Bradykinin, but not muscarinic, inhibition of M-current in rat sympatheticganglion neurons involves phospholipase C-beta 4

Rat superior cervical ganglion (SCG) neurons express low-threshold noninact ivating M-type potassium channels (I-K(M)), which can be inhibited by activ ation of M-1 muscarinic receptors (M-1 mAChR) and bradykinin (BK) B-2 recep tors. Inhibition by the M1 mAChR agonist oxotremorine methiodide (Oxo-M) is mediated, at least in part, by the pertussis toxin-insensitive G-protein G alpha (q) (Caulfield et al., 1994; Haley et al., 1998a), whereas BK inhibi tion involves G alpha (q) and/or G alpha (11) (Jones et al., 1995). G alpha (q) and G alpha (11) can stimulate phospholipase C-beta (PLC-beta), raisin g the possibility that PLC is involved in I-K(M) inhibition by Oxo-M and BK . RT-PCR and antibody staining confirmed the presence of PLC-beta1, - beta2 , - beta3, and - beta4 in rat SCG. We have tested the role of two PLC isofo rms (PLC-beta1 and PLC-beta4) using antisense-expression constructs. Antise nse constructs, consisting of the cytomegalovirus promoter driving antisens e cRNA corresponding to the 3'-untranslated regions of PLC-beta1 and PLC-be ta4, were injected into the nucleus of dissociated SCG neurons. Injected ce lls showed reduced antibody staining for the relevant PLC-beta isoform when compared to uninjected cells 48 hr later. BK inhibition of I-K(M) was sign ificantly reduced 48 hr after injection of the PLC-beta4, but not the PLC-b eta1, antisense-encoding plasmid. Neither PLC-beta antisense altered M-1 mA ChR inhibition by Oxo-M. These data support the conclusion of Cruzblanca et al. (1998) that BK, but not M-1 mAChR, inhibition of I-K(M) involves PLC a nd extends this finding by indicating that PLC-beta4 is involved.