Intracellular mediators of Na+-K+ pump activity in guinea pig pancreatic acinar cells.
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)
Hootman
S R
SR
Ochs
D L
DL
Williams
J A
JA
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D006168:Guinea Pigs; D007473:Ion Channels / Q000502:physiology*; D009712:Nucleotides, Cyclic / Q000494:pharmacology; D010042:Ouabain / Q000378:metabolism; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D011868:Radioisotopes / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012633:Secretin / Q000494:pharmacology; D012844:Sincalide / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*
D007473:Ion Channels; D009712:Nucleotides, Cyclic; D011868:Radioisotopes; D012633:Secretin; D005576:Colforsin; D010042:Ouabain; D000255:Adenosine Triphosphate; D002217:Carbachol; D012964:Sodium; D012844:Sincalide; D012413:Rubidium; D011188:Potassium; D002118:Calcium