Alteration of sensitivity and time scale in invertebrate photoreceptors exposed to anoxia, dinitrophenol, and carbon dioxide.

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Abstract
The effects of anoxia, 2,4-dinitrophenol (DNP), and carbon dioxide (CO2) on the late receptor potential of Balanus lateral ocelli, Limulus ventral eyes, and the retinular cells of Limulus lateral eyes were studied. Anoxia, DNP or exposure to 100% CO2 caused a depolarization of 5-30 mV and a gradual reduction and eventually abolition of the late receptor potential and an increase in the latency and time to peak of the response. This lengthening of the time scale was in contrast to the response obtained in photoreceptors that have been light-adapted or injected with Ca. In that case a loss in sensitivity was associated with a decrease in latency and time to peak. Because of these observed differences, the effects of metabolic inhibition were not attributed merely to a loss in regulation of intracellular free Ca. Rather, because alteration of intracellular pH (pHi) by using either (NH4)2SO4 or CO2 produced changes in the photoresponse similar to those caused by metabolic inhibition, changes in pHi during metabolic inhibition may have accounted in part for the lengthening of the time scale. In addition to the changes in pHi and internal Ca2+ concentration due to metabolic inhibition, the possible role of other consequences of metabolism in the transduction mechanism was discussed.

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