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The Journal of Neurophysiology Vol. 86 No. 1 July 2001, pp. 130-142
Copyright ©2001 by the American Physiological Society
1Department of Physiology and Neuroscience, 2Department of Pediatric Cardiology, and 3Department of Biochemistry, New York University School of Medicine, New York, New York 10016
Vega-Saenz de Miera, Eleazar,
David H. P. Lau,
Maria Zhadina,
David Pountney,
William A. Coetzee, and
Bernardo Rudy.
KT3.2 and KT3.3, Two Novel Human Two-Pore K+ Channels
Closely Related to TASK-1. J. Neurophysiol. 86: 130-142, 2001. We report the cloning of
human KT3.2 and KT3.3 new members of the two-pore
K+ channel (KT) family. Based on amino acid
sequence and phylogenetic analysis, KT3.2, KT3.3, and TASK-1 constitute
a subfamily within the KT channel mammalian family. When
Xenopus oocytes were injected with KT3.2 cRNA, the resting
membrane potential was brought close to the potassium equilibrium
potential. At low extracellular K+
concentrations, two-electrode voltage-clamp recordings revealed the
expression of predominantly outward currents. With high extracellular K+ (98 mM), the current-voltage relationship
exhibited weak outward rectification. Measurement of reversal
potentials at different [K+]o revealed a slope of
48 mV per 10-fold change in K+ concentration as
expected for a K+-selective channel. Unlike
TASK-1, which is highly sensitive to changes of pH in the physiological
range, KT3.2 currents were relatively insensitive to changes in
intracellular or extracellular pH within this range due to a shift in
the pH dependency of KT3.2 of 1 pH unit in the acidic direction. On the
other hand, the phorbol ester phorbol 12-myristate 13-acetate
(PMA), which does not affect TASK-1, produces strong inhibition
of KT3.2 currents. Human KT3.2 mRNA expression was most prevalent in
the cerebellum. In rat, KT3.2 is exclusively expressed in the brain,
but it has a wide distribution within this organ. High levels of
expression were found in the cerebellum, medulla, and thalamic nuclei.
The hippocampus has a nonhomogeneous distribution, expressing at
highest levels in the lateral posterior and inferior portions. Medium
expression levels were found in neocortex. The KT3.2 gene is located at
chromosome 8q24 1-3, and the KT3.3 gene maps to chromosome
20q13.1.
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