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 applied 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 light-induced Ca2+ elevation were also studied. Neomycin (0.5 mmol x l(-1)) blocked inositol 1,4,5-trisphosphate-, caffeine-, and Ca2+-induced Ca2+ release. Bath application of neomycin decreased the sensitivity to 20-ms light flashes by a factor of up to 100 and slowed the kinetics of dim flash responses. Intracellularly injected neomycin desensitized the photoreceptors more than 1 log unit, increased the latency, and slowed the rate of rise of the light response. Neomycin (0.5 mmol x l(-1)) in the bath delayed and reduced the transient component of responses to 1-s steps of light at intermediate intensities. It also decreased and slowed the light-induced, and it blocked the caffeine-induced intracellular Ca2+ elevation. The combined pharmacological effects of neomycin are suggested to decrease the Ca2+-mediated amplification of the phototransduction cascade and the Ca2+-mediated acceleration of processes determining the kinetics of light responses.
Walz
B
B
Institut für Biochemie und Biologie, Tierphysiologie, Potsdam, Germany. walz@rz.uni-potsdam.de
Ukhanov
K
K
Zimmermann
B
B
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D001516:Bees / Q000502:physiology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D008029:Lighting; D009355:Neomycin / Q000494:pharmacology*; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism* / Q000528:radiation effects*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology*
D011500:Protein Synthesis Inhibitors; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D009355:Neomycin; D002118:Calcium