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Am J Physiol Cell Physiol 267: C255-C265, 1994;
0363-6143/94 $5.00
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AJP - Cell Physiology, Vol 267, Issue 1 C255-C265, Copyright © 1994 by American Physiological Society

ARTICLES

Potentiation of Ca(2+)-activated secretory activity by a cAMP-mediated mechanism in avian salt gland cells

S. C. Martin, J. Thompson and T. J. Shuttleworth
Department of Physiology, University of Rochester School of Medicine and Dentistry, New York 14642.

In the avian salt gland carbachol (CCh) evokes oscillations in K+ and Cl- current that are sufficient to fully activate secretory activity. Employing the perforated patch-clamp technique, we demonstrate that beta-adrenergic receptor activation stimulates a sustained adenosine 3',5'-cyclic monophosphate (cAMP)-dependent Cl- current with no increase in K+ current. This evokes only a modest increase in secretory activity. However, application of isoproterenol in the presence of a threshold dose of CCh results in maximal secretory activity. Membrane potential measurements demonstrate that isoproterenol stimulates a sustained membrane depolarization from approximately -45 mV to the Cl- equilibrium potential (ECl), whereas CCh evokes oscillations in membrane potential to levels more negative than ECl, representing a mixture of K+ and Cl- conductances. We conclude that, in agreement with current models of fluid secretion, maximal stimulation can only be achieved with simultaneous activation of both K+ and Cl- currents. Because isoproterenol fails to stimulate a K+ current, Cl- secretion is reduced as the driving force for Cl- secretion is dissipated. However, if a driving force is imposed by increasing K+ channel activity (by coadministering CCh), Cl- efflux is sustained. These results could provide a basis for the marked potentiation of Ca(2+)-mediated secretion by agonists that increase cAMP seen in in vivo studies of salivary glands and other exocrine tissues.


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J.-P. Hildebrandt, R. Gerstberger, and M. Schwarz
In vivo and in vitro induction of c-fos in avian exocrine salt gland cells
Am J Physiol Cell Physiol, October 1, 1998; 275(4): C951 - C957.
[Abstract] [Full Text] [PDF]


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