A beta-subunit normalizes the electrophysiological properties of a cloned N-type Ca2+ channel alpha 1-subunit.
The electrophysiological and pharmacological properties of a cloned rat brain N-type Ca2+ channel were determined by transient expression in Xenopus oocytes. Expression of the class B Ca2+ channel alpha 1 subunit, rbB-I, resulted in a high voltage-threshold current that activated slowly and showed little inactivation over 800 msec. Characteristic of N-type currents, the rbB-I current was completely blocked by omega-conotoxin GVIA and was insensitive to nifedipine and Bay K8644. The modulatory effects on the rbB-I current by cloned rat brain Ca2+ channel alpha 2 and beta 1b subunits were also examined. Coexpression of rbB-I with the beta 1b subunit caused significant changes in the properties of the rbB-I current making it more similar to N-type currents in neurons. These included: (1) an increase in the whole-cell current, (2) an increased rate of activation, (3) a shift of the voltage-dependence of inactivation to hyperpolarized potentials and (4) a pronounced inactivation of the current over 800 msec. Coexpression with the rat brain alpha 2 subunit had no significant effect on the rbB-I current alone but appeared to potentiate the rbB-I+beta 1b whole cell current. The results show that coexpression with the brain beta 1b subunit normalizes the rbB-I N-type current, and suggests the possibility that differences in subunit composition may contribute to the heterogeneous properties described for N-type channels in neurons.
Stea
A
A
Biotechnology Laboratory, University of British Columbia, Vancouver, Canada.
Dubel
S J
SJ
Pragnell
M
M
Leonard
J P
JP
Campbell
K P
KP
Snutch
T P
TP
D000818:Animals; D001923:Brain Chemistry; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014981:Xenopus; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018076:DNA, Complementary; D010455:Peptides; D011994:Recombinant Proteins; D020866:omega-Conotoxin GVIA