Journal of Neurophysiology, Vol 64, Issue 6 1917-1928, Copyright © 1990 by APS

ARTICLES

Inward rectification in the inner segment of single retinal cone photoreceptors

A. V. Maricq and J. I. Korenbrot
Department of Physiology, School of Medicine, University of California, San Francisco 94143.

1. Single cone photoreceptors were dissociated from the retina of a lizard with the aid of papain. The majority of the cells lost their outer segments but had well-preserved, large synaptic pedicles. Electrical properties of the cells were studied with tight-seal electrodes in the whole cell configuration. On the average, cone inner segments had a resting potential of -55 mV, and at this potential their input resistance was 2.6 G omega and their capacitance was 8 pF. 2. Under current clamp the cones exhibited a pronounced anomalous voltage rectification in response to hyperpolarizing currents. The voltage rectification was eliminated by external Cs+. 3. The Cs(+)-sensitive current underlying voltage rectification was isolated by blocking other currents present in the cone. Co2+ blocked a voltage-dependent Ca2+ current and a Ca2(+)-dependent Cl- current, and tetraethylammonium (TEA)+ blocked a delayed-rectifier K+ current. 4. The Cs(+)-sensitive current was activated by hyperpolarization to potentials more negative than -50 mV, and its current-voltage (I-V) relationship exhibited inward rectification. 5. The inward-rectifying current was selective for K+, but not exclusively. Increasing external K+ concentration 10-fold shifted the reversal potential by 13 mV. If Na ions also permeate through the inward-rectifying channels, the ratio of permeabilities (PK+/PNa+) in normal solution is approximately 3.9. 6. The kinetics of the inward-rectifying current were described by the sum of two exponentials, the amplitudes and time constants of which were voltage dependent. 7. The voltage dependence of the inward-rectifying current was described by Boltzmann's function, with half-maximum activation at -79 mV and a steepness parameter of 7.5 mV. 8. The voltage dependence and kinetics of the inward-rectifying current suggest that it is inactive in a cone photoreceptor in the dark. However, it becomes activated in the course of large hyperpolarizations generated by bright-light illumination. This activity will modify the waveform of the photovoltage--the current will generate a depolarizing component that opposes the light-generated hyperpolarization.

This article has been cited by other articles:

				S. C. Lee and A. T. Ishida Ih Without Kir in Adult Rat Retinal Ganglion Cells J Neurophysiol, May 1, 2007; 97(5): 3790 - 3799. [Abstract] [Full Text] [PDF]

				D. Holcman and J. I. Korenbrot The Limit of Photoreceptor Sensitivity: Molecular Mechanisms of Dark Noise in Retinal Cones J. Gen. Physiol., May 31, 2005; 125(6): 641 - 660. [Abstract] [Full Text] [PDF]

				F. Kawai, M. Horiguchi, H. Ichinose, M. Ohkuma, R. Isobe, and E.-i. Miyachi Suppression by an h Current of Spontaneous Na+ Action Potentials in Human Cone and Rod Photoreceptors Invest. Ophthalmol. Vis. Sci., January 1, 2005; 46(1): 390 - 397. [Abstract] [Full Text] [PDF]

				T. I. Rebrik and J. I. Korenbrot In Intact Mammalian Photoreceptors, Ca2+-dependent Modulation of cGMP-gated Ion Channels Is Detectable in Cones but Not in Rods J. Gen. Physiol., December 29, 2003; 123(1): 63 - 76. [Abstract] [Full Text] [PDF]

				B.-Q. Mao, P. R. MacLeish, and J. D. Victor Role of Hyperpolarization-Activated Currents for the Intrinsic Dynamics of Isolated Retinal Neurons Biophys. J., April 1, 2003; 84(4): 2756 - 2767. [Abstract] [Full Text] [PDF]

				B. A. Hughes, G. Kumar, Y. Yuan, A. Swaminathan, D. Yan, A. Sharma, L. Plumley, T. L. Yang-Feng, and A. Swaroop Cloning and functional expression of human retinal Kir2.4, a pH-sensitive inwardly rectifying K+ channel Am J Physiol Cell Physiol, September 1, 2000; 279(3): C771 - C784. [Abstract] [Full Text] [PDF]

				R. Bal and D. Oertel Hyperpolarization-Activated, Mixed-Cation Current (Ih) in Octopus Cells of the Mammalian Cochlear Nucleus J Neurophysiol, August 1, 2000; 84(2): 806 - 817. [Abstract] [Full Text] [PDF]

				D. M. Schneeweis and J. L. Schnapf The Photovoltage of Macaque Cone Photoreceptors: Adaptation, Noise, and Kinetics J. Neurosci., February 15, 1999; 19(4): 1203 - 1216. [Abstract] [Full Text] [PDF]

				E. N. Yamoah, L. Matzel, and T. Crow Expression of Different Types of Inward Rectifier Currents Confers Specificity of Light and Dark Responses in Type A and B Photoreceptors of Hermissenda J. Neurosci., August 15, 1998; 18(16): 6501 - 6511. [Abstract] [Full Text] [PDF]

				D. W. Crevier and M. Meister Synchronous Period-Doubling in Flicker Vision of Salamander and Man J Neurophysiol, April 1, 1998; 79(4): 1869 - 1878. [Abstract] [Full Text] [PDF]

				L. Gaal, B. Roska, S. A. Picaud, S. M. Wu, R. Marc, and F. S. Werblin Postsynaptic Response Kinetics Are Controlled by a Glutamate Transporter at Cone Photoreceptors J Neurophysiol, January 1, 1998; 79(1): 190 - 196. [Abstract] [Full Text] [PDF]

				S.-F. Fan and S. Yazulla Electrogenic Hyperpolarization-Elicited Chloride Transporter Current in Blue Cones of Zebrafish Retinal Slices J Neurophysiol, March 1, 1997; 77(3): 1447 - 1459. [Abstract] [Full Text] [PDF]