Calcium channel beta subunits differentially regulate the inhibition of N-type channels by individual Gbeta isoforms.
The direct inhibition of N- and P/Q-type calcium channels by G protein betagamma subunits is considered a key mechanism for regulating presynaptic calcium levels. We have recently reported that a number of features associated with this G protein inhibition are dependent on the G protein beta subunit isoform (Arnot, M. I., Stotz, S. C., Jarvis, S. E., Zamponi, G. W. (2000) J. Physiol. (Lond.) 527, 203-212; Cooper, C. B., Arnot, M. I., Feng, Z.-P., Jarvis, S. E., Hamid, J., Zamponi, G. W. (2000) J. Biol. Chem. 275, 40777-40781). Here, we have examined the abilities of different types of ancillary calcium channel beta subunits to modulate the inhibition of alpha(1B) N-type calcium channels by the five known different Gbeta subunit subtypes. Our data reveal that the degree of inhibition by a particular Gbeta subunit is strongly dependent on the specific calcium channel beta subunit, with N-type channels containing the beta(4) subunit being less susceptible to Gbetagamma-induced inhibition. The calcium channel beta(2a) subunit uniquely slows the kinetics of recovery from G protein inhibition, in addition to mediating a dramatic enhancement of the G protein-induced kinetic slowing. For Gbeta(3)-mediated inhibition, the latter effect is reduced following site-directed mutagenesis of two palmitoylation sites in the beta(2a) N-terminal region, suggesting that the unique membrane tethering of this subunit serves to modulate G protein inhibition of N-type calcium channels. Taken together, our data suggest that the nature of the calcium channel beta subunit present is an important determinant of G protein inhibition of N-type channels, thereby providing a possible mechanism by which the cellular/subcellular expression pattern of the four calcium channel beta subunits may regulate the G protein sensitivity of N-type channels expressed at different loci throughout the brain and possibly within a neuron.
Feng
Z P
ZP
Department of Physiology, University of Calgary, Calgary T2N 4N1, Canada.
Arnot
M I
MI
Doering
C J
CJ
Zamponi
G W
GW
D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D049452:Green Fluorescent Proteins; D006801:Humans; D007700:Kinetics; D008164:Luminescent Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D016297:Mutagenesis, Site-Directed; D009474:Neurons / Q000378:metabolism; D019308:Palmitic Acid / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
C096073:CACNB3 protein, human; C107598:CACNB4 protein, human; C484333:Cacnb3 protein, rat; C491529:Cacnb4 protein, rat; D015220:Calcium Channels; D008164:Luminescent Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D019308:Palmitic Acid