The dihydropyridine isradipine inhibits the murine but not the bovine A-wave response of the electroretinogram.

PURPOSE

In order to record light-evoked responses from photoreceptor cells and the higher neuronal retinal network, the isolated vertebrate retina represents a sensitive tool for basic research of retinal function and for testing the toxicity of ocular therapeutics. In the past, this in vitro technique was optimized for frog and bovine retina; it should be transferred now to the isolated murine retina because the model could allow for functional testing of genes involved in retinal signalling using wild-type and gene-inactivated mice. Thus, alterations in the electroretinogram (ERG) may reveal differences in retinal information processing because of the inactivation of a specific gene.

METHODS

We used a superfused vertebrate retina assay to test bovine and murine retina.

RESULTS

In order to evaluate the sensitivity of the ERG recording technique from the isolated murine retina, we first determined the light intensity response and the stability of the a-wave amplitude during ERG recording, which did not differ between the species. However, testing the dihydropyridine sensitivity of the a-wave, we found that the murine a-wave was highly sensitive towards racemic isradipine (8-25 nM) but the bovine retina a-wave was not. A similar species-dependent difference was observed for mibefradil (10 muM).

CONCLUSION

Murine and bovine retina differ with respect to transretinal signalling. At the level of photoreceptor cells, the ERG/a-wave is modulated by isradipine-sensitive voltage-gated Ca(2+) channels, which trigger feedback signalling to photoreceptors.