A Ni(2+)-sensitive component of the ERG b-wave from the isolated bovine retina is related to E-type voltage-gated Ca(2+) channels.
BACKGROUND
Voltage-dependent Ca(2+) channels trigger and control important cellular processes like neurotransmitter release and secretion, long-term potentiation, and gene expression in excitable cells. During retinal signal perception and processing, presynaptic Ca(2+) channels facilitate neurotransmitter release in photoreceptors and bipolar neurons, at nonspiking synapses which generate graded potentials.


METHODS
The nature of voltage-gated Ca(2+) channels involved in retinal signal transduction is investigated in the present report by recording the electroretinogram (ERG) from the isolated and perfused bovine retina. Transcripts of the E/R- and T-type Ca(2+) channels are detected by RT-PCR.


RESULTS
Using the Ca(2+) channel antagonists (+/-)-isradipine, NiCl(2), mibefradil, and SNX-482 results in either stimulatory or inhibitory effects on the ERG b-wave amplitude. On the transcript level, mRNA is detected for the E/R-type and a T-type voltage-gated Ca(2+) channel containing Ca(v)2.3 and Ca(v)3.1 as ion-conducting subunits, respectively.


CONCLUSIONS
Blocking of the E/R-type Ca(2+) channels by NiCl(2) (10 microM) and SNX-482 (30 nM) contributes to the stimulatory effect, whereas antagonism of T-type as well as L-type Ca(2+) channels meditates the inhibitory action on the b-wave amplitude. Thus, a novel function for E/R-type voltage-gated Ca(2+) channels is probably associated with the visual signal transduction in the mammalian retina.
Lüke
Matthias
M
Institute of Neurophysiology, University of Cologne, Robert-Koch Str. 39, 50931 Cologne, Germany.
Henry
Margit
M
Lingohr
Thea
T
Maghsoodian
Mehran
M
Hescheler
Jürgen
J
Weiergräber
Marco
M
Sickel
Werner
W
Schneider
Toni
T
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D020908:Calcium Channels, R-Type / Q000502:physiology; D020747:Calcium Channels, T-Type / Q000502:physiology; D002417:Cattle; D003623:Dark Adaptation; D004596:Electroretinography / Q000187:drug effects*; D009532:Nickel / Q000494:pharmacology*; D010775:Photic Stimulation; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000187:drug effects* / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014785:Vision, Ocular / Q000502:physiology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020908:Calcium Channels, R-Type; D020747:Calcium Channels, T-Type; D012333:RNA, Messenger; C022838:nickel chloride; D009532:Nickel