EFFECTS OF VALINOMYCIN ON OSMOTIC LYSIS OF ZYMOGEN GRANULES AND AMYLASE EXOCYTOSIS FROM PAROTID ACINI

The role of osmotic swelling of the secretory granules in adenosine 3' ,5'-cyclic monophosphate (cAMP)-mediated amylase exocytosis was evalua ted by use of isolated zymogen granules and saponin-permeabilized acin i of the rat parotid gland. The osmotic lysis of the isolated granules was markedly enhanced by the addition of valinomycin (>10(-9) M) in t he presence of isosmotic KSCN or KI medium. However, valinomycin (up t o 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 n ot affect the granule lysis. Valinomycin alone had no effect on amylas e release from saponin-permeabilized parotid acini incubated in KCl me dium, but completely abolished cAMP-mediated amylase release in all K media used. The inhibition was clearly detected at 0.1 muM valinomyci n in KCl medium, not blocked by the addition of 1 mM MgATP to the medi um, and was greatly reduced in NaCl medium. cAMP-evoked amylase releas e was completely inhibited by SCN- and I- (permeant anions), the mean inhibitory dosages of which were approximately 25 and 50 mM, respectiv ely. These results suggest that 1) the membrane of parotid zymogen gra nules has no detectable Cl- channels responsible for osmotic swelling of the granules, and 2) increase in K+ or anion conductance of the gra nule does not enhance but inhibits cAMP-mediated amylase exocytosis fr om parotid acini.