Sequence and functional expression in Xenopus oocytes of a human insulinoma and islet potassium channel.
 Regulation of insulin secretion involves the coordinated control of ion channels in the beta-cell membrane.
 We have isolated and characterized cDNA and genomic clones encoding a voltage-dependent K+ channel isoform expressed in human islets and in a human insulinoma.
 This K+ channel isoform, designated hPCN1, with a deduced amino acid sequence of 613 residues (Mr = 67,097), is related to the Shaker family of Drosophila K+ channels.
 hPCN1 is homologous to two other human K+ channel isoforms we have isolated, hPCN2 and hPCN3, with 55% and 65% amino acid sequence identity, respectively.
 The electrophysiological characteristics of hPCN1 were determined after microinjection of synthetic RNA into Xenopus oocytes.
 Two-microelectrode voltage-clamp recordings of oocytes injected with hPCN1 RNA revealed a voltage-dependent outward K+ current that inactivated slowly with time.
 Outward currents were inhibited by 4-aminopyridine with a Ki less than 0.10 mM and were relatively insensitive to tetraethylammonium ion or Ba2+.
 A delayed rectifier K+ channel such as hPCN1 could restore the resting membrane potential of beta cells after depolarization and thereby contribute to the regulation of insulin secretion.
