Abstract
Rhodopsin-mediated photoreceptor currents, I(P), of the unicellular alga Chlamydomonas reinhardtii were studied under neutral and acidic conditions. We characterized the kinetically overlapping components of the first, flash-induced inward current recorded from the eye, I(P1), as a low- and high-intensity component, I(P1a) and I(P1b), respectively. They peak between 1 and 10 ms after the light-flash and are both likely to be carried by Ca(2+). I(P1a) and I(P1b) exhibit half-maximal photon flux densities, Q(1/2), of approximately 0.14 and 58 microE m(-2), and maximal amplitudes of approximately 4.9 and 38 pA, respectively. At acidic extracellular pH values (pH 3-5), both I(P1) currents are followed by distinct H(+) currents, I(P2a) and I(P2b), with maxima after approximately 5 and 100 ms, respectively. Because the Q(1/2) values of I(P1b) and I(P2b) virtually coincide with Q(1/2) of rhodopsin bleaching, we suggest that the respective conductances G(1b) and G(2b) are closely coupled to the rhodopsin, whereas the low light-saturating conductances G(1a) and G(2a) reflect transducer-activated states of a second rhodopsin photoreceptor system.
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- Beck C., Uhl R. On the localization of voltage-sensitive calcium channels in the flagella of Chlamydomonas reinhardtii. J Cell Biol. 1994 Jun;125(5):1119–1125. doi: 10.1083/jcb.125.5.1119. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Beckmann M., Hegemann P. In vitro identification of rhodopsin in the green alga Chlamydomonas. Biochemistry. 1991 Apr 16;30(15):3692–3697. doi: 10.1021/bi00229a014. [DOI] [PubMed] [Google Scholar]
- Blatt M. R., Gradmann D. K(+)-sensitive gating of the K+ outward rectifier in Vicia guard cells. J Membr Biol. 1997 Aug 1;158(3):241–256. doi: 10.1007/s002329900261. [DOI] [PubMed] [Google Scholar]
- Braun F. J., Hegemann P. Direct measurement of cytosolic calcium and pH in living Chlamydomonas reinhardtii cells. Eur J Cell Biol. 1999 Mar;78(3):199–208. doi: 10.1016/S0171-9335(99)80099-5. [DOI] [PubMed] [Google Scholar]
- Braun F. J., Hegemann P. Two light-activated conductances in the eye of the green alga Volvox carteri. Biophys J. 1999 Mar;76(3):1668–1678. doi: 10.1016/S0006-3495(99)77326-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Foster K. W., Smyth R. D. Light Antennas in phototactic algae. Microbiol Rev. 1980 Dec;44(4):572–630. doi: 10.1128/mr.44.4.572-630.1980. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Govorunova E. G., Sineshchekov O. A., Gärtner W., Chunaev A. S., Hegemann P. Photoreceptor current and photoorientation in chlamydomonas mediated by 9-demethylchlamyrhodopsin. Biophys J. 2001 Nov;81(5):2897–2907. doi: 10.1016/S0006-3495(01)75930-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Govorunova E. G., Sineshchekov O. A., Hegemann P. Desensitization and Dark Recovery of the Photoreceptor Current in Chlamydomonas reinhardtii. Plant Physiol. 1997 Oct;115(2):633–642. doi: 10.1104/pp.115.2.633. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hegemann P., Gärtner W., Uhl R. All-trans retinal constitutes the functional chromophore in Chlamydomonas rhodopsin. Biophys J. 1991 Dec;60(6):1477–1489. doi: 10.1016/S0006-3495(91)82183-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Holland E. M., Braun F. J., Nonnengässer C., Harz H., Hegemann P. The nature of rhodopsin-triggered photocurrents in Chlamydomonas. I. Kinetics and influence of divalent ions. Biophys J. 1996 Feb;70(2):924–931. doi: 10.1016/S0006-3495(96)79635-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Holland E. M., Harz H., Uhl R., Hegemann P. Control of phobic behavioral responses by rhodopsin-induced photocurrents in Chlamydomonas. Biophys J. 1997 Sep;73(3):1395–1401. doi: 10.1016/S0006-3495(97)78171-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lawson M. A., Zacks D. N., Derguini F., Nakanishi K., Spudich J. L. Retinal analog restoration of photophobic responses in a blind Chlamydomonas reinhardtii mutant. Evidence for an archaebacterial like chromophore in a eukaryotic rhodopsin. Biophys J. 1991 Dec;60(6):1490–1498. doi: 10.1016/S0006-3495(91)82184-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Litvin F. F., Sineshchekov O. A., Sineshchekov V. A. Photoreceptor electric potential in the phototaxis of the alga Haematococcus pluvialis. Nature. 1978 Feb 2;271(5644):476–478. doi: 10.1038/271476a0. [DOI] [PubMed] [Google Scholar]
- Malhotra B., Glass ADM. Potassium Fluxes in Chlamydomonas reinhardtii (I.Kinetics and Electrical Potentials). Plant Physiol. 1995 Aug;108(4):1527–1536. doi: 10.1104/pp.108.4.1527. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Nonnengässer C., Holland E. M., Harz H., Hegemann P. The nature of rhodopsin-triggered photocurrents in Chlamydomonas. II. Influence of monovalent ions. Biophys J. 1996 Feb;70(2):932–938. doi: 10.1016/S0006-3495(96)79636-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sineshchekov O. A., Govorunova E. G., Dér A., Keszthelyi L., Nultsch W. Photoinduced electric currents in carotenoid-deficient Chlamydomonas mutants reconstituted with retinal and its analogs. Biophys J. 1994 Jun;66(6):2073–2084. doi: 10.1016/S0006-3495(94)81002-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sineshchekov O. A., Litvin F. F., Keszthelyi L. Two components of photoreceptor potential in phototaxis of the flagellated green alga Haematococcus pluvialis. Biophys J. 1990 Jan;57(1):33–39. doi: 10.1016/S0006-3495(90)82504-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sineshchekov OA, Govorunova EG. Rhodopsin-mediated photosensing in green flagellated algae. Trends Plant Sci. 1999 Feb;4(2):58–63. doi: 10.1016/s1360-1385(98)01370-3. [DOI] [PubMed] [Google Scholar]
- Stavis R. L., Hirschberg R. Phototaxis in Chlamydomonas reinhardtii. J Cell Biol. 1973 Nov;59(2 Pt 1):367–377. doi: 10.1083/jcb.59.2.367. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Takahashi T., Yoshihara K., Watanabe M., Kubota M., Johnson R., Derguini F., Nakanishi K. Photoisomerization of retinal at 13-ene is important for phototaxis of Chlamydomonas reinhardtii: simultaneous measurements of phototactic and photophobic responses. Biochem Biophys Res Commun. 1991 Aug 15;178(3):1273–1279. doi: 10.1016/0006-291x(91)91031-7. [DOI] [PubMed] [Google Scholar]
- Uhl R., Hegemann P. Probing visual transduction in a plant cell: Optical recording of rhodopsin-induced structural changes from Chlamydomonas reinhardtii. Biophys J. 1990 Nov;58(5):1295–1302. doi: 10.1016/S0006-3495(90)82469-3. [DOI] [PMC free article] [PubMed] [Google Scholar]