Blockade of amiloride-sensitive sodium channels alters multiple components of the mammalian electroretinogram.

Retinal neurons and Muller cells express amiloride-sensitive Na+ channels (ASSCs). Although all major subunits of these channels are expressed, their physiological role is relatively unknown in this system. In the present study, we used the electroretinogram (ERG) recorded from anesthetized rabbits and isolated rat and rabbit retina preparations to investigate the physiological significance of ASSCs in the retina. Based upon our previous study showing expression of alpha-ENaC and functional amiloride-sensitive currents in rabbit Muller cells, we expected changes in Muller cell components of the ERG. However, we observed changes in other components of the ERG as well. The presence of amiloride elicited changes in all major components of the ERG; the a-wave, b-wave, and d-wave (off response) were enhanced, while there was a reduction in the amplitude of the Muller cell response (slow PIII). These results suggest that ASSCs play an important role in retinal function including neuronal and Muller cell physiology.