Amantadine and sparteine inhibit ATP-regulated K-currents in the insulin-secreting beta-cell line, HIT-T15.

1. The effects of pharmacological agents that potentiate insulin release were studied on ATP-regulated K-currents (K-ATP currents) in the insulin-secreting beta-cell line HIT-T15 by use of patch-clamp methods. 2. The tricyclic drug, 1-adamantanamine (amantadine), reversibly inhibited both whole-cell currents (with a Ki of 120 microM) and single channel currents in inside-out patches. This effect was principally due to an increase in a long closed state which reduced the channel open probability. The related compound, 1-adamantanol, in which the amino group is substituted by a hydroxyl one, did not inhibit K-ATP currents substantially. 3. The alkaloid, sparteine, reversibly inhibited both whole-cell K-ATP currents (Ki = 171 microM) and single channel currents in inside-out patches. 4. The results suggest that sparteine and amantadine can block the K-ATP channel from either side of the membrane and support the idea that at least part of the stimulatory effect of these agents on insulin secretion results from inhibition of this channel.