h-89 and anandamide

The activity of the transient receptor potential vanilloid type 1 ion channel (TRPV1) that is expressed by the great majority of polymodal nociceptors is pivotal for the development of inflammatory heat hyperalgesia. The responsiveness of TRPV1 is regulated by a series of intracellular signalling molecules including the cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA); increased or decreased PKA activity results in TRPV1 sensitisation or desensitisation, respectively. Activation of the cannabinoid 1 (CB1) receptor that is expressed by the majority of the TRPV1-expressing primary sensory neurons reduces PKA activity. Therefore, here we studied whether activation of the CB1 receptor resulted in reduced TRPV1-mediated responses in cultured rat primary sensory neurons. We found that TRPV1-mediated whole-cell currents were significantly reduced respectively, by 50% and 25% by 10 nM and 30 nM of the endogenous CB1 receptor agonist, anandamide. The PKA inhibitor, H89 (10 microM) also had a significant inhibitory effect on TRPV1-mediated currents ( approximately 70%). These findings suggest that activation of the CB1 receptor can reduce the activity of TRPV1 in primary sensory neurons, and that this inhibitory effect could be mediated through the reduction of PKA-mediated phosphorylation of TRPV1.

Topics: Animals; Arachidonic Acids; Cannabinoid Receptor Modulators; Capsaicin; Cells, Cultured; Cyclic AMP-Dependent Protein Kinases; Endocannabinoids; Evoked Potentials; Female; Ganglia, Spinal; Isoquinolines; Patch-Clamp Techniques; Phosphorylation; Polyunsaturated Alkamides; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; Receptor, Cannabinoid, CB1; Sensory Receptor Cells; Sensory System Agents; Sulfonamides; TRPV Cation Channels

At birth, the increase in oxygen causes contraction of the ductus arteriosus, thus diverting blood flow to the lungs. Although this contraction is modulated by substances such as endothelin and dilator prostaglandins, normoxic contraction is an intrinsic property of ductus smooth muscle. Normoxic inhibition of potassium channels causes membrane depolarization and calcium entry through L-type calcium channels. However, the studies reported here show that after inhibition of this pathway there is still substantial normoxic contraction, indicating the involvement of additional mechanisms.. Using ductus ring experiments, calcium imaging, reverse-transcription polymerase chain reaction, Western blot, and cellular electrophysiology, we find that this depolarization-independent contraction is caused by release of calcium from the IP3-sensitive store in the sarcoplasmic reticulum, by subsequent calcium entry through store-operated channels, and by increased calcium sensitization of actin-myosin filaments, involving Rho-kinase.. Much of the normoxic contraction of the ductus arteriosus at birth is related to calcium entry through store-operated channels, encoded by the transient receptor potential superfamily of genes, and to increased calcium sensitization. A clearer understanding of the mechanisms involved in normoxic contraction of the ductus will permit the development of better therapy to close the patent ductus arteriosus, which constitutes approximately 10% of all congenital heart disease and is especially common in premature infants.

Topics: Animals; Arachidonic Acids; Boron Compounds; Calcium; Calcium Channel Blockers; Calcium Channels, L-Type; Calcium Signaling; Cytosol; Ductus Arteriosus; Endocannabinoids; Imidazoles; In Vitro Techniques; Indoles; Intracellular Signaling Peptides and Proteins; Isoquinolines; Maleimides; Menthol; Mibefradil; Muscle Contraction; Nifedipine; Niflumic Acid; Oxidation-Reduction; Oxygen; Patch-Clamp Techniques; Polyunsaturated Alkamides; Potassium Channels; Protein Serine-Threonine Kinases; Rabbits; rho-Associated Kinases; Ruthenium Red; Sulfonamides; Tetraethylammonium; Thapsigargin; Thiourea