A patch-clamp analysis of spiking properties in cat alpha and beta ganglion cells in retinal wholemounts

Purpose. To assess the intrinsic membrane properties of ganglion cells in relation to the two major morphological classes in the cat's retina ; alpha and beta. Methods. The perforated-patch variation of the patch-clamp technique was used to obtain current-clamp recordings from 79 postnatal RGCs in retinal wholemounts. The fluorescent probe Lucifer Yellow was incorporated into the electrode to anatomically identify the cells from which recordings were made. The wholemount was continually perfused with oxygenated EMEM at 35°C. Results. Successful recordings were obtained from 19 alpha and 60 beta cells. The average resting membrane potential, which did not vary appreciably with cell class or somal size, was -53 8 and in all cases regenerative firing was observed at this potential The input resistances and membrane time constants were not significantly (p<0.05) different between the two classes having values ranging from 200-600 MΩ and 22-30 msecs, respectively. No significant differences (p>0.05) were observed in the half-spike width, which had mean values of 1.7±0 7 and 1.6±0.7 msecs in alpha and beta cells, respectively In response to constant current depolarizations both classes responded with maintained discharges and the number of spikes elicited increased linearly with the magnitude of the injected current. Furthermore, the maximum firing rate obtained in response to maintained depolarizations was significantly higher (1.7 times; p<0.01) in beta cells than in alpha cells. Conclusions. The results provide evidence that the excitable membrane properties underlying spike generation and spiking patterns are qualitatively similar in alpha and beta cells.