INDUCTION OF PHOTORESPONSE BY THE HYDROLYSIS OF POLYPHOSPHOINOSITIDESIN THE HERMISSENDA TYPE-B PHOTORECEPTOR

Direct evidence that the photoresponse of the Hermissenda type B photo receptor cell is triggered directly by the hydrolysis of phosphatidyli nositol 4,5-bisphosphate (PIP2) was obtained. Neomycin and spermine, w hich inhibit PIP2 breakdown, suppressed light response, while injectio n of inositol 1,4,5-trisphosphate (IP3), guanosine 5'-(3-O-thio)tripho sphate (GTP gamma S), guanosine 5'-(2-O-thio)diphosphate (GDP beta S), cAMP, cGMP did not alter the light-induced Na+ influx underlying the photoresponse. Suppression of the photoresponse was also observed with decrease of total amount of membraneous PIP2 induced by injection of the phosphoinositides (PI) turnover inhibitors, isobutylmethylxanthine (IBMX), LiCl and R 59022. (C) 1994 Academic Press, Inc.