Voltage-gated sodium currents in isolated retinal ganglion cells of the cat: relation between the inactivation kinetics and the cell type.
Ganglion cells in the cat retina were retrogradely labeled by injecting a fluorescent dye (DiI) into either the lateral geniculate nucleus (LGN) or the superior colliculus (SC). Cells were then dissociated enzymatically from the retinal tissue. LGN-projecting ganglion cells consisted of 2 different populations, one with small and the other with large somata, which were identified as W and X cells, respectively. SC-projecting cells consisted of a single group of cells with small somata, identified as W cells. The voltage-gated sodium current (INa) was recorded from isolated ganglion cells under the voltage-clamp condition using a patch pipette in the whole cell configuration. INa was identified by reversible tetrodotoxin block. INa was activated by depolarization of the cell from the holding potential (Vh) of -95 mV to membrane voltages (Vm) more positive than -45 mV. The maximum INa was recorded at around -15 mV. INa flowed outward at Vm more positive than +65 mV. The reversal potential of INa became more negative voltages with low extracellular Na concentration ([Na+]o) with a relation of 58 mV for a 10-fold change in [Na+]o. INa was inactivated with a few milliseconds. Once inactivated, INa recovered by holding the cell membrane hyperpolarized. While the voltage dependence of INa activation and steady-state inactivation were constant from cell to cell, the time course of recovery was not. Cells with a large soma showed a rapid recovery, while cells with a small soma showed slow recovery. Thus, the rate of recovery is faster for X cells than for W cells. Perhaps this helps to explain the 'sluggish' firing of the latter cell type.
Kaneda
M
M
National Institute for Physiological Sciences, Okazaki, Japan.
Kaneko
A
A
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002232:Carbocyanines; D002415:Cats; D005829:Geniculate Bodies / Q000166:cytology / Q000502:physiology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D012165:Retinal Ganglion Cells / Q000502:physiology* / Q000648:ultrastructure; D015222:Sodium Channels / Q000502:physiology*; D013477:Superior Colliculi / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D002232:Carbocyanines; D015222:Sodium Channels; C024286:3,3'-dioctadecylindocarbocyanine; D013779:Tetrodotoxin