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Photopotential and light-induced protonation changes in ROD outer segment membranes
710
Abstracts
PHOTOPOTENTIAL A N D LIGHT-INDUCED PROTONATION CHANGES IN ROD OUTER SEGMENT MEMBRANES M. A. OSTROVKSY, G. R. KALAMKAROV a n d T. F. SHEVCHENKO Institute of Chemical Physics, U.S.S.R. Academy of Sciences, U.S.S.R. It has been previously found using penetrating ions [1] and direct electrometric measurements [2, 3] that a photopotential appears on the photoreceptor membrane (plus sign on the inside disc surface). From the comparison of this potential and the well-known early receptor potential it is possible to conclude that the disc membrane electrical resistance is significantly higher than the ,,plasma membrane one [4]. The kinetics of the photoinduced protonation changes of the rhodopsin in the membrane was studied. It has been observed that the rhodopsin to metarhodopsin II transition is followed by proton uptake, but the illumination of the metarhodopsin II intermediate results in the proton release. Photopotentials of both polarities were similarly registered on the disc with light absorption by rhodopsin and metarhodopsin II. It can be suggested that the nature of the photopotential is similar to the protonation changes from the comparison of their kinetics. We have obtained a fraction of inverted photoreceptor discs using rapid freezing followed by separation on a concanavolin-A-sepharose column. The illumination of such a fraction results in proton release, opposite to the normal oriented disc fraction. One could propose that protons transfer across the disc membrane in/during rhodopsin photolysis. 1. 2. 3. 4.
Bolshakov V. I., Kalamkarov G. R. and Ostrovsky M. A. Dokl. Acad. Nauk. S S S R 240, 1241 (1978). Bolshakov V. I., Kalamkarov G. R. and Ostrovsky M. A. Dokl. Akad. Nauk. S S S R 249, 1485 (1979). Drachev L. A. et al. Eur. J. Biochem. 117, 471 (1981). Rebrik T. I., Kalamkarov G. R. and Ostrovsky M. A. Dokl. Akad. Nauk. S S S R 258, 229 (1981).
PHOTOELECTRIC SIGNALS RECORDED FROM A LIPID BILAYER M E M B R A N E TO WHICH BOVINE DISK MEMBRANES ARE ATTACHED P. J. BAUER1, A. FAHR 2 a n d E. BAMBERG3 qnstitut fiir Neurobiologie, KFA D-5170 Jfilich, 2Department of Physics, FU-Berlin, D-1000 Berlin and 3MPI of Biophysics, D-6000 Frankfurt, F.R.G. Whole disk membranes and disk vesicles prepared by sonication were added to one side of a black lipid bilayer membrane. A dye laser flash (500 nm, 10 nsec) delivered 10-20 min after addition of the disks elicited a photovoltage across the bilayer membrane which decreased for successive laser flashes indicating that the photoresponse is due to bleaching of rhodopsin. At normal ionic strength (100 mM KCI) the photovoltage was negative on the rhodopsin containing side of the bilayer membrane measured against the rhodopsin-free side, however at low ionic strength (10 mM KCI) the polarity of the photovoltage was positive for osmotically intact disks. The experiments indicate a transient light-induced permeability change of disk membranes occurring in the millisecond time range.
C A D M I U M EXERTS BOTH A N EXCITATORY A N D A N INHIBITORY EFFECT ON BULLFROG CONES D. A. BOLNICK, J. B. BOSETTI, L. W. HAYNES, A. E. WALTER a n d A. J. SILLMAN Department of Animal Physiology, University of California, Davis, CA 95616, U.S.A. The mass receptor potential of the excised, superfused bullfrog retina was isolated by treatment with Na-aspartate. Cone responses were monitored without interference from rods using a two flash technique previously described [1]. The effect of cadmium (1.0 to 400.0 # M CdC12) was complex, characterized by a purely excitatory component at the lower levels and an inhibitory component that became evident at 75.0 # M. The maximum increase in cone response amplitude due to the excitatory component was about 60~o at 100.0 #M. At 400.0#M, the highest concentration examined in this study, the cone response
Abstracts
PHOTOPOTENTIAL A N D LIGHT-INDUCED PROTONATION CHANGES IN ROD OUTER SEGMENT MEMBRANES M. A. OSTROVKSY, G. R. KALAMKAROV a n d T. F. SHEVCHENKO Institute of Chemical Physics, U.S.S.R. Academy of Sciences, U.S.S.R. It has been previously found using penetrating ions [1] and direct electrometric measurements [2, 3] that a photopotential appears on the photoreceptor membrane (plus sign on the inside disc surface). From the comparison of this potential and the well-known early receptor potential it is possible to conclude that the disc membrane electrical resistance is significantly higher than the ,,plasma membrane one [4]. The kinetics of the photoinduced protonation changes of the rhodopsin in the membrane was studied. It has been observed that the rhodopsin to metarhodopsin II transition is followed by proton uptake, but the illumination of the metarhodopsin II intermediate results in the proton release. Photopotentials of both polarities were similarly registered on the disc with light absorption by rhodopsin and metarhodopsin II. It can be suggested that the nature of the photopotential is similar to the protonation changes from the comparison of their kinetics. We have obtained a fraction of inverted photoreceptor discs using rapid freezing followed by separation on a concanavolin-A-sepharose column. The illumination of such a fraction results in proton release, opposite to the normal oriented disc fraction. One could propose that protons transfer across the disc membrane in/during rhodopsin photolysis. 1. 2. 3. 4.
Bolshakov V. I., Kalamkarov G. R. and Ostrovsky M. A. Dokl. Acad. Nauk. S S S R 240, 1241 (1978). Bolshakov V. I., Kalamkarov G. R. and Ostrovsky M. A. Dokl. Akad. Nauk. S S S R 249, 1485 (1979). Drachev L. A. et al. Eur. J. Biochem. 117, 471 (1981). Rebrik T. I., Kalamkarov G. R. and Ostrovsky M. A. Dokl. Akad. Nauk. S S S R 258, 229 (1981).
PHOTOELECTRIC SIGNALS RECORDED FROM A LIPID BILAYER M E M B R A N E TO WHICH BOVINE DISK MEMBRANES ARE ATTACHED P. J. BAUER1, A. FAHR 2 a n d E. BAMBERG3 qnstitut fiir Neurobiologie, KFA D-5170 Jfilich, 2Department of Physics, FU-Berlin, D-1000 Berlin and 3MPI of Biophysics, D-6000 Frankfurt, F.R.G. Whole disk membranes and disk vesicles prepared by sonication were added to one side of a black lipid bilayer membrane. A dye laser flash (500 nm, 10 nsec) delivered 10-20 min after addition of the disks elicited a photovoltage across the bilayer membrane which decreased for successive laser flashes indicating that the photoresponse is due to bleaching of rhodopsin. At normal ionic strength (100 mM KCI) the photovoltage was negative on the rhodopsin containing side of the bilayer membrane measured against the rhodopsin-free side, however at low ionic strength (10 mM KCI) the polarity of the photovoltage was positive for osmotically intact disks. The experiments indicate a transient light-induced permeability change of disk membranes occurring in the millisecond time range.
C A D M I U M EXERTS BOTH A N EXCITATORY A N D A N INHIBITORY EFFECT ON BULLFROG CONES D. A. BOLNICK, J. B. BOSETTI, L. W. HAYNES, A. E. WALTER a n d A. J. SILLMAN Department of Animal Physiology, University of California, Davis, CA 95616, U.S.A. The mass receptor potential of the excised, superfused bullfrog retina was isolated by treatment with Na-aspartate. Cone responses were monitored without interference from rods using a two flash technique previously described [1]. The effect of cadmium (1.0 to 400.0 # M CdC12) was complex, characterized by a purely excitatory component at the lower levels and an inhibitory component that became evident at 75.0 # M. The maximum increase in cone response amplitude due to the excitatory component was about 60~o at 100.0 #M. At 400.0#M, the highest concentration examined in this study, the cone response