THE INFLUENCE OF MGCL2 AND APB ON THE LIGHT-INDUCED POTASSIUM CHANGESAND THE ERG B-WAVE OF THE ISOLATED SUPERFUSED RAT RETINA

The ERG and the extracellular potassium concentration, [K+](0), of the isolated superfused rat retina were measured in a physiological solut ion and in solutions containing 10 mM MgCl2 or 100 mu M APE. MgCl2 nea rly abolished the b-wave, but the light-induced distal [K+](0), increa se was enlarged from 0.13 +/- 0.05 to 0.28 +/- 0.08 mM. There was also an increase in the light-induced [K+](0), in the proximal retina. APE abolished the b-wave completely, and the distal light-induced [K+](0) , increase was then replaced by a [K+](0), decrease, Upon return to th e control solution, there was a larger transitory [K+](0) increase tha n under control conditions, and this occurred before the b-wave had re turned. Under these experimental conditions, the distal [K+](0) increa se could not be correlated with the b-wave, and so the Muller cells ar e unlikely to be the main source of the rising phase of the b-wave, Mo re probable sources of the b-wave are the on-bipolar cells with their metabotropic and ionotropic receptors, with only the latter apparently being blocked by MgCl2.