Nucleotide-sensitive ion channels in human insulin producing tumour cells

Cells from a human insulin producing tumour have been studied and single channel currents recorded. We have observed three main cation-selective channels in excised patch experiments. An ATP-sensitive potassium channel is present the activity of which can be inhibited by the oral hypoglycaemic drug, tolbutamide. A calcium-activated nonselective cation channel, which is inhibited by AMP could also be seen. In addition a large conductance potassium selective channel, possibly the "maxi" calcium-activated potassium channel is present in these cells.