INHIBITION OF PHOSPHOLIPASE-C BY U-73122 BLOCKS ONE-COMPONENT OF THE RECEPTOR CURRENT IN LIMULUS PHOTORECEPTOR

the ventral nerve photoreceptor of Limulus a short, intense flash evok es a receptor current consisting of three components. In contrast to o ther hypotheses, we suggested previously that only the second componen t of the current is activated by the phospholipase C pathway, which re leases calcium from intracellular stores by inositol trisphosphate. Th e present paper gives further evidence to our suggestion. It is demons trated that U-73122, a specific inhibitor for the phospholipase C, sel ectively blocks the second component. The first and third components a re moderately affected and could still be activated after the complete block of the second one. Results support the idea that the first and third components are activated by pathways operating independently of phospholipase C.