na+-free perifusion medium increased secretion. Half-maximal activation of secretory activity was attained at ca 75 mm [Na+]O. 5. Ouabain (0O1 mM) increased the basal secretory activity and potentiated the secretory response to removal of Ca2+ from the perifusion medium.6. The Ca2+ ionophore A23187 stimulated, in a concentration-dependent fashion, the secretory activity of the peptidergic nerve terminals and this stimulation was strictly dependent on the presence of Ca2+ in the perifusion medium.7. These results show that basal secretion is directly dependent on [Na+]o and indicate that intracellular Na+ is an important factor in the control of secretory mechanisms. Evidence is presented in regard to a possible antagonistic effect of extracellular Ca2+ and Na+ on secretion.

Intracellular calcium and vasopressin release of rat isolated neurohypophysial nerve endings.

“…The large reduction in evoked AVP release in BAPTA-loaded endings Periods of K+ depolarization indicated by filled bar with durations of 60 s for the first periods, 30 s for the second to fourth periods and 150 s for the last period. B, cumulative AVP release corresponding to data presented in A. loaded nerve endings was not observed (17-7+2±3 pg min-', control versus 19-5 + 1P9 pg min-', BAPTA-loaded; 3 < n < 4) suggesting that basal AVP secretion, under these conditions, may be dependent upon factors in addition to [Ca2+]i (Toescu & Nordmann, 1991). Treatment with dimethyl sulphoxide, used as carrier for BAPTA AM, had no effect on the secretory response (n = 3) or induced changes in ( Fig.…”

Contribution of functional voltage‐gated Na+ channel expression to cell behaviors involved in the metastatic cascade in rat prostate cancer: II. Secretory membrane activity

“…Influx of Na þ could have an effect upon the secretory system without involving a significant change in the intracellular Ca 2þ concentration. Intracellular Na þ has indeed been shown to be an important factor in the control of basal secretion from mammalian neurohypophysial terminals (e.g., Toescu and Nordmann, 1991). In addition, at the frog neuromuscular junction, action potential activity, and to a lesser extent intracellular Ca 2þ , has been shown to determine the time course of endocytosis (Wu and Betz, 1996).…”

Modulation/physiology of calcium channel sub-types in neurosecretory terminals

“…In order to address such questions, we have developed a preparation of isolated neurohypophysial terminals [19,37–40]. Electron microscopy [29] and immunocytochemistry [19,20] have been used to characterize this preparation.…”