THREE DISTINCT G PROTEIN PATHWAYS MEDIATE INHIBITION OF NEURONAL CALCIUM CURRENT BY BRADYKININ. Wilk-Blaszczak, M. A., W. D. Singer, and F. Belardetti. Dept. Pharmacology, University of Texas, Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235.
APStracts 3:0158N, 1996.
SUMMARY AND CONCLUSIONS
1. In NG108-15 cells dialyzed with 10 mM EGTA or BAPTA, bradykinin (BK) selectively inhibited the N-type calcium current. This effect of BK was blocked by an antibody directed against the G protein G 13 . Thus, under these conditions G 13 mediates the inhibition of I Ca,V by BK. In contrast, activation of K + currents by BK is mediated by G q/11 . BK also couples to G i2 . 2. We have now examined the involvement of G proteins in the inhibition of I Ca,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-G 13 antibody did not suppress the response to BK. Applications of either anti-G q/11 antibody or pertussis toxin (PTX, to block G i2 ) were similarly ineffective. Even combined application of anti-G q/11 and -G 13 antibodies, or PTX together with either antibody, did not block inhibition of I Ca,V by BK. However, the combination of both antibodies with PTX blocked the response to BK in low BAPTA. In conclusion, both G q/11 and a PTX-sensitive G protein (presumably G i2 ), together with G 13 , are involved in the inhibition of I Ca,V by BK. 3. G q/11 inhibited only the L-type calcium current, while the PTX-sensitive G protein inhibited both the N- and L-type calcium currents. 4. The BAPTA-dependence of the G q/11 and PTX-sensitive inhibitions may reflect a Ca 2+ requirement of the pathway(s) acting on the L-current, and/or a direct suppressive effect of BAPTA.

Received 6 May 1996; accepted in final form 26 July 1996.
APS Manuscript Number J367-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996