Calcium Metabolism and Enzyme Secretion in Guinea Pig Pancreas

Publisher Website
Google Scholar
Abstract
In isolated pancreatic acinar cells from the guinea pig stimulation of enzyme secretion by carbamoylcholine is slightly diminished in the absence of extracellular Ca. LaCl3in a concentration, which does not influence the secretory response to carbamoylcholine, nearly completely abolishes45Ca uptake by cells, indicating that Ca uptake is not necessary for secretion.In cells preloaded with45CaCl2, addition of carbamoylcholine leads to an immediate release of45Ca, Which can be blocked by atropine or 8‐(N,N‐diethylamino)‐octyl 3,4,5‐trimethoxybenzoate and is not influenced by LaCl3in concentrations, which do not inhibit secretion.A similar release of45CaCl2from preloaded cells is obtained by addition of the mitochondrial inhibitors antimycin A, carbonylcyanideptrifluoromethoxyphenylhydrazone (FCCP), and oligomycin. Possibly due to markedly diminished ATP levels, neither antimycin A nor FCCP act as secretagogues, both compounds being inhibitors of secretion. Oligomycin, which decreases ATP levels only to 20%, stimulates secretion.Mitochondria and microsomes from pancreatic tissue are able to accumulate45Ca. Mitochondrial45Ca uptake can be driven by ATP or active respiration and is inhibited by NaN3, oligomycin, antimycin A or FCCP. Microsomal45Ca uptake is ATP‐dependent. NaN3and mitochondrial inhibitors have no influence on microsomal45Ca uptake, which is stimulated several‐fold by oxalate.The results support the assumption, that in the guinea pig pancreas Ca mobilization from intracellular stores is necessary to initiate secretion. Due to their ability for an active accumulation of45Ca both mitochondria and microsomes could serve as intracellular calcium stores.