Effects of pyridine nucleotides on the gating of ATP-sensitive potassium channels in insulin-secreting cells.

The single-channel current recording technique has been used to study the influences that the pyridine nucleotides NAD, NADH, NADP and NADPH have on the gating of ATP-sensitive K+ channels in an insulin-secreting cell line (RINm5F). The effects of the nucleotides were studied at the intracellular surface using either excised inside-out membrane patches or permeabilized cells. All four pyridine nucleotides were found to evoke similar effects. At low concentrations, 100 microM and less, each promoted channel opening whereas high concentrations, 500 microM and above, evoked channel closure. The degree of K+ channel activation by pyridine nucleotides (low conc.) was found to be similar to that evoked by the same concentrations of ADP or GTP, whereas the degree of K+ channel inhibition (high conc.) was less marked than that evoked by the same concentrations of ATP, and never resulted in refreshment of K+ channels following removal. The effects of NAD, NADH, NADP and NADPH seemed to interact with those of ATP and ADP. In the presence of 1 mM ADP and 4 mM ATP, 10 to 100 microM concentrations of the pyridine nucleotides could not evoke channel opening, whereas concentrations of 500 microM and above were found to evoke channel closure. In the presence of 2 mM ATP and 0.5 mM ADP, however, 10 to 100 microM concentrations of the pyridine nucleotides were able to activate K+ channels.