Cck, carbachol, and bombesin activate distinct plc- isoenzymes via
gq/11 proteins in rat pancreatic acinar membranes.
Piiper, Albrecht, Danuta Stryjek-Kaminska, Rolf Klengel, and Stefan
Zeuzem.
II. Medical Department, University of Frankfurt, 60590 Frankfurt a.
M., Germany
APStracts 3:0166G, 1996.
Four different isoforms of phospholipase C- (PLC-1-4) have yet been
discovered, raising the important question whether a distinct
receptor activates a single PLC-[beta] isoenzyme or a subset of PLC
-[beta] isoenzymes. The present study was designed to investigate
activation of PLC- isoenzymes by three different PLC-activating
agonists which bind to different receptor entities, i. e.
cholecystokinin-octapeptide (CCK8), bombesin and carbachol in rat
pancreatic acinar membranes. PLC activity was measured using
exogenous [3H]phosphatidylinositol 4,5-bisphosphate as substrate.
Western blot analysis of pancreatic acinar membranes revealed the
presence of PLC-1, -3, -1, and -1, but not of PLC-2, -4, -2, and -2.
Preincubation of the membranes with anti-PLC-1 or -[beta]3 antibody
reduced agonist-induced activation of PLC. The order of sensitivity
towards inhibition by anti-PLC-1 antibody was CCK8 > bombesin
> carbachol. An opposite order of sensitivity was found for
inhibition of PLC activity by anti-PLC-3 antibody (carbachol >
bombesin > CCK8). Anti-PLC-2, -4, -1, -2, -1, and -2 antibodies
had no effect. Preincubation of the membranes with an antibody raised
against the C-terminus of the subunit of Gq/11 proteins inhibited PLC
activity in response to all three different receptor agonists to a
similar extent, whereas anti-Gi1-2[alpha] and anti-Gi3 antibodies had
no effect. In conclusion, the data of the present study indicate that
CCK8 and carbachol activate PLC-1 and PLC-3, respectively, whereas
bombesin activates both PLC-1 and PLC-3. Activation of PLC- by these
receptor agonists is mediated by Gq/11.
Received 19 March 1996; accepted in final form 8 August 1996.
APS Manuscript Number G97-6.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996