Abstract
Gap junctions are found in neuroepithelial cells in the early embryonic retina (Fujisawa et al., 1976). However, the gap junction disappears as the retinal cells differentiate and the functional role of the gap junction in the early retinal development remains unknown. In the present study, the electrophysiological properties of the retinal neuroepithelial cells were investigated by intracellular recordings in an isolated preparation of the retinal neuroepithelium dissected from embryonic day 3 (E3) chick. The retinal neuroepithelial cells showed resting membrane potentials of -63 to -89 mV. Input resistances were measured by passing steady depolarizing and hyperpolarizing currents of 0.2 nA. The input resistance ranged from 14 to 80 Mohm. No evidence for conventional action potentials was found even with a depolarizing current of 1.0 nA. Carbenoxolone (CBX), a gap junction channel blocker, was applied to the retinal neuroepithelium during the intracellular recording. The input resistance was remarkably increased by the application of CBX; 10 μM of CBX increased the input resistance by 2-4 times and 100 μM of CBX increased it by 5-6 times. The resting membrane potential became unstable and shifted in depolarizing direction with CBX. Alexa Fluor 488 hydrazide (MW: 570.48) was injected into the cell by passing hyperpolarizing current pulses through the recording electrode. The injection of Alexa Fluor 488 revealed clear dye coupling. These results suggest that the gap junctional coupling between the retinal neuroepithelial cells lowers the input resistance and stabilizes the resting membrane potential of the neuroepithelial cell. [J Physiol Sci. 2007;57 Suppl:S110]
