Actions of neomycin on electrical light responses, Ca2+ release, and intracellular Ca2+ changes in photoreceptors of the honeybee drone

Neomycin, known to inhibit phospholipase C-mediated IP3 formation, was appl ied in the bath or injected into cells and its effects on electrical light responses were analyzed. Neomycin effects on inositol 1,4,5-trisphosphate- and Ca2+-induced Ca2+ release from the endoplasmic reticulum and/or the lig ht-induced Ca2+ elevation were also studied. Neomycin (0.5 mmol l(-1)) bloc ked inositol 1,4,5-trisphosphate-. caffeine-, and Ca2+-induced Ca2+ release . Bath application of neomycin decreased the sensitivity to 20-ms light fla shes by a factor of up to 100 and slowed the kinetics of dim flush response s. Intracellularly injected neomycin desensitized the photoreceptors more t han 1 log unit, increased the latency, and slowed the rate of rise of the l ight response Neomycin (0.5 mmol l(-1)) in the bath delayed and reduced the transient component of responses to 1-s steps of light at intel mediate in tensities. It also decreased and slowed the light-induced, and it blocked t he caffeine-induced intracellular Ca2+ elevation. The combined pharmacologi cal effects of neomycin are suggested to decrease the Ca2+-mediated amplifi cation of the phototransduction cascade and the Ca2+-mediated acceleration of processes determining the kinetics of light responses.