High sensitivity to internal tetraethylammonium in K(Ca) channels of cerebrovascular smooth muscle cells.

Patch clamp methods were used to study the properties of calcium-dependent K(Ca) channels in enzyme dissociated smooth muscle cells from the cerebral arteries of adult rats. Dissociated muscle cells were maintained at 4 degrees C for up to 48 h prior to use. Inside-out membrane patches excised from these cells contained a K(Ca) channel with a conductance of 92 +/- 2.6 pS in symmetrical 140 mM potassium solutions. This channel was activated by membrane depolarization and by cytoplasmic calcium, and showed negligible permeability to sodium or cesium ions. Single channel currents were reduced by internal application of tetraethylammonium ions, with a Kd = 0.31 mM.