Cyclic AMP antagonist Rp-cAMPS inhibits amylase exocytosis from saponin-permeabilized parotid acini.
Rp-cAMPS, the Rp-diastereomer of adenosine 3',5'-phosphorothioate, is often referred to as a cAMP antagonist, since it binds to the regulatory subunit of cAMP-dependent protein kinase without dissociation of free catalytic subunits. To evaluate the role of cAMP-dependent protein kinase in amylase exocytosis, we examined the effect of Rp-cAMPS on amylase release from rat parotid acini. Rp-cAMPS did not stimulate amylase release from saponin-permeabilized parotid acini, whereas its Sp-isomer strongly evoked amylase release. Rp-cAMPS dose-dependently inhibited amylase release stimulated by Sp-cAMPS. In the presence of Rp-cAMPS, the dose-response curve of Sp-cAMPS was shifted to the right. The inhibitory effect of Rp-cAMPS on isoproterenol-induced amylase release was not detected in intact acini, but was clearly observed in the permeabilized ones. Rp-cAMPS markedly inhibited protein phosphorylation evoked by Sp-cAMPS, indicating that Rp-cAMPS prevents the dissociation of cAMP-dependent protein kinase. These results, taken together with synergistic increase in amylase release by the combination of site-selective cAMP analogues [T. Takuma (1990) J. Biochem. 108, 99-102], suggest that cAMP-dependent protein kinase is involved in the exocytosis of amylase from parotid acini.
Takuma
T
T
Department of Oral Biochemistry, School of Dentistry, Higashi Nippon Gakuen University, Hokkaido.
Ichida
T
T
D000681:Amylases / Q000378:metabolism*; D000818:Animals; D000242:Cyclic AMP / Q000037:antagonists & inhibitors*; D005089:Exocytosis; D010306:Parotid Gland / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D012503:Saponins / Q000737:chemistry*; D013237:Stereoisomerism
D012503:Saponins; D000242:Cyclic AMP; D000681:Amylases