Intracellular calcium activity in split frog skin epithelium: Effect of cAMP

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Abstract
Measurement of intracellular calcium activity (a Ca c ) by ion-selective microelectrodes has previously been technically limited to relatively large cells (≳20 μm). We now report results obtained with this technique in the small epithelial cells (≲10 μm) of split frog skin using microelectrodes having an outer tip diameter of 2+-selective microelectrodes (E Ca sc ) and with reference micropipettes (ψ sc ) either sequentially or simultaneously in 15 successful experiments. Under baseline conditions,a Ca c was measured to be 215±39nm (mean±se), in close agreement with the mean values estimated from published data obtained withNecturus proximal tubule. Stimulation of Na+ transport across six skins with 1mm serosal 8p-chlorophenylthio-3′,5′ cyclic AMP (CPTcAMP) increaseda Ca c by a factor of 2.6±0.6. The increase ina Ca c preceded the CPTcAMP-induced increase inI sc. The results of the present study indicate that electrometric determination of intracellular calcium activity is now feasible in a much wider range of cell systems than heretofore possible. CPT cAMP elevates intracellular Ca2+ activity; this phenomenon is an early event, preceding the natriferic effect of CPTcAMP.