Cyclic GMP regulates activation of phosphoinositidase C by bradykinin in sensory neurons.

Prior exposure of cultured neonatal rat dorsal root ganglion (DRG) neurons to bradykinin resulted in marked attenuation of bradykinin-induced activation of phosphoinositidase C (PIC). The (logconcentration)-response curve for bradykinin-induced [3H]inositol trisphosphate ([3H]IP3) formation was shifted to the right and the maximum response was reduced. Bradykinin increases cyclic GMP (cGMP) in DRG neurons [Burgess, Mullaney, McNeill, Coote, Minhas and Wood (1989) J. Neurochem. 53, 1212-1218] and treatment of the neurons with dibutyryl cGMP (dbcGMP) had a similar, inhibitory, effect on bradykinin-induced [3H]IP3 formation. NG-Nitro-L-arginine (LNNA) blocked bradykinin-induced formation of cGMP. It prevented the functional uncoupling induced by pretreatment with bradykinin, but not the inhibitory effect of dbcGMP on [3H]IP3 formation. The ability of LNNA to prevent desensitization was reversed by excess L-arginine, indicating that its actions were mediated through inhibition of nitric oxide synthase. In addition to functional desensitization, exposure to bradykinin reduced the number of cell-surface receptors detected with [3H]bradykinin, without affecting its KD value for the remaining sites. In contrast to bradykinin, pretreatment with dbcGMP had no effect on either the KD or B(max) for [3H]bradykinin binding. This implies that the inhibitory effect of dbcGMP was down-stream from the binding of bradykinin to its receptor and upstream of IP3 formation. The lack of effect of dbcGMP on [3H]bradykinin binding suggests that the decrease in receptor number induced by bradykinin was mediated by a different mechanism and was not a key factor in the rapid phase of desensitization in these cells.