ABSTRACT
Invertebrate photoreceptor electrophysiology has mainly been studied with intracellular microelectrodes. Single-channel recording has proved to be difficult, possibly because of unusual plasma membrane configurations; in Limulus polyphemus successful gigaohm seals were obtained only after pronase treatment and brief sonication (Bacigalupo and Lisman, 1983). Here we describe an isolated Hermissenda eye preparation that permits single-channel recording (Hamill et al. 1981) from identified type B photoreceptors; this photoreceptor sub-type has been assiduously studied with intracellular microelectrodes, under both current-clamp and voltage-clamp conditions. Associative conditioning of Hermissenda crassicornis (in the paired fight and rotation paradigm) is attributable in part to the reduction of potassium conductances in the type B photoreceptors (Alkon, 1984, 1987; Alkon et al. 1985). We have used the isolated eye preparation to characterize two types of potassium channels in photoreceptor plasma membranes.
