Inhibition of the interaction of G protein G(o) with calcium channels by the calcium channel beta-subunit in rat neurones.
1. The beta-subunit has marked effects on the biophysical and pharmacological properties of voltage-dependent calcium channels. In the present study we examined the ability of the GABAB agonist (-) -baclofen to inhibit calcium channel currents in cultured rat dorsal root ganglion neurones following depletion of beta-subunit immunoreactivity, 108-116 h after microinjection of a beta-subunit antisense oligonucleotide. 2.We observed that, although the calcium channel current was markedly reduced in amplitude following beta-subunit depletion, the residual current (comprising both N- and L-type calcium channel currents) showed an enhanced response to application of (-) -baclofen. Therefore, it is possible that there is normally competition between activated G protein G(o) and the calcium channel beta-subunit for binding to the calcium channel alpha 1-subunit; and this competition shifts in favour of the binding of activated G(o) following depletion of the beta-subunit, resulting in increased inhibition. 3. This hypothesis is supported by evidence that an antibody against the calcium channel beta-subunit completely abolishes stimulation of the GTPase activity of G(o) by the dihydropyridine agonist S-(-) -Bay K 8644 in brain membranes. This stimulation of GTPase is thought to result from an interaction of G(o) alpha-subunit (G alpha o) with its calcium channel effector which may operate as a GTPase-activating protein. 4. These data suggest that the calcium channel beta-subunit when complexed with the beta 1-subunit normally inhibits its association with activated G(o). It may function as a GTPase-activating protein to reduce the ability of activated G(o) to associate with the calcium channel, and thus limit the efficacy of agonists such as (-) -baclofen.
Campbell
V
V
Department of Pharmacology, Royal Free Hospital School of Medicine, London, UK.
Berrow
N S
NS
Fitzgerald
E M
EM
Brickley
K
K
Dolphin
A C
AC
D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D001418:Baclofen / Q000494:pharmacology; D001483:Base Sequence; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D004594:Electrophysiology; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D051381:Rats
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D016376:Oligonucleotides, Antisense; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D001418:Baclofen