A voltage‐clamp analysis of inward (anomalous) rectification in mouse spinal sensory ganglion neurones.

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Abstract
Mouse embryo dorsal root ganglion neurons were grown in tissue culture and voltage-clamped with 2 micro-electrodes. Hyperpolarizing voltage commands from holding potentials of -50 to -60 mV evoked slow inward current [Ih] relaxations which were followed by inward tail currents on repolarization to the holding potential. These relaxations are due to the presence of a time- and voltage-dependent conductance provisionally termed Gh. Gh activities over the membrane potential range -60 to -120 mV. The presence of Gh causes time-dependent rectification in the current-voltage relationship measured between -60 and -120 mV. Gh does not inactivate within this range and thus generates a steady inward current at hyperpolarized membrane potentials. The current carried by Gh increases when the extracellular K+ concentration is raised, and is greatly reduced in Na+-free solutions. Current-voltage plots show considerably less inward rectification in Na+-free solution: inward rectification is markedly enhanced when the extracellular K+ concentration is raised. The reversal potential of Ih is close to -30 mV in media of physiological composition. Tail-current measurements suggests that Ih is a mixed Na+-K+ current. Low concentrations of Cs+ relationship block Ih and produce outward rectification in the steady-state current-voltage relationship recorded between membrane potentials of -60 and -120 mV. Cs+ also reversibly abolishes the sag and depolarizing overshoot that distort hyperpolarizing electronic potentials recorded in current-clamp experiments. Impermeant anion substitutes reversibly block Ih; this block is different from that produced by Cs+ or Na+-free solutions: Cs+ produces outward rectification in the steady-state current-voltage relationship recorded over the Ih activation range; in Na+-free solutions inward rectification, of reduced amplitude, can still be recorded since Ih is a mixed Na+-K+-current: in anion-substituted solutios the current-voltage relationship becomes approximately linear. In dorsal root ganglion neurons, anomalous rectification is generated by the time- and voltage-dependent current Ih. The possible function of Ih in sensory neurons is discussed.