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      The initiation of excitation and light adaptation in Limulus ventral photoreceptors

      research-article
      The Journal of General Physiology
      The Rockefeller University Press

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          Abstract

          Two types of experiments indicate that light adaptation and excitation are initiated by the same, rather than different, populations of visual pigment. (a) The criterion action spectra of light adaptation and excitation are the same. (b) Increment-threshold curves were measured with a voltage-clamp technique under conditions of high and low concentration of plasma membrane rhodopsin (Rhpm). SD, the dark-adapted sensitivity, and 1/I2, the inverse of the background irradiance that desensitized by 0.3 log units, underwent the same fractional change when the rhodopsin concentration was changed. Both quantities appear to be linearly related to Rhpm. Reversible reductions in Rhpm were achieved by orange irradiation during a brief increase of extracellular pH from 7.8 to 10. This procedure would be unlikely to produce similar concentration changes in a hypothetical intracellular pigment because the concurrent change in intracellular pH, measured using the dye, phenol red, was only 0.45 pH units. It is thus unlikely that an intracellular pigment initiates light adaptation. On the assumption that light adaptation is mediated by a light-induced release of Ca++ from an intracellular store. the results reported here imply that an intracellular transmitter is needed to couple Rhpm to the intracellular store.

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          Author and article information

          Journal
          J Gen Physiol
          The Journal of General Physiology
          The Rockefeller University Press
          0022-1295
          1540-7748
          1 February 1979
          : 73
          : 2
          : 219-243
          Article
          79174593
          2215242
          438771
          c88231f1-f9a0-4e61-b7be-93f06171d5cb
          History
          Categories
          Articles

          Anatomy & Physiology
          Anatomy & Physiology

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