Sustained and transient potassium currents of cultured horizontal cells isolated from white bass retina.
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)
Sullivan
J M
JM
University of Utah School of Medicine, Department of Physiology, Salt Lake City 84108.
Lasater
E M
EM
D000632:Aminopyrine / Q000494:pharmacology; D000818:Animals; D001492:Bass / Q000502:physiology*; D002478:Cells, Cultured; D004566:Electrodes; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D012160:Retina / Q000166:cytology / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D000632:Aminopyrine; D019789:Tetraethylammonium; D011188:Potassium