Functional properties of a neuronal class C L-type calcium channel.
The rat brain class C calcium channel alpha 1 subunit cDNA, rbC-II, was subcloned into a vertebrate expression vector and transient expression was assayed following nuclear injection into Xenopus oocytes. Whole cell recordings showed that rbC-II currents (recorded with 40 mM Ba2+ as the charge carrier) had variable activation rates and minimal inactivation over an approximately 700 msec depolarizing step pulse. The pharmacological properties of the rbC-II current were consistent with those of an L-type calcium channel, being sensitive to dihydropyridines (10 microM nifedipine blocked approximately 85% of the current, 10 microM Bay K 8644 enhanced the current between 2- and 10-fold) and not affected by the N- and P-type calcium channel antagonists, omega-conotoxin GVIA and omega-agatoxin IVA, respectively. Coexpression of rbC-II with cloned rat neuronal calcium channel alpha 2 and beta subunits resulted in several changes to the electrophysiological properties of the rbC-II current including, an increased whole cell peak current, an increased rate of activation and a hyperpolarizing shift in the voltage dependence of activation. Taken together with results showing that the neuronal class D alpha 1 subunit also encodes an L-type calcium channel [Williams M. E., Feldman D. H., McCue A. F., Brenner R., Velicelebi G., Ellis S. B. and Harpold M. M. (1992a) Neuron 8: 71-84], these results indicate that the mammalian nervous system expresses two distinct genes encoding L-type calcium channels.
Tomlinson
W J
WJ
Biotechnology Laboratory, University of British Columbia, Vancouver, Canada.
Stea
A
A
Bourinet
E
E
Charnet
P
P
Nargeot
J
J
Snutch
T P
TP
D000818:Animals; D001923:Brain Chemistry; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005260:Female; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D010957:Plasmids; D051381:Rats; D014982:Xenopus laevis
D002121:Calcium Channel Blockers; D015220:Calcium Channels