Effect of glucagon on digestive enzyme synthesis, transport and secretion in mouse pancreatic acinar cells.

Abstract

SUMMARY1. Effect of glucagon on amylase secretion and lactic dehydrogenase (LDH) release from functionally intact dissociated pancreatic acinar cells and acini was studied.2. In dissociated rat pancreatic acinar cells, the rate of amylase secretion was increased by 70 % with bethanechol (maximally effective concentration, 10-4 M) and 125 % with A23187 (10-5 M), but the response to cholecystokinin-pancreozymin (CCK-PZ) was inconsistent. In dissociated cells from mouse pancreas, the increases amounted to 78 % with bethanechol (10-4 M), 134 % with A23187 (10-5 M) and 82 % with CCK-PZ (maximally effective concentration, 0 01 u. ml.-'). Glucagon in concentrations ranging from 10-7 to 10-4 M increased amylase secretion by 3, 26, 67 and 80 %, whereas secretin (10-8-10-5 M) increased amylase secretion by 8, 39, 88 and 138 %. LDH release was increased with A23187 in concentrations greater than 10-6 M.3. CCK-PZ, bethanechol and A23187 used in maximal concentrations potentiated the effect of a submaximal dose of glucagon whereas secretin did not have an additive or a potentiating effect.4. Pancreatic acini were 3 times more responsive to secretagogues than cells.The dose-response curves to bethanechol, glucagon and CCK-PZ for increase in amylase secretion were similar. LDH release was not increased by these agents.Cytochalasin B (5 ,g ml.-') which is known to disrupt the integrity of luminal membrane inhibited the amylase secretion stimulated by glucagon, bethanechol and CCK-PZ.5. Glucagon inhibited incorporation of a mixture of fifteen '4C-labelled amino acids (algal profile, Schwarz Mann) into perchloric acid precipitable proteins in dissociated mouse pancreatic acini within 30 min. 6. In 'pulse-chase' experiments, glucagon decreased the specific activity of zymogen granules isolated by differential centrifugation, from pancreatic lobules (120 min) and increased the specific activity of radiolabelled proteins in the medium (60 and 120 min).7. It is concluded that glucagon increased digestive enzyme secretion from pancreatic acinar cells by a direct action (in contrast to its reported indirect effects in vivo) and decreased digestive enzyme synthesis. The data on transport and secretion do not support the suggested role of glucagon as an inhibitor in the intact animal.

Inhibitory influence of amino acids on Secretagogues induced exocrine secretion in isolated perfused rat pancreas.

“…TOKUTAKE et al (1976) suggested that inhibition of amino acids on pancreatic exocrine secretion in dogs may be attributed to the direct action of plasma glucagon increased by amino acids administration. The administration of glucagon in vivo causes a short-term inhibition of pancreatic secretion, and in vitro can act directly on the secretion (NAKAJIMA and MAGEE, 1970;MANABE and STEER, 1979;SINGH, 1980). In the present experiment, the inhibitory response induced by amino acids could not be repeated by using exogenous glucagon and insulin.…”

The islet-acinar axis of the pancreas: more than just insulin

“…Glucagon's effect on exocrine secretion is inconsistent. Early work using extracted glucagon applied to mouse, guinea pig, or rat pancreatic acinar cells reported a stimulatory influence (115,149,178,179). However, subsequent studies using biologically active synthetic glucagon failed to confirm this finding (149).…”

Amylase release from dissociated mouse pancreatic acinar cells stimulated by glucagon: effect of membrane stabilizers.

“…Due to theoretical advantages in studying physiological phenomena in single cells (especially the ability to control the extracellular environment rapidly and predictably and a very small extracellular space so that small fluxes of ions critical for secretion can be detected), investigators have tried to use dissociated pancreatic acinar cells obtained by combined procedures of digestion of tissue by enzymes, mechanical disruption and Ca2+ chelation with EGTA or EDTA (Amsterdam & Jamieson, 1974a;Gardner, Conlon, Klaeveman, Adams & Ondetti, 1975;Williams, Cary & Moffat, 1976;Kondo & Schulz, 1976;Kempen, DePont & Bonting, 1977;Renckens, Schrijen, Swarts, DePont & Bonting, 1978;Case & Clausen (see Case, 1978); Singh, 1978Singh, , 1980b. However, in practice, it has been observed that dissociated cells respond poorly to physiological secretagogues (Kondo & Schulz, 1976), possibly due to damage of cell surface receptors (Case, 1978) and need about a tenfold greater concentration of agonists than intact tissue to elicit enzyme secretion (Amsterdam & Jamieson, 1974b;Williams et at.…”

“…Cell counts showed that more than 95 % of the cells were acinar and were intact by trypan Blue exclusion studies. Characterization of isolated cells, including intracellular ion content and response to secretagogues, is reported elsewhere (Singh, 1980b).…”

“…The digestion medium also contained 0.1 mM-CaCl2, collagenase 0 75 mg ml.-' (Sigma, Type I) and 1-5 mg ml.-' hyaluronidase (Sigma, Type I). Dissociated acinar cells were prepared by modifications of techniques developed by Amsterdam & Jamieson (1974a, b) as described in detail in anearlier publication (Singh, 1980b). Cell counts showed that more than 95 % of the cells were acinar and were intact by trypan Blue exclusion studies.…”