Modulation of transient outward potassium current by GTP, calcium, and glutamate in horizontal cells of the Xenopus retina

Modulation of transient outward potassium current by GTP, calcium, and glutamate in horizontal... Abstract 1. Membrane currents of luminosity horizontal cells (L-HCs) and chromatic horizontal cells (C-HCs) isolated from the Xenopus retina were characterized using the whole-cell patch-clamp technique. 2. The current-voltage curve for the L-HC had a characteristic negative slope conductance in the voltage range of -30 to -10 mV that was not evident in the C-HC. 3. A transient outward 4-aminopyridine-sensitive potassium current (A-current) was the most prominent current in C-HCs but was also present in L-HCs. A-current characteristics in the two horizontal cell (HC) classes were closely similar. Its threshold of activation was above -45 mV. The half-voltage of inactivation was close to -70 mV. The decay of the A-current was fit by a single exponential with time constants of 30 and 40 ms at depolarizing voltage steps to -10 and +30 mV, respectively. 4. The voltage for 50% A-current inactivation shifted toward negative potentials shortly after we established the whole-cell configuration. This shift was changed to more positive potentials by internal application of guanosine 5'-triphosphate, resulting in a significant overlap of A-current activation and inactivation functions near -40 mV, which is well within the normal operating range of the HC. 5. Internal application of the G-protein activator GTP gamma S shifted the voltage-dependent inactivation of the A-current toward positive potentials by +15 mV. In contrast, GDP beta S shifted the inactivation curve by about -10 mV, similar to what was observed in untreated cells. 6. GTP and GTP gamma S increased the rate of recovery from inactivation and slowed down the rate of inactivation of the A-current enabled by a depolarizing prepulse. 7. Glutamate superfused in the bath solution significantly accelerated the rate of inactivation of A-current induced by depolarizing prepulses. The rate of A-current recovery from inactivation, however, was not affected by glutamate. 8. Removal of calcium from the bath solution reversibly decreased the amplitude of the A-current without a significant shift in its threshold of activation. Copyright © 1994 the American Physiological Society http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Neurophysiology The American Physiological Society

Modulation of transient outward potassium current by GTP, calcium, and glutamate in horizontal cells of the Xenopus retina

Journal of Neurophysiology, Volume 71 (5): 1661 – May 1, 1994

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Publisher
The American Physiological Society
Copyright
Copyright © 1994 the American Physiological Society
ISSN
0022-3077
eISSN
1522-1598
Publisher site
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Abstract

Abstract 1. Membrane currents of luminosity horizontal cells (L-HCs) and chromatic horizontal cells (C-HCs) isolated from the Xenopus retina were characterized using the whole-cell patch-clamp technique. 2. The current-voltage curve for the L-HC had a characteristic negative slope conductance in the voltage range of -30 to -10 mV that was not evident in the C-HC. 3. A transient outward 4-aminopyridine-sensitive potassium current (A-current) was the most prominent current in C-HCs but was also present in L-HCs. A-current characteristics in the two horizontal cell (HC) classes were closely similar. Its threshold of activation was above -45 mV. The half-voltage of inactivation was close to -70 mV. The decay of the A-current was fit by a single exponential with time constants of 30 and 40 ms at depolarizing voltage steps to -10 and +30 mV, respectively. 4. The voltage for 50% A-current inactivation shifted toward negative potentials shortly after we established the whole-cell configuration. This shift was changed to more positive potentials by internal application of guanosine 5'-triphosphate, resulting in a significant overlap of A-current activation and inactivation functions near -40 mV, which is well within the normal operating range of the HC. 5. Internal application of the G-protein activator GTP gamma S shifted the voltage-dependent inactivation of the A-current toward positive potentials by +15 mV. In contrast, GDP beta S shifted the inactivation curve by about -10 mV, similar to what was observed in untreated cells. 6. GTP and GTP gamma S increased the rate of recovery from inactivation and slowed down the rate of inactivation of the A-current enabled by a depolarizing prepulse. 7. Glutamate superfused in the bath solution significantly accelerated the rate of inactivation of A-current induced by depolarizing prepulses. The rate of A-current recovery from inactivation, however, was not affected by glutamate. 8. Removal of calcium from the bath solution reversibly decreased the amplitude of the A-current without a significant shift in its threshold of activation. Copyright © 1994 the American Physiological Society

Journal

Journal of NeurophysiologyThe American Physiological Society

Published: May 1, 1994

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