A HYPERPOLARIZATION-ACTIVATED CATION CURRENT (I-H) CONTRIBUTES TO RESTING MEMBRANE-POTENTIAL IN RAT SUPERIOR CERVICAL SYMPATHETIC NEURONS

Using perforated-patch voltage-clamp recording, a prominent hyperpolar ization-activated inward cation current (I-h) has been identified in d issociated, cultured and replated, superior cervical sympathetic (SCG) neurones from 17-day-old rats. I-h was identified as a slowly activat ed inward current on hyperpolarizing from -60 mV, with an extrapolated null potential (in 3 mM [K+](out)) of -42 mV, The activation range fo r I-h was -40 to -100 mV, with a half-activation voltage (V-0.5) of -6 3 mV. The current was suppressed by 1 mM Cs+ but not by 1 mM Ba2+. The reversal potential for the current change induced by Cs+ agreed with the null potential for I-h.I-h conferred strong inward rectification t o the current-voltage curve negative to -55 mV in both voltage-clamp a nd current-clamp recording. This inward rectification was reduced by 1 mM Cs+. In a sample of eight cells with initial resting membrane pote ntials between -51 and -64 mV, Cs+ increased the resting potential of all cells by between 2.5 and 21 mV. These results indicate that I-h co ntributes a tonic inward (depolarizing) component to the maintenance o f the resting membrane potential in SCG neurones.