Bradykinin‐induced activation of nociceptors: receptor and mechanistic studies on the neonatal rat spinal cord‐tail preparation in vitro

Abstract

1 The effects of bradykinin on nociceptors have been characterized on a preparation of the neonatal rat spinal cord with functionally connected tail maintained in vitro. Administration of bradykinin to the tail activated capsaicin-sensitive peripheral fibres and evoked a concentration-dependent (EC50= 130 nM) depolarization recorded from a spinal ventral root (L3-L5). 2 The response to bradykinin was unaffected by the peptidase inhibitors, bestatin (0.4 mM), thiorphan(1 gM), phosphoramidon (1 ELM) and MERGETPA (10 gM) or by the presence of calcium blocking agents, cadmium (200 gM) and nifedipine (10 4M).3 Inhibition of cyclo-oxygenase with indomethacin (1-5I1M), aspirin (1-1O M) and paracetamol (10-50ILM) consistently attenuated responses to bradykinin. 4 The effect of bradykinin was mimicked by the phorbol ester PDBu, an activator of protein kinase C. The response to bradykinin was attenuated following desensitization to PDBu but desensitization to bradykinin did not induce a cross-desensitization to PDBu. The protein kinase C inhibitor staurosporine (10-500 nM) consistently attenuated the effects of PDBu and bradykinin.5 Bradykinin responses were reversibly enhanced by dibutyryl cyclic AMP (100 gM). However dibutyryl cyclic GMP (0.5 mM) and nitroprusside (10 EM) produced prolonged block of responsiveness to bradykinin. Prolonged superfusion with pertussis toxin did not affect responses to bradykinin. 6 The B,-receptor agonist des Arg9-bradykinin (10-100 AM) was ineffective alone or after prolonged exposure of the tail to lipopolysaccharide (100 ng ml-') or epidermal growth factor (100 ng ml-') to induce B, receptors. The BI-receptor antagonist, des Arg9 Leu8-bradykinin (10 JM 7 These data show that bradykinin produces concentration-dependent activation of peripheral nociceptors in the neonatal rat tail. The responses were unaffected by calcium channel block and were partially dependent on the production of prostanoids. Bradykinin-evoked responses were consistent with the activation of protein kinase C-dependent mechanisms. Cyclic GMP-dependent mechanisms may be involved in bradykinin-receptor desensitization whereas cyclic-AMP dependent mechanisms increase fibre excitability and facilitate bradykinin-induced responses. The effects of bradykinin were mediated by a B2 receptor.

Sensory and Signaling Mechanisms of Bradykinin, Eicosanoids, Platelet-Activating Factor, and Nitric Oxide in Peripheral Nociceptors

“…A depolarizing effect of bradykinin on somata of rabbit nodose, i.e., vagal, ganglion neurons was observed 30 years ago (277 tured rat DRG neurons was shown to be mediated by a pertussis toxin-insensitive G protein (76,(482)(483)(484)719), and a similar result was obtained in the neonatal rat spinal cord-tail preparation in vitro in which the excitatory effect of bradykinin applied to the tail was recorded as a reflex depolarization of the ventral root (162). This G protein was subsequently identified as a G q/11 activating PLC (254).…”

“…Downregulation of PKC strongly reduced bradykinin-induced release of SP and CGRP from cultured rat sensory neurons (42). Phorbol esters, which activate PKC, mimicked most effects of bradykinin in the experimental models mentioned above (42,76,162). The involvement of PKC in the bradykinin-induced PGE 2 release from cultured rat trigeminal neurons was also established (315).…”

“…Early studies provided indirect evidence showing that staurosporine, an inhibitor of protein kinases, attenuated the depolarizing effect of bradykinin in the neonatal rat spinal cord-tail preparation in vitro (160,162) and also in cultured DRG neurons (76,483). Downregulation of PKC strongly reduced bradykinin-induced release of SP and CGRP from cultured rat sensory neurons (42).…”

Involvement of B1 and B2 receptors in bradykinin‐induced rat paw oedema

“…In addition, prior treatment of animals with dexamethasone (0.5 mg kg-', 24 h previously) also consistently antagonized DABK (100 nmol/paw)-induced oedema in desensitized paws (53 ± 4% inhibition) (P <0.05) (Figure 9a). In contrast, the same treatment with dexamethasone had no effect on oedema induced by BK (3 nmol/paw) in naive paws (Figure 9b Similar inhibition of kinin responses in vivo by these B2 antagonists has been reported (Wirth et al, 1991;Dray et al, 1992;Correa & Calixto, 1993;Heapy et al, 1993;. It is important to mention that co-injections of different combinations of PGE2, PGI2, SP, CGRP or histamine always resulted in oedema that was smaller than that caused by any co-injections with BK.…”

The acute nociceptive signals induced by bradykinin in rat sensory neurons are mediated by inhibition of M-type K+ channels and activation of Ca2+-activated Cl– channels

“…Additional mechanisms for BK-induced hyperalgesia are mediated by PKCε (8), which in turn also causes TRPV1 sensitization (9). Unfortunately, the understanding of the molecular events underlying acute pain directly induced by BK is not that advanced and is mostly based on the electrophysiological observations of BK-induced depolarization (10,11), increased action potential (AP) firing (12), and inward current induction (10,12). BK has been referred to as "the most potent endogenous algogenic substance known" (2); thus, the elucidation of its modes and mechanisms of action should improve our ability to understand and treat spontaneous inflammatory pain.…”