Evidence against direct involvement of cyclic AMP-dependent protein phosphorylation in the exocytosis of amylase.
To examine whether or not the activation of cyclic AMP-dependent protein kinase is coupled to the exocytosis of amylase from rat parotid cells, the effect of protein kinase inhibitors on amylase release and protein phosphorylation was studied. A membrane-permeable inhibitor of cyclic AMP-dependent protein kinase, N-[2-(methylamino)ethyl]-5-isoquinolinesulphonamide (H-8), and peptide fragments of the heat-stable protein kinase inhibitor [PKI-(5-24)-peptide and PKI-(14-24)-amide] strongly inhibited cyclic AMP-dependent protein kinase activity in the cell homogenate. However, H-8 had no inhibitory effect on amylase release from either intact or saponin-permeabilized parotid cells stimulated by isoproterenol or cyclic AMP. Moreover, PKI-(5-24)-peptide and PKI-(14-24)-amide did not inhibit cyclic AMP-evoked amylase release from saponin-permeabilized cells, whereas cyclic AMP-dependent phosphorylations of 21 and 26 kDa proteins in intact or permeabilized cells were markedly inhibited by these inhibitors. These results suggest that cyclic AMP-dependent protein phosphorylation is not directly involved in the exocytosis of amylase regulated by cyclic AMP.
Takuma
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Department of Oral Biochemistry, School of Dentistry, Higashi Nippon Gakuen University, Hokkaido, Japan.
D000681:Amylases / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects*; D047908:Intracellular Signaling Peptides and Proteins; D007546:Isoquinolines / Q000494:pharmacology; D010306:Parotid Gland / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D051381:Rats
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007546:Isoquinolines; D047428:Protein Kinase Inhibitors; C015482:protein kinase modulator; C053177:N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide; D000242:Cyclic AMP; D000681:Amylases