Adamantane derivatives: a new class of insulin secretagogues.

Adamantane derivatives were found to increase insulin release in vitro. Mouse islets were used to study the mechanisms and molecular requirements of that hitherto unrecognised property. At a non-stimulatory concentration of glucose (3 mM), 1-adamantanamine (1 mM) reversibly inhibited 86Rb efflux from islet cells, depolarized the beta-cell membrane, induced electrical activity, stimulated 45Ca uptake and efflux, and triggered insulin release. Omission of extracellular Ca2+ abolished the secretory response but only partially inhibited the acceleration of 45Ca efflux. At a stimulatory concentration of glucose (10 mM), 1-adamantanamine reversibly increased 86Rb efflux, potentiated electrical activity (lengthening of the slow waves with spikes), augmented 45Ca uptake and efflux, and increased insulin release. The effects of adamantanamine were dose-dependent, with a threshold concentration of 10 microM for stimulation release. 2-Adamantanamine was as potent as 1-adamantanamine. In contrast, substitution of the amino group by a carboxyl group (1-adamantanecarboxylic acid) decreased the effectiveness by about 65%, and substitution by a hydroxyl group (1-adamantanol) suppressed it. It is concluded that adamantane derivatives bearing an amino group decrease K+ permeability of the beta-cell membrane and thereby cause depolarization. This activates voltage-dependent Ca channels, permits Ca2+ influx and eventually stimulates insulin release. They may also mobilize cellular Ca2+, but this effect is not sufficient to cause release.