Control of Ca2+ wave propagation in mouse pancreatic acinar cells.
We have investigated control mechanisms involved in the propagation of agonist-induced Ca2+ waves in isolated mouse pancreatic acinar cells. Using a confocal laser-scanning microscope, we were able to show that maximal stimulation of cells with acetylcholine (ACh, 500 nM) or bombesin (1 nM) caused an initial Ca2+ release of comparable amounts with both agonists at the luminal cell pole. Subsequent Ca2+ spreading to the basolateral membrane was faster with ACh (17.3 +/- 5.4 microns/s) than with bombesin (8.0 +/- 2.2 microns/s). The speed of bombesin-induced Ca2+ waves could be increased up to the speed of ACh-induced Ca2+ waves by inhibition of protein kinase C (PKC). Activation of PKC significantly decreased the speed of ACh-induced Ca2+ waves but had only little effect on bombesin-evoked Ca2+ waves. Within 3 s after stimulation, production of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] was higher in the presence of ACh compared with bombesin, whereas bombesin induced higher levels of diacylglycerol (DAG) than ACh. These data suggest that the slower propagation speed of bombesin-induced Ca2+ waves is due to higher activation of PKC in the presence of bombesin compared with ACh. The higher increase in bombesin-compared with ACh-induced DAG production is probably due to activation of phospholipase D (PLD). Inhibition of the PLD-dependent DAG production by preincubation with 0.3% butanol led to an acceleration of the bombesin-induced Ca2+ wave. In further experiments, we could show that ruthenium red (100 microM), an inhibitor of Ca(2+)-induced Ca2+ release in skeletal muscle, also decreased the speed of ACh-induced Ca2+ waves. The effect of ruthenium red was not additive to the effect of PKC activation. From the data, we conclude that, following Ins(1,4,5)P3-induced Ca2+ release in the luminal cell pole, secondary Ca2+ release from stores, which are located in series between the luminal and the basal plasma membrane, modifies Ca2+ spreading toward the basolateral cell side by Ca(2+)-induced Ca2+ release. Activation of PKC leads to a reduction in Ca2+ release from these stores and therefore could explain the slower propagation of Ca2+ waves in the presence of bombesin compared with ACh.
Pfeiffer
F
F
Institute of Physiology II, University of the Saarland, Homburg, Germany.
Sternfeld
L
L
Schmid
A
A
Schulz
I
I
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006873:Hydroquinones / Q000494:pharmacology; D007202:Indicators and Reagents / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008297:Male; D051379:Mice; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D010507:Periodicity; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D012430:Ruthenium Red / Q000494:pharmacology; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism
D015220:Calcium Channels; D004791:Enzyme Inhibitors; D006873:Hydroquinones; D007202:Indicators and Reagents; D019269:Phosphatidylinositol 4,5-Diphosphate; D012430:Ruthenium Red; D015544:Inositol 1,4,5-Trisphosphate; C018855:2-tert-butylhydroquinone; D011493:Protein Kinase C; D010738:Type C Phospholipases; D000252:Calcium-Transporting ATPases; D000109:Acetylcholine; D001839:Bombesin; D002118:Calcium