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Journal of Neuroscience, Vol 16, 2430-2443, Copyright © 1996 by Society for Neuroscience
Beta subunit coexpression and the alpha1 subunit domain I-II linker affect piperidine block of neuronal calcium channels
GW Zamponi, TW Soong, E Bourinet and TP Snutch
Biotechnology Laboratory, University of British Columbia, Vancouver, Canada.
The effects of local anesthetics were examined on a family of transiently
expressed neuronal calcium channels. Fomocaine, a local anesthetic
containing a morpholine ring, preferentially blocked alpha1E channels (Ki =
100 microM), and had a lower affinity (3- to 15-fold) for alpha1A, alpha1B,
and alpha1C channels. Block was incompletely reversible, followed 1:1
kinetics, and did not affect steady-state inactivation properties.
Fomocaine block was sensitive to the concentration of permeant ion and
enhanced in the presence of external pore blockers, suggesting a site of
action in the conducting pathway. Flecainide, which carries a piperidine
ring, and the diphenylbutylpiperidine antipsychotic, penfluridol, caused
qualitatively similar block, suggesting that morpholine rings are
compatible with the piperidine receptor site. In contrast, procaine, which
contains an alkyl chain, caused reversible low affinity block of the
different calcium channels (Kd values between 2 and 5 mM) and was least
effective on alpha1E and did not compete with fomocaine, suggesting that
local anesthetics interact with at least two distinct receptor sites.
Compared to coexpression with the Ca channel beta1b subunit, block at the
piperidine receptor site was significantly weakened with the beta2a subunit
suggesting that the nature of the beta subunit contributes to drug binding.
Amino acid changes in the cytoplasmic linker between domains I and II
resulted in decreased fomocaine and penfluridol blocking affinity.
Furthermore, the blocking affinity observed with alpha1B, was conferred on
alpha1A by substitution of the domain I-II linker of alpha1B into alpha1A.
Taken together, the data suggest that beta subunit binding and the domain
I- II linker contribute to the piperidine receptor site on neuronal calcium
channels.
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