Microscale Heat Transfer Transduced by Surface Plasmon Resonant Gold Nanoparticles.

Visible radiation at resonant frequencies is transduced to thermal energy by surface plasmons on gold nanoparticles. Temperature in

GABA(C) receptors in neuroendocrine gut cells: a new GABA-binding site in the gut.

Although GABA(C) receptors play a crucial role in the mammalian central nervous system, their functional expression in peripheral tissues has not yet been studied. Using the gut neuroendocrine tumor cell line STC-1 as a model, we provide first evidence for the functional expression of GABA(C) receptors in the gut: mRNAs of the GABA(C) receptor subunits rho1 and rho2 were detected in STC-1 cells by reverse transcription polymerase chain reaction (RT-PCR). Applying anti-rho-antibodies, specific immunostaining for GABA(C) receptors was observed. For functional characterization, the effects of GABA(C) receptor activation on [Ca2+]i and hormone secretion were studied. The selective GABA(C) receptor agonist cis-4-aminocrotonic acid (CACA) induced dose-dependent increases both of [Ca2+]i and of hormone (cholecystokinin) secretion. The stimulatory effects of CACA were antagonized by the GABA(C) receptor blockers (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) and 3-aminopropyl(methyl)phosphinic acid (3-APMPA). These results demonstrate that GABA(C) receptors play an important role in neuroendocrine gastrointestinal secretion.

Pacing the canine ileostomy.

The aim of this study was to determine whether retrograde electric pacing of a 50 cm isoperistaltic duodenal segment transposed to a location 30 cm proximal to the stoma would provide continence and improve absorption in dogs with incontinent ileostomies. In five ileostomy dogs with transposed duodenal segments, electrodes were applied to the segments for monitoring electric activity and for pacing the segments in a backward or orad direction at will. After recovery, each of the fasted, conscious dogs underwent four control and four pacing experiments during which ileostomy output and enteric transit and absorption were monitored for 9 hours after a meal of 200 gm of technetium-99m-labeled liver and 50 ml of polyethylene glycol-labeled water. In pacing experiments the pacesetter potentials of the transposed segment were driven backward by pacing during the first 3 postcibal hours. Pacing markedly slowed gastrointestinal transit of both liquid and solid and decreased output from the stoma during the pacing period, thus changing an incontinent ileostomy into a more continent one. Output was only 9 +/- 3 ml/hr (mean +/- SEM) during pacing, compared with 19 +/- 3 ml/hr without pacing (p = 0.01). Pacing, however, did not improve overall enteric absorption after the meal. In conclusion, pacing a duodenal segment transposed to a preileostomy location slowed intestinal transit and converted an incontinent ileostomy into a more continent one, but it did not improve overall intestinal absorption.

Short-chain fatty acids stimulate motility of the canine ileum.

Based on earlier observations that colonic contents stimulated ileal motility in the dog, our hypothesis is that the ileum would respond to physiological amounts of short-chain fatty acids (SCFA). Four dogs had isolated ileocolonic loops constructed surgically and boluses of test solutions (15 ml) were instilled into the distal ileum through a small catheter. Intraluminal pressure catheters were used to record motility. Concentrations of SCFA (also called volatile fatty acids) comparable to those found in dog stool (108 mM; 66% acetic, 24% propionic, and 10% butyric acids) regularly stimulated motility with a dose-related effect. The response was not due to the pH of the SCFA solutions and was independent of the pH at which SCFA were instilled. Ricinoleic acid (4 mM) also stimulated motility, as did chenodeoxycholic acid; the bile acid was active only at supraphysiological concentrations (approximately 7.6 mM). Instillates that simulated the composition of ileal chyme in malabsorptive states were without effect. The results suggest that the ileum can "sense" the presence of colonic contents in the lumen and that SCFA are the responsible mechanisms. Stimulation of ileal motility by SCFA could be a response to coloileal reflux.