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The Journal of Neuroscience, October 15, 2000, 20(20):7564-7570
C-Terminal Alternative Splicing Changes the Gating Properties of
a Human Spinal Cord Calcium Channel 1A Subunit
Howard S.
Krovetz,
Thomas D.
Helton,
Anne L.
Crews, and
William A.
Horne
Department of Anatomy, Physiological Sciences, and Radiology, North
Carolina State University College of Veterinary Medicine, Raleigh,
North Carolina 27606
The calcium channel 1A subunit gene codes for
proteins with diverse structure and function. This diversity may be
important for fine tuning neurotransmitter release at central and
peripheral synapses. The 1A C terminus, which serves a
critical role in processing information from intracellular signaling
molecules, is capable of undergoing extensive alternative splicing. The
purpose of this study was to determine the extent to which C-terminal alternative splicing affects some of the fundamental biophysical properties of 1A subunits. Specifically, the biophysical
properties of two alternatively spliced 1A subunits were
compared. One variant was identical to an isoform identified previously
in human brain, and the other was a novel isoform isolated from human
spinal cord. The variants differed by two amino acids (NP) in the
extracellular linker between transmembrane segments IVS3 and IVS4 and
in two C-terminal regions encoded by exons 37 and 44. Expression in
Xenopus oocytes demonstrated that the two variants were
similar with respect to current-voltage relationships and the voltage
dependence of steady-state activation and inactivation. However, the
rates of activation, inactivation, deactivation, and recovery from
inactivation were all significantly slower for the spinal cord variant.
A chimeric strategy demonstrated that the inclusion of the sequence
encoded by exon 44 specifically affects the rate of inactivation. These findings demonstrate that C-terminal structural changes alone can
influence the way in which 1A subunits respond to a
depolarizing stimulus and add to the developing picture of the C
terminus as a critical domain in the regulation of
Ca2+ channel function.
Key words:
spinal cord; cerebellum; calcium channel; 1A subunit; voltage clamp; alternative splicing; C terminus
Copyright © 2000 Society for Neuroscience 0270-6474/00/20207564-07$05.00/0
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