The effect of extracellular calcium deprivation on amylase secretion and ⁴⁵Ca efflux from rat pancreas

Abstract

SUMMARY1. The role of extracellular Ca2+ in pancreatic enzyme secretion and 45Ca efflux evoked by acetylcholine (ACh) and caerulein has been assessed in the incubated, uncinate pancreas of young rats.2. In a medium containing 2-5 x 10-3 M-Ca2+, the maximal rates of amylase secretion evoked by optimal doses of each secretagogue were similar. However, the time courses of amylase release during prolonged stimulation of the gland were different.3. The time course of amylase secretion in response to an optimal dose of ACh (10-5 M) was characterized by an initial rapid increase followed by a slow sustained rise. For caerulein (10-8 M), an initial rapid rise was followed either by a plateau or slight decline in the rate of amylase secretion.4. Both secretagogues produced similar increases in the rate coefficient of 45Ca efflux from the gland.5. With supra-optimal doses of the secretagogues, amylase secretion, but not the rate coefficient of 45Ca efflux, was depressed.6. Reducing the extracellular Ca2+ concentration did not have a marked effect on basal amylase secretion but inhibited the action of both secretagogues. When the Ca2+ concentration was 10-6 M or lower, these inhibitory effects were irreversible. Amylase secretion stimulated by ACh was more sensitive to extracellular Ca2+ deprivation than that stimulated by caerulein, the concentration required for half-maximal secretion being about 9-fold greater for ACh.7. Decreasing the extracellular Ca2+ concentration increased both the basal and stimulated rate coefficients of 45Ca efflux.8. Our results support the hypothesis that pancreatic enzyme secretagogues act by releasing bound Ca2+ from sites within the acinar cell. Furthermore, they suggest that the site utilized by ACh is more amenable to depletion, via changes in extracellular Ca2+ concentration, than that employed by caerulein. * Reprints should be requested from R. M. Case, whose present address is: Department of Physiology, Stopford Building, University of Manchester, Manchester M13 9PT.

Mechanism of action of magnesium on acetylcholine‐evoked secretory responses in isolated rat pancreas

“…Other workers have shown that the initial Ca 2+ rise in stimulated acini is attributed to a release of Ca2+ from intracellular stores Ansah et al 1986). During secretion there is an increase in net extracellular Ca2+ taken up (Williams, 1980;Argent, Case & Hirst, 1982;Case, 1984;Putney, 1986). If Mg2+ were competing with Ca2+ at extracellular sites of Ca21 uptake it would not be expected that the initial rise of [Ca2+], from intracellular stores, would be affected.…”

“…Other workers have shown that the initial Ca 2+ rise in stimulated acini is attributed to a release of Ca2+ from intracellular stores Ansah et al 1986). During secretion there is an increase in net extracellular Ca2+ taken up (Williams, 1980;Argent, Case & Hirst, 1982;Case, 1984;Putney, 1986 One such enzyme is the Mg2"-dependent Ca2+-ATPase which is located at the plasma membrane and actively extrudes intracellular Ca2+ against an inwardly directed electrochemical gradient (Lambert & Christophe, 1978;Williams, 1980;Putney, 1988). This enzyme should increase Ca2" extrusion in the presence of high Mg2" levels.…”

The effects of manganese, cobalt and calcium on amylase secretion and calcium homeostasis in rat pancreas

“…All physiological experiments were carried out using the isolated, uncinate portion of the young rat pancreas (Case & Clausen, 1973). Most experiments involved the simultaneous measurement of 45Ca efflux and amylase secretion, details of which are given in the preceding paper (Argent et al 1981). The standard incubation medium was a Krebs-Ringer bicarbonate buffer of the following composition: 12 x 10-1 M-NaCl, 4 5 x 103 M-KCl, 2-5 x 103 M-CaCl2, 103 MMgSO4, 103 M-NaH2PO4, 2-5 x 102 M-NaHCO3, 5-0 x 10-3 M-D-glucose and 0 1 % dialysed bovine serum albumin.…”

Mechanism of action of extracellular calcium on isoprenaline‐evoked amylase secretion from isolated rat parotid glands.

“…Finally, we have also been able to show that the activity of parotid adenylate cyclase can be modulated by Ca2+ over the concentration range thought to prevail inside cells. A preliminary account of some of these observations has already been published (Argent & Arkle, 1983). METHODS Animals and tissue preparation.…”

“…4'Ca efflux and amylase secretion were measured as described by Argent et al (1982). After loading for 60 min in standard incubation medium containing 45CaC12 (2 sCi/ml), the glands were washed for up to 160 min by transfer through a series of vials containing non-radioactive KRBB.…”