A Ni2+-sensitive component of the ERG-b-wave from the
isolated bovine retina is related to E-type voltage-gated Ca2+
channels (Lüke et al., 2005)
Voltage-dependent
Ca2+ 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 Ca2+ channels facilitate neurotransmitter release in photoreceptors
and bipolar neurons, at non-spiking synapses which generate graded potentials.
The nature of voltage-gated Ca2+ 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 Ca2+ channels are detected by RT-PCR.
Using the Ca2+ channel antagonists (+/-)-isradipine, NiCl2, 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 Ca2+ channel containing Cav2.3 and Cav3.1 as ion conducting
subunits, respectively.
Blocking of the E/R-type Ca2+ channels by NiCl2 (10 µM) and SNX-482 (30 nM)
contributes to the stimulatory effect whereas antagonism of T-type as well as
L-type Ca2+ channels meditates the inhibitory action on the b-wave amplitude.
Thus, a novel function for E/R-type voltage-gated Ca2+ channels is probably
associated with the visual signal transduction in the mammalian retina.