Journal of Neuroscience, Vol 6, 2521-2526, Copyright © 1986 by Society for Neuroscience
Comparison of the light-sensitive and cyclic GMP-sensitive conductances of the rod photoreceptor: noise characteristics
G Matthews
Patch-clamp recordings were made from outer segments of single rod
photoreceptors isolated from toad retina. Cyclic GMP (cGMP) and its
hydrolysis-resistant analog, 8-bromo-cGMP, increased the conductance of
excised membrane patches when applied to the intracellular face of the
membrane but not when applied to the extracellular face. The rectification
properties of the cGMP-dependent conductance depended on the concentration
of divalent cations bathing the intra- and extracellular membrane faces.
Current flow was favored from the side of the membrane, either internal or
external, that was exposed to bathing fluid free of divalent cations. The
power spectral density of cGMP- induced noise was fitted by a sum of 2
Lorentzian components, with corner frequencies differing approximately
15-fold on average. This suggests that channel gating is controlled by 2
kinetic components. To compare the cGMP-sensitive conductance with the
light-sensitive conductance of the rod, cell-attached patch-clamp
recordings were made from intact, dark-adapted rods, and noise arising from
the light- sensitive conductance was analyzed. The power spectrum of the
light- sensitive noise also exhibited 2 Lorentzian components similar to
those of the cGMP-sensitive conductance in excised patches. These results
are consistent with the idea that cGMP opens the light-sensitive channel of
the rod outer segment.
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