Role of Hyperpolarization-Activated Currents for the Intrinsic Dynamics of Isolated Retinal Neurons

• Published in: Biophysical journal Vol. 84; no. 4; pp. 2756 - 2767
• Main Authors: Mao, Bu-Qing, MacLeish, Peter R., Victor, Jonathan D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.04.2003; Biophysical Society; The Biophysical Society
• Subjects: Ambystoma tigrinum; Animals; Cells, Cultured; Computer Simulation; Electrophysiology; Interneurons - physiology; Membrane Potentials - physiology; Models, Neurological; Neurons; Potassium Channels - physiology; Potassium Channels, Inwardly Rectifying; Retina; Retina - physiology; Retinal Rod Photoreceptor Cells - physiology; Urodela
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(03)75080-2

The intrinsic dynamics of bipolar cells and rod photoreceptors isolated from tiger salamanders were studied by a patch-clamp technique combined with estimation of effective impulse responses across a range of mean membrane voltages. An increase in external K + reduces the gain and speeds the response in bipolar cells near and below resting potential. High external K + enhances the inward rectification of membrane potential, an effect mediated by a fast, hyperpolarization-activated, inwardly rectifying potassium current (K IR). External Cs + suppresses the inward-rectifying effect of external K +. The reversal potential of the current, estimated by a novel method from a family of impulse responses below resting potential, indicates a channel that is permeable predominantly to K +. Its permeability to Na +, estimated from Goldman-Hodgkin-Katz voltage equation, was negligible. Whereas the activation of the delayed-rectifier K + current causes bandpass behavior (i.e., undershoots in the impulse responses) in bipolar cells, activation of the K IR current does not. In contrast, a slow hyperpolarization-activated current (I h) in rod photoreceptors leads to pronounced, slow undershoots near resting potential. Differences in the kinetics and ion selectivity of hyperpolarization-activated currents in bipolar cells (K IR) and in rod photoreceptors (I h) confer different dynamical behavior onto the two types of neurons.