Abstract
Horizontal cells (HCs) have larger receptive field than the dendritic field, due to gap junctional coupling between the same type of cells forming a syncytium. The receptive field profile of the cells is described by an exponential decline of light response amplitude as a function of distance from a recording electrode when a slit of light is used, the space constant of this exponential decay being proportional to (gs/gm)1/2 (where gs: gap junctional conductance, gm: plasma membrane conductance). Effects of pH on H1 type HCs in isolated carp retinae were examined in order to investigate its suppression of transmitter release of glutamate and gap junctions of this syncytium. Acidification of Ringer's solution containing 10 mM HEPES from pH 7.6 to 7.3 hyperpolarised its resting membrane potential, decreased dye diffusion of intracellularly-injected Lucifer Yellow to adjacent cells, and increased the space constant of the receptive field. Effects of alkalinisation of Ringer from pH 7.6 to 7.9 were opposite. These results indicated that the acidification induces a larger decrease in gm than in gs. This suggests that higher concentration of proton in the Ringer would strongly suppress the transmitter release of glutamate from cones to HCs via Ca-channels at the cone terminals much more than the gap junctional channels of H1 HCs. [Jpn J Physiol 54 Suppl:S164 (2004)]
