Stimulation of calcium‐dependent release of labelled protein from pulse‐labelled mouse pituitary intermediate lobe tissue

Abstract

However, recovery also occurred during maintained depolarization provided the Ca concentration was reduced sufficiently. Recovery was complete at 0 4 mM-Ca or less, and at higher concentrations the extent of recovery depended on the Ca concentration selected.6. It is concluded that depolarization opened potential-dependent Ca channels.permitting Ca entry and causing the release of labelled products. The response was brief probably because the Ca channels were inactivated. Since the channels were not inactivated by depolarization in low Ca, inactivation may result from Ca entry.

Secretion of Pro-Opiocortin Peptides from Isolated Perfused Rat Pars intermedia Cells

“…In agreement with the results of others [56,61], depolari zation by a solution containing 45 itiMK* ions caused the simultaneous parallel stimulation of POC-reiated peptides from isolated PI cells. This contrasts with the inhibitory ef fect of high K+ ion concentration on the secretion of a-MSH and (5-endorphin from rat NILs [46, 57,63], which was shown to be due to the indirect effect of DA released from depolarised dopaminergic nerve terminals in this tissue [58].…”

“…This contrasts with the inhibitory ef fect of high K+ ion concentration on the secretion of a-MSH and (5-endorphin from rat NILs [46, 57,63], which was shown to be due to the indirect effect of DA released from depolarised dopaminergic nerve terminals in this tissue [58]. The K*-induced stimulation of POC-related peptides from perfused PI cells was abolished reversibly in the absence of Ca~ ions and mirrored numerous reports of the Ca~ depen dence of high K+-stimulated release from the PI [5,46,56,61,62]. The dramatic stimulatory response of the PI cells which occurred after the first exposure of the cells to a high K+ ion concentration in the absence of Ca~ ions ( fig.…”

Effects of BAY K 8644 and Other Dihydropyridines on Basal and Potassium-Evoked Output of MSH from Mouse Melanotrophs in vitro

“…Evidence for such channels in rat melanotrophs has been obtained by intracel-lular recordings which demonstrate action potentials with a Ca component blockable by Co2+ [7], In contrast to many other endocrine cells, however, including most other adenohypophyseal cells, the melanotrophs show a relatively high basal secretory activity in vitro. There is evidence that this basal secretion may also involve Ca influx since it too is inhibited by Ca lack or addition of Co2+ [31,34]. However the nature of this presumed Ca influx is unclear.…”

“…The melanotrophs may be stimulated to secrete by manipulations demonstrated to de polarize these cells [8,30] such as excess K+ [16, 31, 34] or veratridine [35]. Furthermore, secretion evoked by such de polarizing stimuli is suppressed by a brief omission of Ca2+ or addition of Co2+ [31,34], which blocks Ca channels [ 12]. In these respects melanotrophs behave like chromaffin cells and many other endocrine cells in which secretion can be evoked by opening voltage-regulated Ca channels thereby permitting Ca2+ to enter the cell [4,5].…”

“…21]. The melanotrophs may be stimulated to secrete by manipulations demonstrated to de polarize these cells [8,30] such as excess K+ [16,31,34] or veratridine [35]. Furthermore, secretion evoked by such de polarizing stimuli is suppressed by a brief omission of Ca2+ or addition of Co2+ [31,34], which blocks Ca channels [ 12].…”