Biophysical Journal 66: 360-365 (1994)
© 1994 the Biophysical Society

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Analysis of fluctuations in the cGMP-dependent currents of cone photoreceptor outer segments.

Department of Physiology, University of California Medical School, San Francisco 94143.

ABSTRACT

We measured cGMP-dependent currents, under voltage clamp, in membrane patches detached from the outer segment of single-cone photoreceptors isolated from the retina of striped bass. We analyzed the variance of the current about its mean and the spectral density distribution of the current fluctuations. From the analysis of variance, we determined that the cGMP-gated channels increase their probability of opening with increasing cGMP up to a maximum value of 0.87 +/- 0.03. The dependence on cGMP of the probability of opening is well described by a Hill equation with Km = 60.2 +/- 3.7 microM and n = 2.33 +/- 0.32 at -50 mV. At the same voltage, the spectral density distribution is well fit by the sum of two Lorentzians with corner frequencies at 26 +/- 18 and 318 +/- 58 Hz. The single-channel conductance calculated from the current noise by two different methods suggests that the most frequently occupied conductance state has an amplitude of about 18 pS.