AbstractIonic 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 ∼ 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 inXenopusoocytes. 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. Since C6 cells express RBK1 mRNA at a level comparable to its rat brain counterpart, these cells may be a valuable system to study the RBK1 channel and its gene e
展开▼
