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Rectification of cGMP‐activated channels induced by phosphorylation in dogfish retinal ‘on’ bipolar cells
Author(s) -
Shiells R. A.,
Falk G.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.00697.x
Subject(s) - biophysics , chemistry , phosphorylation , gating , membrane potential , hyperpolarization (physics) , inhibitory postsynaptic potential , reversal potential , patch clamp , microbiology and biotechnology , neuroscience , biology , biochemistry , receptor , stereochemistry , nuclear magnetic resonance spectroscopy
1 Whole‐cell current responses to brief flashes were obtained from voltage‐clamped ‘on’ bipolar cells in dark‐adapted dogfish retinal slices. When internal Ca 2+ was buffered to low levels, the current‐voltage ( I‐V) relation of their flash responses was linear, with a reversal potential near 0 mV. 2 On elevating internal Ca 2+ the light‐dependent I‐V relation showed outward rectification, such that the current response to a flash decreased e‐fold for a hyperpolarization of 22 mV. 3 Inclusion of a CaMKII inhibitory peptide in the patch‐pipette solution removed the rectification even in the presence of 50 μ m Ca 2+ . 4 These results are consistent with CaMKII phosphorylation of cGMP‐activated channels leading to a voltage‐dependent reduction in conductance (outward rectification) and a reduced light response. The voltage‐dependent property suggests that phosphorylation creates an energy barrier near the outer part of the channel, reducing the flow principally of monovalent cations. 5 This is the first reported instance of CaMKII phosphorylation acting to change the electrical characteristics of a membrane channel from linear to rectifying. 6 Ca 2+ ‐dependent desensitization by background light and channel rectification may underlie the change in centre‐surround organization of the visual system with light adaptation.