A Rat Pituitary Tumour K(+) Channel Expressed in Frog Oocytes Induces a Transient K(+) Current Indistinguishable from...

A voltage-gated K(+) channel protein has been cloned from a cDNA library derived from poly(A)(+) RNA of the rat pituitary tumour cell line GH(3) /B(6) by the polymerase chain reaction technique. The clone referred to as RGHK9 encodes a protein sequence very similar to a recently cloned K(+) channel protein from rat brain and heart, with deviations in a few amino-acid positions. In situ hybridization experiments show that RGHK9 mRNA is also present in the anterior pituitary as well as in other brain regions and that it is particularly abundant in the hippocampus. After injection of cRNA transcribed from the RGHK9 cDNA clone into Xenopus oocytes, the expressed protein induces a transient K(+) current. Except for the activation kinetics the properties of this current are indistinguishable from that of the native transient K(+) current measured in GH(3) /B(6) cells, e.g. both K(+) currents are blocked by 4-aminopyridine and show the same voltage dependence and slope of steady state activation and inactivation as well as identical time constants of, and slow recovery from, inactivation. Taken together, these data show that the outward-rectifying voltage-gated K(+) channel protein encoded by the RGHK9 cDNA correlates well in its functional properties with that of a very similar, if not identical, K(+) channel present in GH(3) /B(6) cells.