Current components stimulated by different G-proteins in Limulus ventral photoreceptor.

The components of the light-activated current in ventral photoreceptor of Limulus have different physical and pharmacological properties, indicating the operation of different transduction pathways. We investigated whether these pathways are activated by different G-proteins. An antiserum, directed against the C-terminal sequence QLNLKEYNLV of the alpha subunit of the Gq-protein, which is present in squid photoreceptor, was injected into the ventral photoreceptor of Limulus. This Gq-alpha mediates the light-dependent activation of PLC. Injections of the antibody into the photoreceptor blocked the second component of the light-evoked current in Limulus ventral photoreceptor, but the other components could still be activated. The results support our earlier hypothesis that the transduction pathways of the current components are selectively activated by different G-proteins.