AJP - Cell Physiology, Vol 254, Issue 5 C621-C627, Copyright © 1988 by American Physiological Society
Kinetics of high-affinity Ca2+ sequestration in permeabilized rat pancreatic acini
T. W. Hurley
Department of Child Health, University of Missouri School of Medicine, Columbia 65212.
Energy-dependent subcellular Ca2+ sequestration was studied in the presence
of ruthenium red using rat pancreatic acini, which had been permeabilized
by exposure to medium nominally free of Ca2+. The initial rate of Ca2+
uptake (approximately 2,800 pmol.min-1.mg acinar protein-1) quickly slowed,
and a mean steady-state Ca2+ content of approximately 3,000 pmol/mg was
reached after 5-10 min of incubation at 37 degrees C. Ca2+ uptake was
stimulated by submicromolar Ca2+ concentrations (K0.5 = 156 nM); required
Mg2+-ATP (K0.5 = 0.78 mM) was greatest at a pH of 7.0 and was abolished by
the Ca2+ ionophore A23187. Other nucleotide phosphates as well as
p-nitrophenylphosphate were relatively poor substrates, supporting Ca2+
uptake at initial rates that were 6-14% of those measured in the presence
of ATP. These results show that pancreatic acini permeabilized without
detergents possess a nonmitochondrial Ca2+ transporting system not located
in the plasma membrane but with the properties expected of a major
regulator of acinar cytosolic Ca2+ concentration.
