Identification of RBK1 potassium channels in C6 astrocytoma cells.
Ionic currents in C6 astrocytoma cells were studied using the patch clamp technique under the whole cell configuration. A delayed rectifier K+ current with an amplitude of approximately 1 nA at +50 mV was observed in 86% (92/107) of the cells examined. This K+ current resembled the delayed rectifier present in type-1 and type-2 astrocytes in vitro and could be inhibited by a variety of K+ channel blockers, including TEA (IC50:0.5 mM), 4-aminopyridine (IC50:0.2 mM), MCD peptide (IC50:52 nM), dendrotoxin I (IC50:9 nM), and charybdotoxin (74% inhibition at 50 nM). Northern blot analysis, cloning of cDNA and subsequent sequencing showed that the C6 cell delayed rectifier K+ channel is equivalent to the RBK1 K+ channel derived from a rat brain cDNA library. The level of RBK1 transcripts in C6 cells was comparable to that reported in rat brain. The C6 delayed rectifier K+ channel is probably a homomeric RBK1 K+ channel judging from its pharmacological properties which are similar to the RBK1 channel expressed in Xenopus oocytes. Some C6 cells also expressed a transiently activated outward K+ current (IA). This current was found in less than 50% of the cells and in general contributed no more than 8% of the total outward current. No voltage-dependent inward Na+ or Ca2+ currents or inwardly rectifying K+ currents were observed in over 100 C6 cells examined. The present results show that the dominant voltage gated ionic current in C6 cells is the RBK1 delayed rectifier K+ channel.(ABSTRACT TRUNCATED AT 250 WORDS)
Wang
S Y
SY
Department of Biology, SUNY at Albany 12222.
Castle
N A
NA
Wang
G K
GK
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D001254:Astrocytoma; D004247:DNA / Q000235:genetics; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000302:isolation & purification; D051381:Rats; D014407:Tumor Cells, Cultured
D015221:Potassium Channels; D012333:RNA, Messenger; D004247:DNA