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1The effects of l-oleoyl-2-acetyl-sn-glycerol (OAG), phorbol 12-myristate 13-acetate (PMA), 4--phorbol and muscarine on B-neurones from bull-frog sympathetic ganglion were studied by means of whole-cell patch-clamp recording. With the exception of 4-x-phorbol, all of these agonists reduced the steady-state outward current recorded at -30 mV as a result of suppression of a voltage-dependent, non-inactivating K+-current, the M-current, (IM).2 Of the cells tested, 34% displayed bona fide responses to OAG (20 fLM). The chance of recording a response was not decreased when the protein kinase inhibitor, l-(5-isoquinolinylsulphonyl)-2-methylpiperazine (H-7; 50 or 75 tLM) was included simultaneously in the extracellular solution and in the pipette solution. 3 The presence of 50 pM H-7 on both sides of the membrane or 500 nM staurosporine in the pipette solution did not prevent responses to brief (1-2 min) or prolonged (>20 min) applications of PMA.4 Brief (1-2min) extracellular application of H-7 (300t9M) suppressed IM by about 29%.5 The most likely explanation of these data is that PMA and OAG modulate IM via a mechanism that is independent of protein kinase C (PKC). The availability of such a mechanism poses new questions as to the mechanism of muscarine-induced IM suppression.

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