Three distinct G protein pathways mediate inhibition of neuronal calcium current by bradykinin.
1. In NG108-15 cells dialyzed with 10 mM ethylene glycolbis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or bis (o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA), bradykinin (BK) selectively inhibited the N-type calcium current. This effect of BK was blocked by an antibody directed against the G protein G13. Thus under these conditions G13 mediates the inhibition of voltage-dependent calcium current (ICa, V) by BK. In contrast, activation of K+ currents by BK is mediated by Gq/11. BK also couples to Gi2. 2. We now examine the involvement of G proteins in the inhibition of ICa, V by BK when NG108-15 cells are dialyzed with 1 mM BAPTA. Under these conditions, BK inhibited both the N- and L-type, but not the T-type, calcium currents. Intracellular application of anti-G13 antibody did not suppress the response to BK. Applications of either anti-Gq/11 antibody or pertussis toxin (PTX, to block Gi2) were similarly ineffective. Even combined application of anti-Gq/11 and -G13 antibodies, or PTX together with either antibody, did not block inhibition of ICa, V by BK. However, the combination of both antibodies with PTX blocked the response to BK in low BAPTA. In conclusion, both Gq/11 and a PTX-sensitive G protein (presumably Gi2), together with G13, are involved in the inhibition of ICa, V by BK. 3. Gq/11 inhibited only the L-type calcium current, whereas the PTX-sensitive G protein inhibited both the N- and L-type calcium currents. 4. The BAPTA dependence of the Gq/11 and PTX-sensitive inhibitions may reflect a Ca2+ requirement of the pathway(s) acting on the L current and/or a direct suppressive effect of BAPTA.
Wilk-Blaszczak
M A
MA
Department of Pharmacology, University of Texas, Southwestern Medical Center, Dallas 75235, USA.
Singer
W D
WD
Belardetti
F
F
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000187:drug effects* / Q000378:metabolism; D011817:Rabbits
D015220:Calcium Channels; D004533:Egtazic Acid; D019204:GTP-Binding Proteins; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D001920:Bradykinin; D002118:Calcium