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Depletion of calcium stores regulates calcium influx and signal transmission in rod photoreceptors
Author(s) -
Szikra Tamas,
Cusato Karen,
Thoreson Wallace B.,
Barabas Peter,
Bartoletti Theodore M.,
Krizaj David
Publication year - 2008
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2008.160051
Subject(s) - ribbon synapse , microbiology and biotechnology , neurotransmission , cytosol , calcium , chemistry , exocytosis , biophysics , calcium signaling , orai1 , voltage dependent calcium channel , synapse , intracellular , biology , synaptic vesicle , neuroscience , biochemistry , receptor , vesicle , membrane , organic chemistry , enzyme
Tonic synapses are specialized for sustained calcium entry and transmitter release, allowing them to operate in a graded fashion over a wide dynamic range. We identified a novel plasma membrane calcium entry mechanism that extends the range of rod photoreceptor signalling into light‐adapted conditions. The mechanism, which shares molecular and physiological characteristics with store‐operated calcium entry (SOCE), is required to maintain baseline [Ca 2+ ] i in rod inner segments and synaptic terminals. Sustained Ca 2+ entry into rod cytosol is augmented by store depletion, blocked by La 3+ and Gd 3+ and suppressed by organic antagonists MRS‐1845 and SKF‐96365. Store depletion and the subsequent Ca 2+ influx directly stimulated exocytosis in terminals of light‐adapted rods loaded with the activity‐dependent dye FM1–43. Moreover, SOCE blockers suppressed rod‐mediated synaptic inputs to horizontal cells without affecting presynaptic voltage‐operated Ca 2+ entry. Silencing of TRPC1 expression with small interference RNA disrupted SOCE in rods, but had no effect on cone Ca 2+ signalling. Rods were immunopositive for TRPC1 whereas cone inner segments immunostained with TRPC6 channel antibodies. Thus, SOCE modulates Ca 2+ homeostasis and light‐evoked neurotransmission at the rod photoreceptor synapse mediated by TRPC1.