Abstract
Vertebrate photoreceptors respond to light by a membrane hyperpolarization which is thought to result from the decrease of a Na-selective conductance in the outer segment1–6. One hypothesis is that light increases intracellular free Ca which reversibly blocks the Na conductance7,8; at least part of this Ca is then extruded to the cell exterior by a Na–Ca exchanger at the plasma membrane9–14. We describe experiments here which show that the light-sensitive conductance in rods is also highly permeable to K. While external Na acts to keep the conductance open, external K tends to keep it closed, both actions probably involving the Na–Ca exchanger. The conductance is also permeable to the monovalent cations Li, Rb and Cs and the divalent cations Ca, Sr and Ba. The ability of both Na and K to go through the light-sensitive conductance explains the long-standing puzzle as to why the reversal potential for the light response is at 0 to +10 mV15–17.
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Yau, KW., Nakatani, K. Cation selectivity of light-sensitive conductance in retinal rods. Nature 309, 352–354 (1984). https://doi.org/10.1038/309352a0
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DOI: https://doi.org/10.1038/309352a0
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