T-type Ca(2+) channels mediate neurotransmitter release in retinal bipolar cells.
Transmitter release in neurons is thought to be mediated exclusively by high-voltage-activated (HVA) Ca(2+) channels. However, we now report that, in retinal bipolar cells, low-voltage-activated (LVA) Ca(2+) channels also mediate neurotransmitter release. Bipolar cells are specialized neurons that release neurotransmitter in response to graded depolarizations. Here we show that these cells express T-type Ca(2+) channel subunits and functional LVA Ca(2+) currents sensitive to mibefradil. Activation of these currents results in Ca(2+) influx into presynaptic terminals and exocytosis, which we detected as a capacitance increase in isolated terminals and the appearance of reciprocal currents in retinal slices. The involvement of T-type Ca(2+) channels in bipolar cell transmitter release may contribute to retinal information processing.
Pan
Z H
ZH
Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, MI 48201, USA. zhpan@med.wayne.edu
Hu
H J
HJ
Perring
P
P
Andrade
R
R
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020747:Calcium Channels, T-Type / Q000235:genetics / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D025802:Electric Capacitance; D005089:Exocytosis / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D020748:Mibefradil / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009553:Nimodipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D020318:Rats, Long-Evans; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D002614:Chelating Agents; D018377:Neurotransmitter Agents; D012333:RNA, Messenger; D020748:Mibefradil; D003035:Cobalt; D004533:Egtazic Acid; D009553:Nimodipine; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium