Single channel recordings of potassium currents in an insulin-secreting cell line

Using the patch-clamp technique we observed three distinct classes of K+ channels which were spontaneously active in excised 'inside-out' membrane patches from an insulin-secreting rat pancreatic islet cell line (CRI-G1). Two of these occurred infrequently, one with a conductance of approximately 7 pS, and the other a conductance of 220 pS. The activation of the 220 pS K+ channel was dependent upon the membrane voltage and was sensitive to the concentration of calcium ions at the cytoplasmic surface of the membrane. The third, and by far the most common class of K+ channel, was characterized by its sensitivity to ATP. Application of ATP to the cytoplasmic side of the membrane reversibly inhibited this K+ channel in a dose-dependent manner, but had no effect when applied to the external side. The properties of the ATP-sensitive K+ channel appear to be indistinguishable from those of a channel found in rat neonatal beta cells. Thus this insulin-secreting cell line should prove valuable in the investigation of the role of K+ channels in the regulation of insulin secretion.