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The Journal of Neuroscience, July 15, 1998, 18(14):5240-5252
G-Protein-Dependent Facilitation of Neuronal 1A,
1B, and 1E Ca Channels
Ulises
Meza and
Brett
Adams
Department of Physiology and Biophysics, University of Iowa College
of Medicine, Iowa City, Iowa 52242-1109
Modulation of neuronal voltage-gated Ca channels has important
implications for synaptic function. To investigate the mechanisms of Ca
channel modulation, we compared the G-protein-dependent facilitation of
three neuronal Ca channels. 1A,
1B, or 1E subunits were
transiently coexpressed with 2- b and
3 subunits in HEK293 cells, and whole-cell currents were
recorded. After intracellular dialysis with GTP S, strongly
depolarized conditioning pulses facilitated currents mediated by each
Ca channel type. The magnitude of facilitation depended on current
density, with low-density currents being most strongly facilitated and
high-density currents often lacking facilitation. Facilitating
depolarizations speeded channel activation ~1.7-fold for
1A and 1B and increased current amplitudes by the same proportion, demonstrating equivalent
facilitation of G-protein-inhibited 1A and
1B channels. Inactivation typically obscured
facilitation of 1E current amplitudes, but the
activation kinetics of 1E currents showed consistent and
pronounced G-protein-dependent facilitation. The onset and decay of
facilitation had the same kinetics for 1A,
1B, and 1E, suggesting that
G dimers dissociate from and reassociate with these Ca channels
at very similar rates. To investigate the structural basis for N-type
Ca channel modulation, we expressed a mutant of 1B
missing large segments of the II-III loop and C terminus. This
deletion mutant exhibited undiminished G-protein-dependent
facilitation, demonstrating that a G interaction site recently
identified within the C terminus of 1E is not required for modulation of 1B.
Key words:
Ca channel modulation; neuronal Ca channels; membrane-delimited pathway; G-protein-dependent Ca channel inhibition; presynaptic inhibition; signal transduction; neuronal integration; neuronal plasticity; molecular neuroscience; facilitation; 1A; 1B; 1C; 1E; neurosecretion; electrical excitability
Copyright © 1998 Society for Neuroscience 0270-6474/98/18145240-13$05.00/0
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