Heterogeneous Voltage Dependence of Inward Rectifier Currents in Spiral Ganglion Neurons

Abstract

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.