Actions of Ca2+ on an Early Stage in Phototransduction Revealed by the
Dynamic Fall in Ca2+ Concentration during the Bright Flash Response
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Authors: | H.R. Matthews |
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Affiliation: | From the Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, United Kingdom |
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Abstract: | To study the actions of Ca2+ on “early” stages of the transduction cascade, changes in cytoplasmic calcium concentration (Ca2+i) were opposed by manipulating Ca2+ fluxes across the rod outer segment membraneimmediately following a bright flash. If the outer segment was exposed to 0 Ca2+/0 Na+ solution for a brief periodimmediately after the flash, then the period of response saturation was prolonged in comparison with that inRinger solution. But if the exposure to 0 Ca2+/0 Na+ solution instead came before or was delayed until 1 s afterthe flash then it had little effect. The degree of response prolongation increased with the duration of the exposure to 0 Ca2+/0 Na+ solution, revealing a time constant of 0.49 ± 0.03 s. By the time the response begins to recover from saturation, Ca2+i seems likely to have fallen to a similar level in each case. Therefore the prolongationof the response when Ca2+i was prevented from changing immediately after the flash seems likely to reflect the abolition of actions of the usual dynamic fall in Ca2+i on an early stage in the transduction cascade at a site which isavailable for only a brief period after the flash. One possibility is that the observed time constant corresponds tothe phosphorylation of photoisomerized rhodopsin. |
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Keywords: | photoreceptor retinal rod light adaptation calcium rhodopsin |
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