The capsaicin receptor TRPV1 is a nonselective cation channel that is expressed in sensory neurons. In this study, we examined the role of the nonreceptor cellular tyrosine kinase c-Src kinase in the modulation of the rat TRPV1. Capsaicininduced currents in identified colonic dorsal root ganglion neurons were blocked by the c-Src kinase inhibitor PP2 and enhanced by the tyrosine phosphatase inhibitor sodium orthovandate. PP2 also abolished currents in human embryonic kidney-293 cells transfected with rat TRPV1, whereas cotransfection of TRPV1 with v-Src resulted in fivefold increase in capsaicin-induced currents. In cells transfected with dominant-negative c-Src and TRPV1, capsaicin-induced currents were decreased by approximately fourfold. TRPV1 co-immunoprecipitated with Src kinase and was tyrosine phosphorylated. These studies demonstrate that TRPV1 is a potential target for cellular tyrosine kinase-dependent phosphorylation.capsaicin; pp 60 ; cation channel; immunoprecipitation; inflammatory bowel disease; pain THE VANILLOID RECEPTOR, VR1 or TRPV1, is a nonselective cation channel with homology to the transient receptor potential (TRP) family of ion channels. Expression of the TRPV1 channel in nociceptors, and its polymodal nature of activation by heat and protons, define the physiological role of this channel in pain sensation. In addition to the direct activation by capsaicin, which was originally used to characterize and clone the TRPV1 channel, both G-protein-coupled receptors (e.g., bradykinin receptor) and tyrosine kinase receptor (e.g., receptor for nerve growth factor) indirectly modulate the kinetics of the channel through pathways involving release from phosphatidylinositol 4,5-bisphosphate (PIP 2 )-mediated inhibition (5).Phosphorylation/dephosphorylation of ion channels is a major mechanism by which channel function is regulated, under both basal conditions, as well as in response to various ligands. Both protein kinases C and A have been demonstrated to regulate TRPV1 currents (1,4,8,10,14,16,18,22,31). The potential phosphorylation sites for protein kinase C⑀ were recently identified as Ser 502 and Ser 800 on TRPV1 (14). Protein kinase A phosphorylates Ser 116 of TRPV1 under basal conditions, and dephosphorylation appears to be a primary mechanism that initiates desensitization of the channel (4). There is now accumulating evidence that cellular tyrosine kinases may also play a potential role in the regulation of ion channel function. For instance, our laboratory (9, 11) and others (3,13,20,25,26,28) have previously defined a significant role for the cellular tyrosine kinase c-Src kinase in regulation of the L-type calcium channel, both under basal conditions and in response to G-protein-coupled receptors and tyrosine kinase receptors. Src-kinase-mediated regulation of store-operated channels, presumably due to TRP channels, has also been demonstrated in fibroblasts (2, 27). A direct role for Src-mediated regulation of TRPV4, a close homolog of TRPV1, was recently identified by Xu et al. (29). ...

L-Type voltage-dependent Ca2+ channels (L-VDCC) mediate calcium influx in response to membrane depolarization and regulate intracellular processes such as contraction, secretion, neurotransmission, and gene expression. Colonic inflammation significantly attenuates calcium currents in smooth muscle; however, the basis for this remains unclear. In this study we examined the protein and mRNA expression of two isoforms of Ca(v)1.2, encoded by either exon la or 1b. Both isoforms were detected by Western blots, immunohistochemistry and RT-PCR in smooth muscle cells. Neither the protein nor mRNA expression measured by real-time PCR of either isoforms was affected in colonic myocytes from dextran sulfate sodium-treated mice. In whole-cell voltage-clamp experiments, the amplitude of the calcium currents were decreased by almost 70% by inflammation. The calcium channel currents were attenuated by 50 +/- 3% by the c-src kinase specific inhibitor, PP2, in control cells but only 19 +/- 7% in cells from inflamed mice. These studies suggest that decreased calcium channel currents following colonic inflammation are not due to decreased expression but may result from altered regulation by the non-receptor cellular tyrosine kinase, c-src kinase.

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Abstract-The metabolic degradation of PGE, was studied by the incubation of ³H -PGE_I with rat and dog plasma and thoracic lymph and the homogenates of various rat and dog tissues. It was observed that rat and dog plasma metabolize very little PGE₁ even when incubated for one hr. Very little metabolic degradation of PGE₁ was found by dog thoracic lymph. In contrast, rat and dog lung and kidney metabo l ize PGE₁ very rapidly, and approx. 95% of PGE₁ was converted to a less polar metabolite within 20 min of incubation. The metabolic degradation of PGE, was also rapid in the homogenates of rat stomach and jejunum, but the velocity of this reaction in these homogenates was slower than that in the rat or dog lung and kidney homogenates.

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