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The Journal of Neuroscience, March 1, 2000, 20(5):1685-1693
Coexpression of Cloned  1B,  2a, and
2/ Subunits Produces
Non-Inactivating Calcium Currents Similar to Those
Found in Bovine Chromaffin Cells
Anne L.
Cahill,
Joyce H.
Hurley, and
Aaron P.
Fox
The Department of Neurobiology, Pharmacology, and Physiology, The
University of Chicago, Chicago, Illinois 60637
Chromaffin cells express N-type calcium channels identified
on the basis of their high sensitivity to block by  -conotoxin GVIA (-CgTx GVIA). In contrast to neuronal N-type calcium
currents that inactivate during long depolarizations and that require
negative holding potentials to remove inactivation, many chromaffin
cells exhibit N-type calcium channel currents that show little
inactivation during maintained depolarizations and that exhibit no
decrease in channel availability at depolarized holding potentials.
N-type calcium channels are thought to be produced by combination of the pore-forming  1B subunit and accessory  and
2/ subunits. To examine the molecular
composition of the non-inactivating N-type calcium channel, we cloned
the 1B and accessory (1b,
1c, 2a, 2b,
and 3a) subunits found in bovine chromaffin
cells. Expression of the subunits in either Xenopus
oocytes or human embryonic kidney 293 cells produced
high-threshold calcium currents that were blocked by -CgTx GVIA.
Coexpression of bovine 1B with 1b,
1c, 2b, or 3a
produced currents that were holding potential dependent. In contrast,
coexpression of bovine 1B with 2a
produced holding potential-independent calcium currents that closely
mimicked native non-inactivating currents, suggesting that
non-inactivating N-type channels consist of bovine
1B, 2/, and
2a.
Key words:
N-type calcium channel; 1B subunit;
subunits; non-inactivating calcium current; chromaffin cells; voltage-dependent calcium channel
Copyright © 2000 Society for Neuroscience 0270-6474/00/2051685-09$05.00/0
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