APPS November 2002 Meeting Abstract 1125


PATTERN OF PACEMAKER ACTIVITY IN THE CIRCULAR AND LONGITUDINAL MUSCLE LAYERS OF THE GUINEA PIG GASTRO-DUODENAL JUNCTION

Shi-Yong Yuan, Simon J.H. Brookes, Marcello Costa, Department of Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia 5042.

External muscle of antro-duodenal regions exhibits spontaneous rhythmic contractions associated with electrical slow waves generated by the pacemaker, interstitial cells of Cajal1-3. A significant change from low frequency in the antrum to a higher frequency in the duodenum marks the gastro-duodenal junction2. We examined the variation of amplitude and frequency of the low frequency slow waves in the external muscle layers across this region. Intact antro-duodenal segments, taken from humanely killed guinea pigs were opened along the lesser curvature, pinned flat and superfused with warm oxygenated Krebs solution containing 0.6 ÁM tetrodotoxin. Slow waves were mapped by placing suction electrodes on both muscle layers in a 6 x 3 rectangular array extending from the antrum to the duodenum. Pacemaker frequency in the circular muscle in all regions varied from 5.5 ▒ 0.1 to 7.3 ▒ 0.1 /minute (n=4). In the longitudinal muscle, the frequency was less variable (range 5.3 ▒ 0.2 to 6.5 ▒ 0.1/minute), and was constant in the oral to anal direction. The pacemaker frequency in both muscle layers was slightly higher in the ventral (7.3 ▒ 0.1/minute) than dorsal (6.5 ▒ 0.2/minute) wall of the stomach. Slow waves of the circular muscle were highly variable in amplitude but were larger in the more oral region, disappearing abruptly in distal region. The amplitude of slow waves in the longitudinal muscle decreased less abruptly from the antrum to the distal pylorus. These results suggest that the circular and longitudinal muscle layers of the antro-duodenal junction are controlled by different pacemaker mechanisms.

(1) Dickens EJ, Hirst GDS, Tomita I. Journal of Physiology. 1999;514(2):515-531.

(2) Yuan SY, Costa M, Brookes SJH. Neurogastroenterological Motility. 2001;13:187-198.

(3) Hirst GDS, Beckett EAH, Sanders KM, Ward SM. Journal of Physiology. 2002;540(3):1003-1012.


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