Regulation of cytosolic free Ca2+ concentration in acinar cells of rat pancreas

Abstract

Ca2+ uptake into isolated exocrine pancreatic cells with highly permeable plasma membrane was determined by measuring the decrease in free Ca2+ concentration of the surrounding incubation medium with a Ca2+-specific electrode. In the presence of Mg-ATP and respiratory substrates the free Ca2+ concentration of the incubation medium decreased rapidly after addition of leaky cells until a stable medium free Ca2+ concentration of 4.2 +/- 0.1 X 10(-7) mol/l was obtained. Changes in the medium free Ca2+ concentration at steady state by addition of Ca2+ or EGTA were buffered by cellular uptake or release, respectively, until the steady-state free Ca2+ concentration was reestablished. When nonmitochondrial Ca2+ uptake was determined in the presence of a combination of mitochondrial inhibitors (10(-5) mol/l antimycin, 5 X 10(-6) mol/l oligomycin, and 10(-2) mol/l azide), the rate of uptake was considerably reduced, while the steady-state concentration was unaltered. In contrast, mitochondrial uptake that could be observed in the presence of the ATPase inhibitor vanadate (2 X 10(-3) mol/l) proceeded at the same rate as the control, but the minimal medium free Ca2+ concentration reached was 2.4 +/- 0.1 X 10(-7) mol/l higher than the control. Addition of secretagogues at steady-state free Ca2+ concentration resulted in a Ca2+ release of 0.73 +/- 0.08 nmol/mg protein. The increase in medium free Ca2+ concentration was entirely transient and followed by reuptake to the prestimulation level. The data indicate that a cytosolic free Ca2+ concentration of 4 X 10(-7) mol/l can be regulated in pancreatic acinar cells by a nonmitochondrial Mg2+-dependent Ca2+ pool.

Tmp21 and p24A, Two Type I Proteins Enriched in Pancreatic Microsomal Membranes, Are Members of a Protein Family Involved in Vesicular Trafficking

“…Acinar cells were isolated from rat pancreas by collagenase digestion (Streb and Schulz, 1983). Zymogen granules were prepared from isolated acinar cells on a Percoll gradient as described (Fuller et al, 1989).…”

Evidence for the direct action of gastrin-releasing peptide(GRP) on amylase secretion from rat pancreatic acini. An assessment using a perifusion system.

“…It has been postulated that stimulation of enzyme secretion from the exocrine pancreas is triggered by an increase in levels of Cat + in the cytosol. The released Cat + derives from intracellular pools (STREB and SCHULTZ, 1983). Inositol 1,4,5-trisphosphate releases Cat + from the endoplasmic reticulum , and diacylgly- cerol activates protein kinase C, in Cat +-dependent manner (WHOOTEN and WRENN, 1984;NoGUCHi et al, 1985).…”

Interaction between secretin and nerve‐mediated amylase secretion in the isolated exocrine rat pancreas

“…After the loading period the tissue was washed twice with cold KH solution containing 2 mM EGTA, weighed and dissolved in 400 #u1 Soluene (Beckman Instruments (UK Ltd), High Wycombe, Bucks, UK). The activity of 45Ca2l in tissue was determined by scintillation analysis (Francis, Lennard & Singh, 1990) (Streb & Schulz, 1983;. Pancreatic acinar cells were loaded with either 2 uM fura-2 AM or 2 /M mag-fura-2 AM by methods described previously (Lennard & Singh, 1991.…”