Journal of Neurophysiology, Vol 64, Issue 6 1758-1766, Copyright © 1990 by APS
Sustained and transient potassium currents of cultured horizontal cells isolated from white bass retina
J. M. Sullivan and E. M. Lasater
University of Utah School of Medicine, Department of Physiology, Salt Lake City 84108.
1. Horizontal cells (HCs) are second-order neurons in the retina that
receive direct photoreceptor input. They rest at around -20 mV in the dark,
because of the continuous release of neurotransmitter from photoreceptors.
HCs respond to light with graded hyperpolarizations, which can reach -70 to
-80 mV in the presence of very bright stimuli. 2. HCs from the retinas of
white bass were isolated and maintained in culture. Potassium currents in
three morphological types of HCs--H1, H2, and H4--were studied in culture
with whole-cell, patch-clamp techniques, when sodium and calcium currents
were blocked. 3. A transient outward potassium current (IA), with many
characteristics of the A-current, was found in all H2s and H4s but only
occasionally in H1s. The threshold for activation of this current was
around -40 mV, a value more depolarized than usual for the A-current. The
peak IA was typically smaller than 300 pA when the membrane was stepped
from a holding potential of -70 mV to a command potential of -10 mV, the
upper limit of the in vivo range of HC membrane potentials. Steady-state
inactivation is expected to reduce the magnitude of IA in vivo. 4. A
sustained outward potassium current (IK) was found in all types of HCs.
This sustained potassium current did not activate until the membrane was
stepped to potentials above -10 mV, a value much more depolarized than
those reported for the delayed rectifier current in other neurons. As a
result, IK is absent over the in vivo operating range of these cells. 5. No
calcium-dependent potassium current was found in any cells.(ABSTRACT
TRUNCATED AT 250 WORDS)
