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

W. Rowland Taylor, Catherine Morgans

Research output: Contribution to journalArticle

95 Scopus citations

Abstract

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 GΩ 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°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 α-ID. 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.

Original languageEnglish (US)
Pages (from-to)541-552
Number of pages12
JournalVisual neuroscience
Volume15
Issue number3
DOIs
StatePublished - May 1 1998

Keywords

  • Calcium channels
  • Calcium-dependent chloride current
  • Electrotonic properties
  • Mammalian photoreceptor

ASJC Scopus subject areas

  • Physiology
  • Sensory Systems

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