Comparison of pharmacological agents (aspartate vs. aminophosphonobutyric plus kynurenic acids) to block synaptic transmission from retinal photoreceptors in frog.

The combination of aminophosphonobutyric plus kynurenic acids (APB/Kyn) was compared to aspartate with respect to its ability to block synaptic transmission from photoreceptors. Like aspartate, APB/Kyn blocks photoreceptor synaptic transmission, as monitored by the b- and d-waves of the electroretinogram, by the proximal negative response and M-wave of the proximal retina, and by the light-evoked increase in extracellular K+ concentration in the inner plexiform layer. Unlike aspartate, APB/Kyn has relatively minor effects on retinal resistance, light-evoked changes in K+ and Ca2+ concentrations in the subretinal space, light-evoked changes in subretinal space volume, resting extracellular concentrations of K+ and Ca2+ in the proximal and distal retina, and the c-wave. Effects of APB/Kyn are generally more reversible than effects of Asp. A disadvantage of APB/Kyn is that the a-wave usually becomes smaller and slower. Overall, APB/Kyn disrupts the retina less than aspartate. Therefore, in some situations in which blockade of photoreceptor synaptic transmission is desired, the use of APB/Kyn may be preferable to that of aspartate.