AJP - Gastrointestinal and Liver Physiology, Vol 249, Issue 4 470-G478, Copyright © 1985 by American Physiological Society
Intracellular mediators of Na+-K+ pump activity in guinea pig pancreatic acinar cells
S. R. Hootman, D. L. Ochs and J. A. Williams
The involvement of Ca2+ and cyclic nucleotides in neurohormonal regulation
of Na+-K+-ATPase (Na+-K+ pump) activity in guinea pig pancreatic acinar
cells was investigated. Changes in Na+-K+ pump activity elicited by
secretagogues were assessed by [3H]ouabain binding and by ouabain-sensitive
86Rb+ uptake. Carbachol (CCh) and cholecystokinin octapeptide (CCK-8) each
stimulated both ouabain-sensitive 86Rb+ uptake and equilibrium binding of
[3H]ouabain by approximately 60%. Secretin increased both indicators of
Na+-K+ pump activity by approximately 40% as did forskolin, 8-bromo- and
dibutyryl cAMP, theophylline, and isobutylmethylxanthine. Incubation of
acinar cells in Ca2+-free HEPES-buffered Ringer (HR) with 0.5 mM EGTA
reduced the stimulatory effects of CCh and CCK-8 by up to 90% but caused
only a small reduction in the effects of secretin, forskolin, and cAMP
analogues. In addition, CCh, CCK-8, secretin, and forskolin each stimulated
ouabain-insensitive 86Rb+ uptake by acinar cells. The increase elicited by
CCh and CCK-8 was greatly reduced in the absence of extracellular Ca2+,
while that caused by the latter two agents was not substantially altered.
The effects of secretagogues on free Ca2+ levels in pancreatic acinar cells
also were investigated with quin-2, a fluorescent Ca2+ chelator. Basal
intracellular Ca2+ concentration ([Ca2+]i) was 161 nM in resting cells and
increased to 713 and 803 nM within 15 s after addition of 100 microM CCh or
10 nM CCK-8, respectively. Forskolin, secretin, and cAMP analogues had no
effect on [Ca2+]i, nor did they either reduce or potentiate the rise in
[Ca2+]i evoked by CCh.(ABSTRACT TRUNCATED AT 250 WORDS)
