Abstract
Intense illumination of long duration induced a large transient increase in extracellular calcium (Δ[Ca 2+] o) and potassium (Δ[K +] o) during and after light in bee retina when measured with ion-selective microelectrodes. Whenever a large Δ[Ca 2+] o appeared, it was accompanied by a transient afterdepolarization (TA). Both the increase in [Ca 2+] o, [K +] o and the TA were reduced or abolished when sodium was replaced by arginine, choline or lithium (Li +) ions. At 0-Na conditions a Na independent decrease in [Ca 2+] o was observed during illumination only. A pronounced transient depolarization of the photoreceptor in the dark due to transient anoxia did not result in a significant change in [Ca 2+] o. In some retinae the elevated level of [K +] o after light was absent, however a small Na-dependent TA was still observed. The above findings suggest that intense long illumination induces a large Ca 2+ influx into the photoreceptors which is followed by Na-dependent Ca 2+ efflux due to Na-Ca exchange. The light-induced afterdepolarization arises mainly from K + accumulation in the extracellular space but partially from the electrogenicity of Na-Ca exchange.
Published Version
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