Separation of M‐like current and ERG current in NG108‐15 cells

Differentiated NG108‐15 neuroblastoma×glioma hybrid cells were whole‐cell voltage‐clamped. Hyperpolarizing pulses, superimposed on a depolarized holding potential (−30 or −20 mV), elicited deactivation currents which consisted of two components, distinguishable by fitting with two exponential functions. Linopirdine [DuP 996, 3,3‐bis(4‐pyridinylmethyl)‐1‐phenylindolin‐2‐one), a neurotransmitter‐release enhancer known as potent and selective blocker of the M‐current of rat sympathetic neurons, in concentrations of 5 or 10 μ M selectively inhibited the fast component (IC 50 =14.7 μ M ). The slow component was less sensitive to linopirdine (IC 50 >20 μ M ). The class III antiarrhythmics [(4‐methylsulphonyl)amido]benzenesulphonamide (WAY‐123.398) and 1‐[2‐(6‐methyl‐2‐pyrydinil)ethyl]‐4‐(4‐methylsulphonylaminobenzoyl) piperidine (E‐4031), selective inhibitors of the inwardly rectifying ERG ( ether‐à‐go‐go ‐related gene) potassium channel, inhibited predominantly the slow component (IC 50 =38 n M for E‐4031). The time constant of the WAY‐123.398‐sensitive current resembled the time constant of the slow component in size and voltage dependence. Inwardly rectifying ERG currents, recorded in K + ‐rich bath at strongly negative pulse potentials, resembled the slow component of the deactivation current in their low sensitivity to linopirdine (28% inhibition at 50 μ M ). The size of the slow component varied greatly between cells. Accordingly, varied the effect of WAY‐123.398 on deactivation current and holding current. RNA transcripts for the following members of the ether‐à‐go‐go gene (EAG) K + channel family were found in differentiated NG108‐15 cells: ERG1, ERG2, EAG1, EAG‐like (ELK)1, ELK2; ERG3 was only present in non‐differentiated cells. In addition, RNA transcripts for KCNQ2 and KCNQ3 were found in differentiated and non‐differentiated cells. We conclude that the fast component of the deactivation current is M‐like current and the slow component is deactivating ERG current. The molecular correlates are probably KCNQ2/KCNQ3 and ERG1/ERG2, respectively.British Journal of Pharmacology (1999) 127 , 1213–1223; doi: 10.1038/sj.bjp.0702642