Intracellular responses of the Müller (glial) cells of mudpuppy retina: their relation to b-wave of the electroretinogram.

THE EI,ECTROKETI~‘~'~GRAM (ERG) was first recorded by Holmgren in 1865 (ZO), and it has proved to be a useful tool for studying retinal function for almost a century. Despite extensive studies, however, the cellular origins of the ERG components proximal to the receptors remain to be established. Quite recently it has become possible to record intracellularly from the retinal cells with fine micropipettes (2, 22, 34, 39), and thus the precise origins of the ERG components can now be investigated more directly. Our views on the components of the ERG are based mainly on the classic studies of Granit (19, 20). He analyzed the waveforms of the ERG into three components: an initial negative wave (PIII), which lasts the duration of the stimulus; an early transient positive wave (PII); and a late transient positive wave (PI). Granit (19) named these components in order of their sensitivity to ether narcosis. These components interact to produce the a, b, and c waves, respectively, of the intact ERG (16). PI (the c-wave) appears to originate in the pigment epithelium. Noel1 has shown that sodium iodate selectively abolishes the cwave as it destroys the pigment epithelial cells (27, 28). Also, Brown and Diesel (10) have reported intracellular records obtained from pigment epithelial cells and these records show a c-wave of reversed (negative) polarity with respect to the extracellular c-wave. Although the available evidence indicates the pigment epithelium as the probable c-wave generator, < the functional sig-