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 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.
Takuma
T
T
Department of Oral Biochemistry, School of Dentistry, Higashi Nippon Gakuen University, Hokkaido, Japan.
Ichida
T
T
Okumura
K
K
Sasaki
Y
Y
Kanazawa
M
M
D000681:Amylases / Q000378:metabolism*; D000818:Animals; D000838:Anions; D002458:Cell Fractionation; D002463:Cell Membrane Permeability; D002499:Centrifugation, Density Gradient; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000648:ultrastructure*; D004533:Egtazic Acid / Q000494:pharmacology; D004792:Enzyme Precursors / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007700:Kinetics; D010306:Parotid Gland / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D017208:Rats, Wistar; D012503:Saponins; D014634:Valinomycin / Q000494:pharmacology*
D000838:Anions; D004792:Enzyme Precursors; D012503:Saponins; D014634:Valinomycin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D000242:Cyclic AMP; D000681:Amylases