AJP - Gastrointestinal and Liver Physiology, Vol 245, Issue 3 347-G357, Copyright © 1983 by American Physiological Society
Regulation of cytosolic free Ca2+ concentration in acinar cells of rat pancreas
H. Streb and I. Schulz
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.
