ATP-sensitive K+ channels in an insulin-secreting cell line are inhibited by D-glyceraldehyde and activated by membrane permeabilization.

The control of K+ channels in the insulin-secreting cell line RINm5F has been investigated by patch-clamp single-channel current recording experiments. The unitary current events recorded from cell-attached patches are due to large and small inwardly rectifying ATP-sensitive K+ channels with conductance properties similar to the two channels previously identified in primary cultured rat islet cells (Findlay, I., Dunne, M.J., & Petersen, O.H. J. Membrane Biol. 88:165-172, 1985). Cell permeabilization through brief exposure to 10 microM digitonin or 0.05% saponin (outside the isolated membrane patch area) results in a dramatic increase in current through the cell-attached patch due to opening of many large and small K+-selective channels. These channels are inhibited in a dose-dependent manner by ATP applied to the bath (near-complete inhibition by 5 mM ATP). During prolonged ATP exposure (1-5 min) the initial inhibition is followed by partial recovery of channel activity, although further activation does occur when ATP is subsequently removed. From the maximal number of coincident channel openings in the permeabilized cells (in the absence of ATP), it is estimated that there are on average 12 large ATP-sensitive K+ channels per membrane patch, but in the intact cells less than 5% of the membrane patches exhibited three or more coincident K+ channel openings, indicating the degree to which the channels are inhibited in the resting condition by endogenous ATP. Stimulation of RINm5F cells to secrete insulin was carried out by challenging intact cells with 10 mM D-glyceraldehyde.(ABSTRACT TRUNCATED AT 250 WORDS)