Abstract
ON-OFF type transient amacrine cells (TACs) are intensely connected with each other by gap junctions, forming a syncytium with a wide receptive field. We studied effects of external pH (pH0) on the control of cell functions. Photoresponses of TACs in isolated retinae were recorded intracellularly. A slit of light was used as photostimuli, which simplified the estimation of the current flow in the cellular network into a one-dimensional problem. Under slightly alkaline pH0 conditions of the superfusate, by raising only 0.2 pH units from the baseline of 7.60, we found a remarkable increase of the conduction velocity (40%) as well as a reduction of the space constant (15%) of the receptive field, besides depolarization of the resting potential and enhancement of photoresponses. Acidic conditions, by lowering 0.2 pH units, had opposite effects, decreasing the conduction velocity by 20-25%, increasing the space constant (15-20%). Based on our theoretical model, combined with experimental measurements of conduction velocity and space constant, we could estimate both the gap junctional and the non-gap junctional conductances of the cell. Thus, we suggest that protons could contribute to the reduction of conductances, especially at the plasmamembrane but also at gap junctions. [J Physiol Sci. 2008;58 Suppl:S173]
