The Journal of Neurophysiology Vol. 78 No. 6 December 1997, pp. 3019-3027
Copyright ©1997 The American Physiological Society

Heterogeneous Voltage Dependence of Inward Rectifier Currents in Spiral Ganglion Neurons

Zun-Li Mo and Robin L. Davis

Department Biological Sciences, Rutgers University, Piscataway, New Jersey 08855-1059

Mo, Zun-Li and Robin L. Davis. Heterogeneous voltage dependence of inward rectifier currents in spiral ganglion neurons. J. Neurophysiol. 78: 3019-3027, 1997. Inward rectification was characterized in neonatal spiral ganglion neurons maintained in tissue culture. Whole cell current and voltage-clamp techniques were used to show that the hyperpolarization-activated cationic (I_h) current underlies most or all of the inward rectification demonstrated in these neurons. The average reversal potential (41.3 mV) and cesium sensitivity were typical of that found in other neurons and cell types. What was unique about the hyperpolarization-activated currents, however, was that the half-maximal voltages (V_1/2) and slope factors (k) that characterized I_h current activation were graded from neuron to neuron. Voltage-clamp recordings made with standard bath and pipette solutions revealed V_1/2 values that ranged from 78.1 to 122.1 mV, with slope factors from 7.6 to 13.1. These gradations in the voltage-dependent features of the I_h current did not result from variability in the recording conditions because independently measured Na⁺ current-to-voltage relationships were found to be uniform (peak current at 20 mV). Moreover, the range and average V_1/2 and slope values could be altered with activators [8-(4-chlorophenylthio) adenosine 3,5-cyclic monophosphate in combination with okadaic acid] or inhibitors {N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide}of protein indicating that I_h current heterogeneity most likely resulted from differential phosphorylation.

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