A VOLTAGE-DEPENDENT AND A VOLTAGE-INDEPENDENT POTASSIUM CHANNEL IN BROWN ADIPOCYTES OF THE RAT

Single-channel recordings of a voltage-dependent potassium channel in brown adipocytes of the rat confirm recordings of macroscopic currents . Single-channel conductance (gamma) is 8 pS at degrees 20C in KF solu tion inside vs. a modified Ringer's solution outside. With KCl solutio n outside, gamma is 17 pS for outward currents and 21 pS for inward cu rrents. The majority of the channels inactivate with a time constant a round 200 ms; deactivation occurs within milliseconds. The channel is blocked by tetraethylammonium (TEA) with an inhibiting constant of 1.8 mM. The type of block is fast. Selectivity sequence for monovalent ca tions is K+ > Rb+ >> NH4+ >> Li+ greater than or equal to Na+ approxim ate to Cs+. Cs+ at the outside causes a voltage-dependent block of inw ard currents. This channel is remarkably similar to the delayed rectif ier of the F-type in the node of Ranvier. Occasionally, an additional K+ channel was found. This channel is voltage-insensitive, not blocked by 10 mM TEA, and has not been recorded in brown adipocytes before. P hysiological relevance of this channel could be the steady-state membr ane potential.