CONTRIBUTION OF A NONINACTIVATING POTASSIUM CURRENT TO THE RESTING MEMBRANE-POTENTIAL OF FUSION-COMPETENT HUMAN MYOBLASTS

1. Using the patch-clamp technique, a new non-inactivating voltage-gat ed potassium current, I-K(ni) was studied in cultured fusion-competent human myoblasts. 2. I-K(ni) is activated at voltages above -50 mV and its conductance reaches its maximum around +50 mV. Once activated, th e current remains at a steady level for minutes. 3. Reversal potential measurements at various extracellular potassium concentrations indica te that potassium ions are the major charge carriers of I-K(ni). 4. I- K(ni) is insensitive to potassium channel blockers such as charybdotox in, dendrotoxins, mast cell degranulating (MCD) peptide, 4-aminopyridi ne (4-AP), 3,4-diaminopyridine (3,4-DAP) and apamin, but can be blocke d by high concentrations of TEA and by Ba2+. 5. A potassium channel of small conductance (8.4 pS at +40 mV) with potential dependence and ph armacological properties corresponding to those of I-K(ni) in whole-ce ll recording is described. 6. I-K(ni) participates in the control of t he resting potential of fusion-competent myoblasts, suggesting that it may play a key role in the process of myoblast fusion.