Voltage-dependent Na(+) currents in mammalian retinal cone bipolar cells

J Neurophysiol. 2000 Nov;84(5):2564-71. doi: 10.1152/jn.2000.84.5.2564.

Abstract

Voltage-dependent Na(+) channels are usually expressed in neurons that use spikes as a means of signal coding. Retinal bipolar cells are commonly thought to be nonspiking neurons, a category of neurons in the CNS that uses graded potential for signal transmission. Here we report for the first time voltage-dependent Na(+) currents in acutely isolated mammalian retinal bipolar cells with whole cell patch-clamp recordings. Na(+) currents were observed in approximately 45% of recorded cone bipolar cells but not in rod bipolar cells. Both ON and OFF cone bipolar cells were found to express Na(+) channels. The Na(+) currents were activated at membrane potentials around -50 to -40 mV and reached their peak around -20 to 0 mV. The half-maximal activation and steady-state inactivation potentials were -24.7 and -68.0 mV, respectively. The time course of recovery from inactivation could be fitted by two time constants of 6.2 and 81 ms. The amplitude of the Na(+) currents ranged from a few to >300 pA with the current density in some cells close or comparable to that of retinal third neurons. In current-clamp recordings, Na(+)-dependent action potentials were evoked in Na(+)-current-bearing bipolar cells by current injections. These findings raise the possibility that voltage-dependent Na(+) currents may play a role in bipolar cell function.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 4-Aminopyridine / pharmacology
  • Animals
  • Bicuculline / pharmacology
  • Calcium / pharmacokinetics
  • Cobalt / pharmacology
  • Excitatory Amino Acid Agonists / pharmacology
  • GABA Antagonists / pharmacology
  • Kainic Acid / pharmacology
  • Mammals
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Patch-Clamp Techniques
  • Rats
  • Rats, Long-Evans
  • Receptors, GABA / physiology*
  • Retina / cytology*
  • Retina / physiology
  • Retinal Cone Photoreceptor Cells / physiology*
  • Sodium / metabolism*
  • Sodium Channels / physiology*
  • Tetrodotoxin / pharmacology
  • Visual Pathways
  • gamma-Aminobutyric Acid / pharmacology

Substances

  • Excitatory Amino Acid Agonists
  • GABA Antagonists
  • GABA-C receptor
  • Receptors, GABA
  • Sodium Channels
  • Cobalt
  • Tetrodotoxin
  • gamma-Aminobutyric Acid
  • Sodium
  • 4-Aminopyridine
  • Kainic Acid
  • Calcium
  • Bicuculline