Dynamics of the cationic and secretory responses to A-4166 in perifused pancreatic islets

The dynamics of the cationic and secretory response to A-4166, a hypoglycemic meglitinide analogue, was investigated in rat islets prelabelled with either 36Rb or 45Ca and placed in a perifusion system. In the absence of D-glucose, A-4166 (10 microM) provoked an immediate, sustained and rapidly reversible inhibition of 36Rb outflow, this contrasting with a short-lived stimulation of insulin release. In the presence of 6 mM D-glucose, A-4166 provoked a rapid, sustained and rapidly reversible stimulation of both insulin release and 45Ca efflux. The latter cationic response was suppressed in the absence of extracellular Ca2+, in which case A-4166 even caused a modest decrease in effluent radioactivity. These findings support the view that A-4166 acts mainly in the islet B-cell by closing ATP-responsive K+ channels, leading to subsequent depolarization of the plasma membrane and gating of voltage-sensitive Ca2+ channels. Independently of the latter effect, A-4166 may also affect the intracellular distribution of Ca2+ ions. The present data further indicate that A-4166 belongs to those hypoglycemic agents that cause rapidly reversible changes in cationic and secretory events, at variance with highly potent sulfonylureas such as glibenclamide or glimepiride.