Protein kinase C contributes to abnormal capsaicin responses in DRG neurons from cats with feline interstitial cystitis

Abstract

Interstitial cystitis (IC) is a painful disorder which affects urinary bladder function in cats and humans. We have used patch clamp techniques to examine the possibility that the properties of primary afferent neurons are changed in feline interstitial cystitis (FIC). We measured transient receptor potential vanilloid receptor 1 (TRPV1) responses to capsaicin (CAPS) in dorsal root ganglion (DRG) neurons (L4-S3) from normal cats and cats with FIC. We show that FIC neurons are increased in size and exhibit CAPS responses which are increased in amplitude and desensitize slowly. CAPS responses desensitized seven times slower in FIC neurons. Phorbol 12,13-dibutyrate (PDBu), an activator of PKC, slowed the desensitization of CAPS responses in normal cat bladder and nonbladder neurons, but had no effect in FIC neurons. Bisindolylmaleimide, an inhibitor of PKC, reversed the PDBu effects in normal cat neurons and normalized the desensitization of CAPS responses in FIC neurons. Our data suggest that FIC afferent neurons exhibit abnormal CAPS responses. The latter may be due to enhanced endogenous activities of PKC. KeywordsDorsal root ganglia; Capsaicin; Nociception; Transient receptor potential vanilloid receptor 1; Protein kinase C; Phosphorylation; Desensitization; Interstitial cystitis; Diaryl piperazine Interstitial cystitis (IC) is a chronic pelvic pain syndrome of humans [2,8,14]. A comparable disorder, feline interstitial cystitis (FIC), has been identified in domestic cats [3,4]. Previous studies revealed an increased density of peptidergic afferent nerves in the bladders of FIC cats suggesting that an abnormality of afferent pathways might contribute to the disorder [5,12].Bladder pain and hyperactivity can be induced by activation of capsaicin (CAPS)-sensitive, unmyelinated (C-type) afferent nerves [7,18,20]. Intravesical administration of CAPS induces bladder pain; whereas desensitization of C-fiber bladder afferents with intravesical administration of resiniferatoxin, an ultrapotent CAPS analog, has been reported to reduce bladder overactivity [18]. The CAPS sensitivity of C-fiber afferent nerves is conferred by the presence of a temperature-acid sensing receptor called the transient receptor potential vanilloid receptor 1 (TRPV1) [6,10]. Protein kinase C phosphorylation of TRPV1 has been reported to sensitize the response of this receptor to agonists [1,22]. Here, we investigated the properties of primary afferent neurons in lumbo-sacral dorsal root ganglia (DRG) from normal cats and To identify FIC in cats, we utilized criteria as previously described [4]. Cells were isolated from L4-S3 DRG of cats using methods previously described for primary cultures of DRG neurons of adult rat [15]. In some experiments, the population of DRG neurons that innervate the urinary bladder was labeled by retrograde axonal transport of a fluorescent dye, fast blue (FB, 4% w/v, Polyloy, Gross Umstadt, Germany [21]). In these experiments, dye-labeled primary afferent neurons were identified using an inverted phase-contr...

Transient Receptor Potential Channels as Drug Targets: From the Science of Basic Research to the Art of Medicine

“…In a feline model of interstitial cystitis, abnormally enhanced capsaicin responses were detected (Sculptoreanu et al, 2005a) secondary to TRPV1 phosphorylation by PKC (Sculptoreanu et al, 2005b). In addition, increased TRPV1 expression was reported in bladder afferents of patients with interstitial cystitis (Mukerji et al, 2006b).…”

Neurokinins enhance excitability in capsaicin-responsive DRG neurons

“…In these neurons the membrane capacitance (pF) varied linearly as a function of average cell diameter (μM). CAPS currents were recorded in voltage clamp as previously described (Sculptoreanu et al, 2005b). Action potentials in response to current injections were recorded using an Axopatch 200A (Axon Instruments, Foster City, California) amplifier.…”

Medicinal chemistry of the vanilloid (Capsaicin) TRPV1 receptor: current knowledge and future perspectives

“…In feline interstitial cystitis, the phosphorylation state of TRPV1 appears to be disease-specific [Sculptoreanu et al, 2005]. If so, it may have important implications for drug development since the pharmacological activity of some agonist/partial antagonist compounds is affected by the phosphorylation state of TRPV1 Lizanecz et al, 2006].…”