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Am J Physiol Gastrointest Liver Physiol 264: G895-G901, 1993;
0193-1857/93 $5.00
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AJP - Gastrointestinal and Liver Physiology, Vol 264, Issue 5 895-G901, Copyright © 1993 by American Physiological Society

ARTICLES

Effects of valinomycin on osmotic lysis of zymogen granules and amylase exocytosis from parotid acini

T. Takuma, T. Ichida, K. Okumura, Y. Sasaki and M. Kanazawa
Department of Oral Biochemistry, School of Dentistry, Higashi Nippon Gakuen University, Hokkaido, Japan.

The role of osmotic swelling of the secretory granules in adenosine 3',5'-cyclic monophosphate (cAMP)-mediated amylase exocytosis was evaluated by use of isolated zymogen granules and saponin-permeabilized acini of the rat parotid gland. The osmotic lysis of the isolated granules was markedly enhanced by the addition of valinomycin (> 10(-9) M) in the presence of isosmotic KSCN or KI medium. However, valinomycin (up to 10(-5) M) did not increase the granule lysis in KCl medium, although the granules were slightly less stable in KCl medium than in K2SO4 or potassium gluconate medium. Guanosine 5'-O-(3-thiotriphosphate) did not affect the granule lysis. Valinomycin alone had no effect on amylase release from saponin-permeabilized parotid acini incubated in KCl medium, but completely abolished cAMP-mediated amylase release in all K+ media used. The inhibition was clearly detected at 0.1 microM valinomycin in KCl medium, not blocked by the addition of 1 mM MgATP to the medium, and was greatly reduced in NaCl medium. cAMP-evoked amylase release was completely inhibited by SCN- and I- (permeant anions), the mean inhibitory dosages of which were approximately 25 and 50 mM, respectively. These results suggest that 1) the membrane of parotid zymogen granules has no detectable Cl- channels responsible for osmotic swelling of the granules, and 2) increase in K+ or anion conductance of the granule does not enhance but inhibits cAMP-mediated amylase exocytosis from parotid acini.


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[Abstract] [Full Text] [PDF]


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