L-type calcium channels mediate transmitter release in isolated, wide-field retinal amacrine cells.
Transmitter release in neurons is triggered by intracellular Ca2+ increase via the opening of voltage-gated Ca2+ channels. Here we investigated the voltage-gated Ca2+ channels in wide-field amacrine cells (WFACs) isolated from the white-bass retina that are functionally coupled to transmitter release. We monitored transmitter release through the measurement of the membrane capacitance (Cm). We found that 500-ms long depolarizations of WFACs from -70 mV to 0 mV elicited about a 6% transient increase in the Cm or membrane surface area. This Cm jump could be eliminated either by intracellular perfusion with 10 mM BAPTA or by extracellular application of 4 mM cobalt. WFACs possess N-type and L-type voltage-gated Ca2+ channels. Depolarization-evoked Cm increases were unaffected by the specific N-type channel blocker omega-conotoxin GVIA, but they were markedly reduced by the L-type blocker diltiazem, suggesting a role for the L-type channel in synaptic transmission. Further supporting this notion, in WFACs the synaptic protein syntaxin always colocalized with the pore-forming subunit of the retinal specific L-type channels (Cav1.4 or alpha1F), but never with that of the N-type channels (Cav2.2 or alpha1B ).
Vigh
Jozsef
J
Department of Ophthalmology and Visual Sciences, John Moran Eye Center, University of Utah, Health Sciences Center, Salt Lake City 84132, USA.
Lasater
Eric M
EM
D025042:Amacrine Cells / Q000378:metabolism*; D000818:Animals; D001492:Bass; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology*; D003623:Dark Adaptation; D004594:Electrophysiology; D019084:Fluorescent Antibody Technique, Indirect; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D018408:Patch-Clamp Techniques; D050765:Qa-SNARE Proteins; D009435:Synaptic Transmission / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D005680:gamma-Aminobutyric Acid; D002118:Calcium