Evidence for modulation of cell‐to‐cell electrical coupling by cAMP in mouse islets of Langerhans

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Abstract
The effects of forskolin on electrical coupling among pancreatic β‐cells were studied. Two microelectrodes were used to measure membrane potentials simultaneously in pairs of islet β‐cells. Intracellular injection of a current pulse (ΔI) elicited a membrane response ΔV 1 in the injected cell and also a response ΔV 2 in a nearby β‐cell confirming the existence of cell‐to‐cell electrical coupling among islet β‐cells. In the presence of glucose (7 mM), application of forskolin evoked a transient depolarization of the membrane and electrical activity suggesting that the drug induced a partial inhibition of the β‐cell membrane K+ conductance. Concomitant with this depolarization of the membrane there was a marked decrease in β‐cell input resistance (ΔV 2/ΔI) suggesting that exposure to forskolin enhanced intercellular coupling. Direct measurements of the coupling ratio ΔV 2/ΔV 1 provided further support to the idea that forskolin enhances electrical coupling among islet cells. Indeed, application of forskolin reversibly increased the coupling ratio. These results suggest that cAMP might be involved in the modulation of electrical coupling among islet β‐cells.