A voltage-dependent transient K+ current in rat dental pulp cells

We characterized a voltage-dependent transient K+ current in dental pulp fi broblasts on dental pulp slice preparations by using a nystatin perforated- patch recording configuration. The mean resting membrane potential of denta l pulp fibroblasts was -53mV, Depolarizing voltage steps to +60 mV from a h olding potential of -80 mV evoked transient outward currents that are activ ated rapidly and subsequently inactivated during pulses, The activation thr eshold of the transient outward current was -40 mV, The reversal potential of the current closely followed the K+ equilibrium potential, indicating th at the current was selective for K+, The steady-state inactivation of the p eak outward K+ currents described by a Boltzmann function with half-inactiv ation occurred at -47mV, The K+ current exhibited rapid activation, and the time to peak amplitude of the current was dependent on the membrane potent ials. The inactivation process of the current was well fitted with a single exponential function, and the current exhibited slow inactivating kinetics (the time constants of decay ranged from 353ms at -20mV to 217 ms at +60 m V), The K+ current was sensitive to intracellular Cs+ and to extracellular 4-aminopyridine in a concentration-dependent manner, but it was not sensiti ve to tetraethylammonium, mast cell degranulating peptide, and dendrotoxin- I. The blood depressing substance-I failed to block the K+ current. These r esults indicated that dental pulp fibroblasts expressed a slow-inactivating transient K+ current.