An Inwardly Rectifying Potassium Conductance Can Accelerate the
Hyperpolarizing Response in Retinal Horizontal Cells.
Dong, Cun-Jian and Frank S. Werblin.
Division of Neurobiology, Department of Molecular and Cell Biology, 145
LSA, University of California at Berkeley, Berkeley, CA 94720.
APStracts 2:0230N, 1995.
SUMMARY AND CONCLUSIONS
1). We studied the activation properties and assessed the functional role of
the inwardly rectifying potassium conductance (G K,IR ) in acutely isolated
retinal horizontal cells (HC s) using the whole-cell patch clamp technique.
2). The potassium current mediated by G K,IR was isolated using Cs - or Ba --
ions. This current was outward, although relatively small in amplitude, in the
voltage range between the potassium equilibrium potential (E K ) and 50- 60 mV
more positive. The current reversed its polarity at E K , and became inward at
potentials more negative than E K . When HC s were bathed in normal Ringer (E
K = -90 mV), G K,IR began to activate at about -30 mV, was 30 to 40% activated
at the resting potential (-70 to -80 mV) and about fully activated at -130 mV.
Thus, a significant portion of the activation range of G K,IR overlaps the HC
physiological response range (-20 to -80 mV). 3). G K,IR has a dramatic effect
on the kinetics of membrane polarization. Blocking G K,IR with Cs - or Ba --
significantly slowed the rate of membrane hyperpolarization in response to a
hyperpolarizing current ramp over the HC physiological response range.
Blocking G K,IR also dramatically slowed the onset rate of a simulated light
response generated by a brief break in a sustained glutamate puff. 4). These
results suggest that G K,IR can enhance the temporal resolution of the HC by
accelerating the onset rate of the hyperpolarizing light response.
Received 16 February 1995; accepted in final form 31 July 1995.
APS Manuscript Number J115-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.