ABSTRACT
BACKGROUND: Serotonin (5-hydroxytryptamine [5-HT]) has been shown to induce chloride secretion through a nonadrenergic/noncholinergic neural pathway, mediated by a 5-HT(3) receptor. We hypothesized that 5-HT(3)-induced Cl(-) secretion is ultimately mediated by nitric oxide (NO). METHODS: Unstripped sheets of rat distal colon were mounted in Ussing chambers and short-circuited. The 5-HT(3) receptor agonist, 2-methyl-5-HT, was added in the absence and presence of the NO synthase inhibitor, L-NAME. Companion studies involved the addition of sodium nitroprusside to tissue that was incubated with or without tetrodotoxin. RESULTS: L-NAME caused a significant reduction in the 2-methyl-5-HT-induced change in circuit current, in a concentration-dependent manner. Sodium nitroprusside caused a change in circuit current over baseline in 5 minutes. The addition of tetrodotoxin did not significantly alter the change in circuit current; however, the apical Cl(-) channel blocker, anthracene-9-carboxylic acid, abolished this response. CONCLUSIONS: Neurally mediated Cl(-) secretion in response to 2-methyl-5-HT is inhibited by an NO synthase inhibitor. Exogenous NO mimics this response, which is unaffected by tetrodotoxin. These data suggest that neurally mediated serotoninergic Cl(-) secretion is, in part, mediated by NO. The ability of exogenous NO to induce a change in circuit current in the presence of tetrodotoxin suggests that NO is a final neurotransmitter in this neural-mucosal reflex and therefore acts directly on the enterocyte to induce secretion.
Subject(s)
Chlorides/metabolism , Colon/physiology , Intestinal Mucosa/physiology , NG-Nitroarginine Methyl Ester/pharmacology , Nitric Oxide/physiology , Receptors, Serotonin/physiology , Serotonin/physiology , Animals , In Vitro Techniques , Intestinal Mucosa/drug effects , Male , Membrane Potentials/drug effects , Membrane Potentials/physiology , Nitric Oxide Synthase/antagonists & inhibitors , Nitroprusside/pharmacology , Patch-Clamp Techniques , Rats , Rats, Sprague-Dawley , Receptors, Serotonin, 5-HT3 , Serotonin/analogs & derivatives , Serotonin/pharmacology , Tetrodotoxin/pharmacologyABSTRACT
In the pediatric cancer alveolar rhabdomyosarcoma, the common 2;13 and less frequent 1;13 translocations fuse PAX3 and PAX7, respectively, with FKHR to produce chimeric genes. To compare structural features of these rearrangements, we cloned and mapped a 64-kb genomic region containing PAX7 exons 5 through 8. With the use of Southern blot methodology, rearrangements of the 30-kb PAX7 intron 7 were detected in 9 of 9 PAX7-FKHR-positive cases. Similar to our t(2;13) studies, the t(1;13) breakpoints were randomly distributed within the seventh intron. In contrast with the > 90% frequency of reciprocal rearrangements in the t(2;13), reciprocal rearrangements involving the 3' PAX7 region were detected in only 4 of 9 cases. Furthermore, we detected PAX7-FKHR genomic amplification in 10 of 11 cases, in contrast with the < 5% frequency of PAX3-FKHR amplification. The differences in occurrence, reciprocity, and amplification between the PAX3-FKHR and PAX7-FKHR fusions indicate important differences in the mechanism of the two associated chromosomal translocation events.
