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. 1996 Feb;70(2):924–931. doi: 10.1016/S0006-3495(96)79635-2

The nature of rhodopsin-triggered photocurrents in Chlamydomonas. I. Kinetics and influence of divalent ions.

E M Holland 1, F J Braun 1, C Nonnengässer 1, H Harz 1, P Hegemann 1
PMCID: PMC1224992  PMID: 8789109

Abstract

In the green alga Chlamydomonas chlamyrhodopsin fulfills its role as a light sensor by absorbing light and activating photoreceptor channels within the eyespot area. At intense light stimuli, the photoreceptor (P) current triggers a fast and a slow flagellar current that finally leads to backward swimming (stop response). Here we report about probing the photoreceptor current directly at the eyespot. This allows the detection of the whole P current with a size of above 50 pA. The P current appears with a delay of less than 50 microseconds, suggesting that rhodopsin and the P channel are closely coupled or form one ion channel complex. The Ca2+ dependence of the P current has been demonstrated with the established suction technique in a capacitive mode. The P current shows the maximum amplitude at only 300 nM Ca2+, and it gradually declines at higher Ca2+. In addition to Ca2+, the photoreceptor and the fast flagellar current can be carried by Sr2+ and Ba2+. Mg2+ is conducted less efficiently and at high concentrations blocks the photoreceptor channel. A motion analysis of the cells shows that only Ca2+ and Sr2+ can induce physiological stop responses, whereas the large Ba2+ currents cause abnormal long-lasting cell spiraling.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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