Effect of W-7 on ionic fluxes and electrical activity of mouse pancreatic islets.

W-7 (N-(6-amino-hexyl)-5-chloro-1-naphthalenesulfonamide) (0.1 mM), a calmodulin inhibiting compound, suppressed the reincrease of 86Rb+ efflux from pancreatic islets normally seen in response to lowering the glucose concentration from stimulated to basal value. Ionophore (A23187)-induced increase was completely abolished. W-7 inhibited 45Ca2+ uptake and stimulation of 45Ca2+ efflux in response to glucose (11.1 mM) but did not affect K+ (20 mM)-induced 45Ca2+ uptake. Electrical activity of B-cells at 11.1 mM glucose showed a prolongation in burst length in the presence of 0.1 mM W-7. The data suggest that W-7 affects the opening properties of K+ channels resulting in a delayed repolarisation of the cells possibly through its inhibitory action on Ca2(+)-activated calmodulin.