The electroretinogram, standing potential, and light peak of the perfused cat eye during acid-base changes
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Abstract:
DC recordings of light-evoked responses were made in the isolated, arterially perfused cat eye during four acid-base changes designed to alter intracellular pH (pHi) without appreciably altering extracellular pH (pH0). Two acid-base changes were designed to decrease pHi: substitution of high pCO2, high [HCO3-] perfusate for control perfusate and injection of NaHCO3 solution (pH 7.4) into the control perfusate. The initial effects of these two changes were similar: standing potential decreased, the b-wave amplitude decreased, and the c-wave amplitude increased. Subsequent effects, which included rebounds, were complex. The two other acid-base changes were designed to increase pHi: substitution of low pCO2, low [HCO3-] perfusate for the control perfusate and injection of NH4Cl solution into the control perfusate. The initial effects of these two changes were similar; the effects were opposite to those described above for acid-base changes (i) and (ii). The effects of all four acid-base changes were reversible. From these and previously published findings on the effects of pH0, we conclude that during acid-base changes, the initial change in the standing potential varies directly with pHi/pH0, the initial change in b-wave amplitude varies directly with pHi, and the initial change in c-wave amplitude varies inversely with pHi. We also studied the effects of the four acid-base changes on the light peak, a slow voltage response to light generated by the retinal pigment epithelium. Under acid-base changes (i), (ii), and (iii) the light peak was severely depressed. Injection of 2 mM NH4Cl, acid-base change (iv), had little effect on the light peak; however, injection of 5-10 mM NH4Cl did depress the light peak. These results may be interpreted in several ways, for example, the light peak may be sensitive to changes in [HCO-3]0 or to pHi. In any case, we conclude that pH0 is a relatively minor factor influencing the amplitude of the light peak.