KCl-induced insulin secretion from RINm5F cells is mediated through Ca2+ influx along L-type Ca2+ channels

Summary In order to characterize the voltage-dependent Ca²⁺ channels of insulin secretory RINm 5F cells, we have studied the binding of the dihydropyridine (DHP) type Ca²⁺ antagonist PN 200-110 and its effect on insulin release. In the membrane preparation from RINm 5F cells [³H]-(+)-PN 200-110 bound to a high affinity binding site in a stereoselective manner (KD: 7.0 nM, B_max: 858 fmol/mg protein). The benzothiazepine type Ca²⁺ antagonist D-cis-diltiazem increased the binding of [³H]-(+)-PN 200-110 in a temperature-dependent manner. The phenylalkylamine-type Ca²⁺ antagonist verapamil decreased PN binding with an IC₅₀ of 100 M. (+)-PN 200-110 inhibited KCl-(25 mM)-induced insulin release (IC₅₀ = 10 nM), Effects on binding and hormone release occurred over comparable concentration ranges: 1 M PN 200-110 produced 100% displacement and totally abolished depolarization-mediated insulin release. The N-type Ca²⁺-antagonist -conotoxin showed no effect on KCl-induced insulin release. The data suggest that in RINm 5 F cells only l-type Ca²⁺ channels are involved in the mechanism of depolarization-mediated insulin release.Some of the data reported here were presented at the 27th Annual Meeting of the European Association for the Study of Diabetes, Dublin, 10–14 September 1991Correspondence to: H. Safayhi at the above address