AJP - Cell Physiology, Vol 258, Issue 1 C54-C61, Copyright © 1990 by American Physiological Society
Regulating transient and sustained changes of cytosolic Ca2+ in rat pancreatic acini
T. W. Hurley and R. W. Brinck
Department of Child Health, University of Missouri School of Medicine, Columbia 65212.
The regulation of changes in cytosolic Ca2+ concentration (Cai2+) during
exposure to carbachol was studied in rat pancreatic acini loaded with
fura-2. With an extracellular Ca2+ concentration (Cao2+) of 2.5 mM, resting
Cai2+ is 185 +/- 48 (SD) nM (n = 23), which rises to 696 +/- 222 nM, then
falls over 2 min to a stable plateau of 401 +/- 106 nM. With Cao2+ less
than 10 nM, carbachol produces an immediate threefold increase in Cai2+
that dissipates over 2-3 min, and Cai2+ steadily falls below prestimulation
levels. Atropine prevents all responses to carbachol, and when it is added
during a response to carbachol, Cai2+ drops to resting values within
seconds. Ca2+ influx is required for the prolonged elevation of Cai2+
during carbachol exposure, but Ca2+ entry is not regulated by an increase
in Cai2+ itself nor does Ca2+ enter via voltage-gated L-type channels. The
muscarinic receptor-operated Ca2+ entry mechanism is sensitive to Cao2+,
since sustained elevations in Cai2+ are maximal at 2.5 mM Cao2+ but are
much less pronounced at lower external Ca2+ concentrations.
