Article
Two Ni2+-sensitive components of the ERG-b-wave from the isolated bovine retina are related to R- and T-type voltage-gated Ca2+-channels
Search Medline for
Authors
Published: | September 22, 2004 |
---|
Outline
Text
Objective
Neuronal voltage-gated Ca2+ channels trigger transmitter release, secretion, synaptic plasticity, and gene expression. During retinal signal transduction, they regulate the spreading of excitation across the retina. From the ten voltage-gated Ca2+-channels identified so far, those were investigated which cannot be easily blocked pharmacologically as the R- and T-type Ca2+ channels.
Methods
Isolated bovine retinae were mounted in a temperature-controlled recording chamber and perfused with an oxygen-saturated standard solution. Electric field potentials were recorded using Ag/AgCl-electrodes, to obtain a complete ERG after each flash of light. After reaching a stable b-wave amplitude, the antagonists were added during a 60 to 75 min long perfusion. Thereupon, the blocker was washed out during 60 - 120 min reperfusion with the standard solution. The changes of a- and b-wave amplitude were calculated and plotted.
Results
NiCl2 (10-100μM) and mibefradil (0.3 - 10μM) do not influence the amplitude of the a-wave. But 100μM NiCl2 blocks the b-wave amplitude completely which is only partially reversible. Ten μM NiCl2 stimulates the b-wave amplitude by 1.3-fold. At lower mibefradil concentrations (0.3 - 1μM), no significant stimulation of b-wave amplitude was observed. The cDNA-fragments of Cav2.3 (R-type) and Cav3.1 (T-type) can be amplified from reverse transcribed total RNA of isolated bovine retina but no transcript of Cav3.2, the most Ni2+-sensitive T-type channel, was detected although we used bovine-specific primer pairs.
Conclusions
The biphasic responses caused by NiCl2 and the inhibition of b-wave by mibefradil reveal to us that besides the well known L-type Ca2+ channels also Ni2+-sensitive Ca2+ channels contribute to the signal transduction in bovine retina, assuming that R-type channels trigger the release of inhibitory and T-type channels trigger the release of excitatory transmitters.