The influence of MgCl2 and APB on the light-induced potassium changes and the ERG b-wave of the isolated superfused rat retina.
The ERG and the extracellular potassium concentration, [K+]o, of the isolated superfused rat retina were measured in a physiological solution and in solutions containing 10 mM MgCl2 or 100 mu M APB. MgCl2 nearly abolished the b-wave, but the light-induced distal [K+]o increase was enlarged from 0.13 +/- 0.05 to 0.28 +/- 0.08 mM. There was also an increase in the light-induced [K+]o in the proximal retina. APB abolished the b-wave completely, and the distal light-induced [K+]o increase was then replaced by a [K+]o decrease. Upon return to the control solution, there was a larger transitory [K+]o increase than under control conditions, and this occurred before the b-wave had returned. Under these experimental conditions, the distal [K+]o increase could not be correlated with the b-wave, and so the Muller cells are unlikely to be the main source of the rising phase of the b-wave. More 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. The extracellular [K+]o changes, however, had an influence upon the slow potentials of the ERG.
Hanitzsch
R
R
Carl-Ludwig-Institute of Physiology, University Leipzig, Germany.
Lichtenberger
T
T
Mattig
W U
WU
D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004596:Electroretinography / Q000187:drug effects; D066298:In Vitro Techniques; D015636:Magnesium Chloride / Q000494:pharmacology*; D010775:Photic Stimulation; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D012160:Retina / Q000187:drug effects* / Q000502:physiology
D000613:Aminobutyrates; D015636:Magnesium Chloride; C012729:2-amino-4-phosphonobutyric acid; D011188:Potassium