Effect of alpha(1)-adrenergic stimulation of Cl- secretion and signal transduction in exocrine glands (Rana esculenta)

In the present work, the effect of stimulation of alpha-adrenergic receptor s on Cl- secretion via exocrine frog skin glands was investigated. The alph a-adrenergic stimulation was performed by addition of the adrenergic agonis t noradrenaline in the presence of the beta-adrenergic antagonist propranol ol. In the presence of propranolol, noradrenaline had no effect on the cell ular cAMP content. The Cl- secretion was measured as the amiloride-insensit ive short circuit current (/(SC)). Addition of noradrenaline induced a biph asic increase in the /(SC). The increase in /(SC) coincided with an increas e in the net Cl-36(-) secretion. The noradrenaline-induced increase in /(SC ) was dose-dependent with an EC50 of 13 +/- 0.3 mu M. Epifluorescence micro scopic measurements of isolated, fura-2-loaded frog skin gland acini were u sed to characterize the intracellular calcium ([Ca2+](i)) response. Applica tion of noradrenaline induced a biphasic [Ca2+](i) response, which was dose -dependent with an EC50 of 11 +/- 6 mu M. The Ca2+ plateau unlike the peak- response was sensitive to removal of Ca2+ from the extracellular medium. Th e noradrenaline-induced increase in the Cl- secretion as well as in [Ca2+]( i) was sensitive to the alpha(1)-adrenergic antagonist prazosine. Ryanadine and caffeine had no effect on [Ca2+](i) indicating that the release was in dependent of ryanodine-sensitive Ca2+ stores. Noradrenaline mediated a sign ificant increase in the cellular inositol 1,4,5-trisphosphate (IP3) content suggesting that the signal transduction pathway leading to the noradrenali ne-induced increase in Ca2+ involved IP3 and a release of Ca2+ from IP3-sen sitive stores.