Heterogeneous expression of voltage-gated potassium channels of the shakerfamily (Kv1) in oligodendrocyte progenitors

Outwardly rectifying K+ channels determine the membrane conductance and inf luence the proliferation rate of glial progenitor cells. To analyte the mol ecular identity and the functional role of K+ channels in glial progenitors of mouse brain, expression of shaker-type Kv1 genes was studied at three l evels: (1) presence of Kv1 mRNAs, (2) biosynthesis of channel proteins and (3) electrophysiological and pharmacological properties of K+ currents. mRN A expression of Kv1.1 to Kv1.6 genes was studied by single-cell reverse tra nscription-mediated polymerase chain reaction (RT-PCR) using degenerate pri mers to amplify the six Kv1 transcripts. Most cells expressed several mRNA combinations simultaneously. In more than half of the cells, messages for K v1.2, Kv1.5 and Kv1.6 were found, while Kv1.1, Kv1.3 and Kv1.4 were detecte d in only a minority of cells. In contrast, at the level of protein express ion - employing immunocytochemistry with subtype-specific antibodies - Kv1. 2 and Kv1.3 were undetectable (< 2%), while almost all cells expressed Kv1. 4 (85%), Kv1.5 (99%) and Kv1.6 (99%). Kv1.1 was present in a minor cell pop ulation (10%). Functional contribution of Kv1 proteins to progenitor membra ne conductance was determined by analyzing the voltage-dependence of K+ cur rent activation and inactivation as well as their current sensitivities to the subtype-preferring blockers and toxins tetraethylammonium (TEA), 4-amin opyridine (4-AP), charybdoroxin (CTX), alpha-dendrotoxin (DTX) and mast-cel l degranulating peptide (MCDP). From these results, it is concluded: first, glial progenitor cells can express all transcripts of the six Kv1 genes, b ut do not express all proteins; second, Kv1.4, Kv1.5 and Kv1.6 proteins are most abundant and were found in the majority of cells; and third, K+ curre nts flow predominantly either through heteromeric channel complexes or thro ugh homomeric Kv1.5 ion pores, but not through homomeric Kv1.4 or Kv1.6 cha nnels. (C) 1999 Elsevier Science B.V. All rights reserved.