Mechanisms of pH regulation and the generation of the electroretinogramb-wave in the toad retina

In the work presented in this thesis, several physiological properties of the isolated toad retina, including extracellular pH, light-evoked extracellular K$\sp{+}$ changes, light-evoked responses of rods and Muller cells, and the electroretinogram (ERG), have been studied under various conditions.The present work has identified a pH regulating mechanism in which bicarbonate/CO$\sb2$ serves as the primary buffer system to balance the acid produced by retinal cells, and carbonic anhydrase accelerates the pH regulating process. Since carbonic anhydrase is concentrated primarily in Muller cells, this result points to a critical role for Muller cells in maintaining a proper pH in the retinal microenvironment.The present work has provided strong evidence to support the K$\sp{+}$-Muller cell theory of the generation of the ERG b-wave. Recordings of the distal K$\sp{+}$ increase show that this K$\sp{+}$ increase has all the properties needed to produce the b-wave, including the proper amplitude and time course. In addition, blocking K$\sp{+}$ conductance in the Muller cell with barium inhibits the b-wave and the Muller cell depolarization, but has no significant effect on the distal K$\sp{+}$ increase. These results directly prove that Muller cells play a part in the b-wave generating mechanism, and rule out the possibility that the distal K$\sp{+}$ increase is due to the passive release of K$\sp{+}$ from the Muller cell. These observations, therefore, have confirmed the validity of the K$\sp{+}$-Muller cell theory of the generation of the ERG b-wave.The present work has also shown that microenvironment pH, bicarbonate/CO$\sb2$, and Cl$\sp{-}$ all affect the b-wave by influencing the distal K$\sp{+}$ increase, indicating that ON-bipolar cells are affected by these factors. Detailed studies have provided further evidence that leads to a hypothetical model of how the ON-bipolar cells, whose photoresponse is the key step of the b-wave generation, use Cl$\sp{-}$/HCO$\sb3\sp{-}$ exchange coupled with Na$\sp{+}$/H$\sp{+}$ exchange to maintain their high intracellular Cl$\sp{-}$ concentration needed to produce their normal photoresponses.U of I OnlyETDs are only available to UIUC Users without author permissio