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Pflügers Archiv

, Volume 444, Issue 5, pp 586–596 | Cite as

Cyclic AMP has distinct effects from Ca2+ in evoking priming and fusion/exocytosis in parotid amylase secretion

  • Keiichi Yoshimura
  • Junko Fujita-Yoshigaki
  • Masataka Murakami
  • Akihisa Segawa
Original Article

Abstract.

Rat parotid acinar cells were perfused in small quartz columns to examine the role of cAMP and Ca2+ in the priming and fusion/exocytosis of amylase secretion. Carbachol (CCh) evoked a biphasic response of amylase secretion with an initial rapidly occurring large peak and a subsequent sustained plateau. Isoproterenol produced slowly increasing amylase secretion that reached the plateau greater than that induced by CCh. Combined stimulation with isoproterenol and CCh greatly potentiated amylase secretion. The rise and decay of amylase secretion induced by the combined stimulation was similar to those induced by CCh but not by isoproterenol, suggesting that the potentiation is caused by isoproterenol-induced modification of the CCh effect. Concentration-dependent responses of CCh-induced amylase secretion with and without isoproterenol showed that isoproterenol greatly enhances both the sensitivity and maximum effect of CCh. Similar potentiation was observed when the Ca2+ effect was directly examined in cells permeabilized to Ca2+ with ionomycin instead of CCh. In a Ca2+-free medium, CCh evoked an initial peak but did not produce a sustained plateau. Isoproterenol did not enhance the effect of CCh on [Ca2+]i. 2,4-Dintrophenol and carbonyl cyanide m-chlorophenyl hydrazone did not decrease the CCh-induced initial peak of amylase secretion but markedly decreased the sustained responses induced by isoproterenol and CCh. These results suggest that CCh, via Ca2+, has two distinct effects on amylase secretion: triggering of fusion/exocytosis and the priming of secretory granules. Isoproterenol, via cyclic AMP, also has two distinct effects: direct stimulation of priming and enhancement of the sensitivity to the Ca2+ effects. Thus, isoproterenol stimulates amylase secretion by increasing the primed pools of secretory granules, whereas CCh increases the flux of secretory granules into/from the primed pools, which is greatly enhanced by isoproterenol.

Amylase secretion Ca2+ Cyclic AMP Fusion/exocytosis Priming 

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Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  • Keiichi Yoshimura
    • 1
  • Junko Fujita-Yoshigaki
    • 2
  • Masataka Murakami
    • 3
  • Akihisa Segawa
    • 4
  1. 1.Department of Physiology, Hokkaido University School of Dentistry, North 13, West 7, Sapporo 060–8586, Japan
  2. 2.Department of Physiology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271–8587, Japan
  3. 3.Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki 444–8585, Japan
  4. 4.Department of Anatomy, School of Medicine, Kitasato University, Sagamihara 228–8555, Japan

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