SULFHYDRYL MODIFICATION INHIBITS K-CURRENT WITH KINETICS CLOSE TO ACETYLCHOLINE IN RODENT NG108-15 CELLS( (M))

The effects of sulfhydryl reagents on M-type voltage-dependent potassi um currents (I-K(M)) were examined in NG108-15 cells transformed to ex press m1 muscarinic acetylcholine receptors (mAChRs), a NGPM1-27 clone . Focal application of glutathione at millimolar concentrations dissol ved in acidic solutions caused a transient inward current in NGPM1-27 cells at holding potentials of - 30 mV, associated with an inhibition of I-K(M). The glutathione-induced response was mimicked by cysteine. These effects were also reproduced by superfusion with micromolar conc entrations of HgCl2, AgNO3, N-methylmaleimide and p-chloromercuribenzo ic acid (pCMB), agents which target protein thiols. Glutathione, HgCl2 , AgNO3 and pCMB inhibited the peak conductance of I-K(M) without shif ting the half activating voltage (V-1/2), which was comparable to the acetylcholine (ACh)-induced response. The voltage dependence of time c onstants for I-K(M) deactivation in sulfhydryl reagent-, ACh- and non- treated cells resembled, but differed from that in Ba2+-treated cells. These results reveal that there is an accessible cysteine moiety, but not a disulfide bond, either on the M channel protein itself or on a protein directly involved in agonist-M channel coupling. (C) 1997 Else vier Science Ireland Ltd.