Role of hyperpolarization-activated currents for the intrinsic dynamics of isolated retinal neurons.
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.
Mao
Bu-Qing
BQ
Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York 10021, USA.
MacLeish
Peter R
PR
Victor
Jonathan D
JD
D000818:Animals; D002478:Cells, Cultured; D003198:Computer Simulation; D007395:Interneurons / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D008959:Models, Neurological; D015221:Potassium Channels / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D012160:Retina / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D014562:Caudata; D000098854:Kcnj10 Channel
D000098854:Kcnj10 Channel; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying