Light-dependent repetitive Ca2+ spikes induced by extracellular application of neomycin in honeybee drone photoreceptors.
Photoreceptor cells of the honeybee drone fire, in the presence of the polycationic aminoglycoside neomycin, repetitive slow spike-like potentials superimposed on the receptor potential plateau phase. We have used conventional intracellular recordings and microfluorometric intracellular Ca2+ measurements to characterize these spike potentials. We have shown that the spike frequency increases in a light-intensity-dependent manner. The spikes are fired only when light stimuli depolarize the cell from a resting potential of -50 to -60 mV to at least -40 to -45 mV; they are tetrodotoxin insensitive and blocked by the Ca2+ channel blockers Ni2+, Cd2+, omega-agatoxin TK, verapamil and methoxyverapamil. Depolarization of the photoreceptors with high extracellular K+ in the presence of neomycin in darkness does not generate spikes. Small intracellular Ca2+ oscillations superimposed on the plateau phase of the light-induced increase in intracellular free Ca2+ concentration have a similar temporal pattern as the spike-like potentials. We conclude that the spike-like potentials require stimulation by light and are generated by voltage-dependent Ca2+ channels localized on the soma of the photoreceptors, distal to the basal lamina.
Walz
B
B
Institut für Zoophysiologie und Zellbiologie, Universität Potsdam, Germany.
Zimmermann
B
B
Ukhanov
K
K
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001516:Bees / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000378:metabolism; D005110:Extracellular Space; D008027:Light; D009355:Neomycin / Q000494:pharmacology*; D010786:Photoreceptor Cells / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*
D000900:Anti-Bacterial Agents; D015220:Calcium Channels; D009355:Neomycin; D002118:Calcium