Localization and properties of voltage-gated calcium channels in cone photoreceptors of Tupaia belangeri

Vis Neurosci. 1998 May-Jun;15(3):541-52. doi: 10.1017/s0952523898153142.


In spiking neurons, phasic, calcium-dependent transmitter release is initiated when a presynaptic action potential activates voltage-dependent calcium channels. Vertebrate photoreceptors are nonspiking neurons that continuously release transmitter. This study uses patch-clamp recording to examine the electrophysiological properties of mammalian cones in intact retina. The cell capacitance was 10+/-1 pF and the input resistance was 0.52+/-0.46 G omega at -65 mV (31 cells). A specific membrane capacitance of 1.2 pF/cm2 was calculated. The cones did not appear to be chemically or electrically coupled. The calcium conductance averaged 3+/-1 nS (five cells). Fifty percent of the calcium channels were active at -40 mV, and at this voltage the number of active channels changed e-fold for a 6-mV voltage change. At 25 degrees C, the current reached a peak within about 1 ms after onset of a step to -35 mV. The calcium influx produced by depolarization activated a chloride conductance with a delay of a few milliseconds. The channels did not completely inactivate during maintained depolarization. The calcium channels were partially blocked by high concentrations of nifedipine, an L-type specific antagonist, and were recognized by an antibody raised against the L-type subunit alpha-1D. The immunohistochemical staining shows that the calcium channels are localized to the synaptic terminals. The immunohistochemical, physiological, and pharmacological properties indicate that the calcium channels in mammalian photoreceptors may represent a novel isoform, possibly with some homologies to the L-type class. The activation range of the channels matches the physiological operating range of photoreceptors.

MeSH terms

  • Animals
  • Calcium / metabolism
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels / drug effects
  • Calcium Channels / metabolism*
  • Chloride Channels / metabolism
  • Chlorides / metabolism
  • Female
  • Fluorescent Antibody Technique, Indirect
  • Male
  • Membrane Potentials / physiology
  • Nifedipine / pharmacology
  • Patch-Clamp Techniques
  • Photoreceptor Cells / metabolism
  • Presynaptic Terminals / metabolism*
  • Retinal Cone Photoreceptor Cells / physiology*
  • Tupaia*


  • Calcium Channel Blockers
  • Calcium Channels
  • Chloride Channels
  • Chlorides
  • Nifedipine
  • Calcium