PHARMACOLOGY OF A CLONED POTASSIUM CHANNEL FROM MOUSE-BRAIN (MK-1) EXPRESSED IN CHO CELLS - EFFECTS OF BLOCKERS AND AN INACTIVATION PEPTIDE

1 Chinese hamster ovary cells (CHO), maintained in cell culture, were stably transfected with DNA for the MK-1 voltage-activated potassium channel, previously cloned from a mouse brain library. 2 Voltage-activated currents were recorded by the whole-cell patch clamp method. In CHO cells transfected with the vector only, there were no significant outward voltage activated currents. However, large outward voltage-activated potassium currents were always observed in those cells which had been transfected with the vector containing the DNA encoding for MK-1. 3 These potassium currents activated from -40 mV, and reversed at the potassium equilibrium potential. The half-maximal conductance of MK-1 was at -10 mV and had a slope factor of 11 mV when fitted with a Boltzmann function. There was only very slight (< 10%) inactivation of MK-1 even at very large positive voltages. 4 MK-1 was reversibly blocked by: 4-aminopyridine (4-AP, 0.1-4 mM), Toxin I (10-100 nm), mast cell degranulating peptide (1 mum), tetraethylammonium (TEA, 4-10 mM), tedisamil (100 muM), quinine (100 muM) and ciclazindol (100 mum); all applied to the outside of the cell from a 'U tube' rapid perfusion system. 4-AP may block closed as well as open MK-1 potassium channels. 5 A synthetic 20 amino acid peptide derived from the N-terminus sequence of the Shaker B potassium channel (the 'inactivation peptide') produced dramatic inactivation of MK-1 when applied to the inside, but not the outside of the cell. Reducing peptide concentration or 'degrading' the peptide produced less inactivation. 6 The block of MK-I by the synthetic inactivation peptide was quite different in time dependence from block by internal TEA (0.4-4 mm), which probably blocks much more quickly but less potently than the peptide.