AJP - Gastrointestinal and Liver Physiology, Vol 266, Issue 4 613-G623, Copyright © 1994 by American Physiological Society

ARTICLES

Thapsigargin defines roles of Ca2+ in initial, sustained, and potentiated stimulation of pepsinogen secretion

Y. Kitsukawa, C. Felley, D. C. Metz and R. T. Jensen
Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.

The roles of Ca2+ in agonist-induced pepsinogen secretion from guinea pig chief cells remain unclear. We used cholecystokinin octapeptide (CCK-8) or secretin alone or with thapsigargin (TG) to clarify these roles. TG releases Ca2+ from intracellular stores by inhibiting microsomal Ca(2+)-adenosinetriphosphatase (ATPase), thereby depleting intracellular Ca2+ (Cai2+) stores. In most cells TG also causes Ca2+ influx. In the present study, with an extracellular Ca2+ concentration ([Ca2+]o) of 1.5 mM, CCK-8 (0.1 microM) caused a rapid increase in pepsinogen secretion; however, the rate decreased with time. With [Ca2+]o = 0, the initial increase was similar but later secretion was abolished, suggesting that Ca2+ influx was important for sustained secretion. With [Ca2+]o = 1.5 mM, TG (0.1 microM) caused a 2.7-fold sustained increase in in Cai2+ concentration ([Ca2+]i) and a ninefold sustained increase in pepsinogen secretion. With [Ca2+]o = 0, TG caused a transient 66% increase in [Ca2+]i and a 50% increase in pepsinogen secretion. The time course of TG-induced pepsinogen secretion correlated with the time course of TG-induced increases in [Ca2+]i. These data demonstrated that Ca2+ influx itself was a potent stimulant of pepsinogen secretion. We further focused on the roles of increasing [Ca2+]i from Cai2+ stores. With or without extracellular Ca2+ (Cao2+) present, addition of CCK-8 (0.1 microM) 10 min after TG caused no further increase in [Ca2+]i, demonstrating depletion of the inositol 1,4,5-trisphosphate-sensitive pool. The Ca(2+)-mobilizing agent CCK-8 caused no pepsinogen secretion 10 min after TG preincubation, demonstrating that mobilization of Ca2+ from intracellular stores was important in the rapid initial phase stimulation of pepsinogen secretion caused by CCK-8. In contrast, preincubation with TG had no effect on pepsinogen secretion by secretin, an agent that increases adenosine 3',5'-cyclic monophosphate. A 6-min preincubation with TG potentiated the subsequent stimulation of pepsinogen secretion caused by secretin in the presence of Cao2+ where [Ca2+]i remained elevated. However, TG-induced potentiations of secretin-stimulated pepsinogen secretion was abolished once [Ca2+]i had returned to the basal level in the absence of Cao2+.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				S. Kimura, H. Mieno, K. Tamaki, M. Inoue, and K. Chayama Nonselective cation channel as a Ca2+ influx pathway in pepsinogen-secreting cells of bullfrog esophagus Am J Physiol Gastrointest Liver Physiol, August 1, 2001; 281(2): G333 - G341. [Abstract] [Full Text] [PDF]

				D. Bosco, C. Gonelle-Gispert, C. B. Wollheim, P. A. Halban, and D. G. Rouiller Increased Intracellular Calcium Is Required for Spreading of Rat Islet {beta}-Cells on Extracellular Matrix Diabetes, May 1, 2001; 50(5): 1039 - 1046. [Abstract] [Full Text]

				J. A. Tapia, H. A. Ferris, R. T. Jensen, and L. J. Garcia Cholecystokinin Activates PYK2/CAKbeta by a Phospholipase C-dependent Mechanism and Its Association with the Mitogen-activated Protein Kinase Signaling Pathway in Pancreatic Acinar Cells J. Biol. Chem., October 29, 1999; 274(44): 31261 - 31271. [Abstract] [Full Text] [PDF]

				F. W. Hopf, P. Reddy, J. Hong, and R. A. Steinhardt A Capacitative Calcium Current in Cultured Skeletal Muscle Cells Is Mediated by the Calcium-specific Leak Channel and Inhibited by Dihydropyridine Compounds J. Biol. Chem., September 13, 1996; 271(37): 22358 - 22367. [Abstract] [Full Text] [PDF]