Siroos S. Shirazi

Human Ileal Ion Transport In Vitro: Changes With Electrical Field Stimulation and Tetrodotoxin

To determine whether or not nerves lying in the lamina propria and submucosa affect ion transport by the human intestine, we studied the effects of electrical field stimulation on ion transport across the isolated ileum stripped of muscularis propria. Electrical field stimulation increased transmural electrical potential difference and the short-circuit current, and by increasing the serosal to mucosal movement of chloride (JsmCl), reduced the absorption of Cl (JnetCl). The movement of sodium and the residual ion movement (JnetR) were not affected. The neurotoxin, tetrodotoxin prevented all of the changes caused by electrical field stimulation, but did not prevent the responses to aminophylline, implying that tetrodotoxin affected electrically excitable cells rather than epithelial cells. Aminophylline increased the potential difference and shortcircuit current, reduced tissue conductance (G), and eliminated chloride absorption. In tissues treated with tetrodotoxin, aminophylline also reduced JmsNa, JnetNa, and JnetR; while increasing JsmCl, it augmented the reduction in JmsCl and caused chloride secretion. Atropine reduced baseline short-circuit current and reduced the short-circuit current response to electrical field stimulation. It was concluded that acetylcholine and other chemical transmitters that affect ion transport are released in the submucosa or lamina propria of the human ileum. The identity of the noncholinergic transmitters and the sequence of events leading to their liberation remain to be determined.

Neuromuscular Differentiation of the Human Pylorus

The mechanical activity of muscle strips from the gastroduodenal junction as obtained at operations was studied. Strips were cut so as to present the activity of the circular muscle layer of the antrum, the duodenum, the intermediate, or the distal pyloric sphincter. All strips increased and maintained a tension with increasing length, but distal sphincter strips did more so than the other types of strips. Phasic contractions were rare in distal sphincter strips, while all intermediate sphincter strips contracted at rates similar to antral strips. Electric field stimulation produced pure contractions in all responsive strips of the antrum and the intermediate sphincter. In most strips from the duodenum and distal sphincter the contraction response occurred during the stimulus, and the relaxation response far outlasted the stimulus. Distal sphincter strips had the larger relaxation responses, and duodenal strips had the larger contraction responses. Relaxation in response to electric stimulation, Ca++ withdrawal, or isoproterenol did not completely abolish the baseline tension of the distal sphincter. At least in its distal segment, muscle from the human pylorus differs from muscle of the antrum and the duodenum by its high baseline tension, its prominent neurogenic relaxation response, and its poor spontaneous contractile activity.

Dynamic imaging of obstructed opossum esophagus : from altered load to altered contractility

We studied by barium contrast the dynamics of experimental obstruction in the opossum esophagus. Immediately after banding the gastroesophageal junction, entrapment of the bolus between the band and the peristaltic contraction led to esophageal bulging, forceful retropulsion of the bolus at the band, and the repeated triggering of peristaltic contractions by the retropelled bolus. In ensuing weeks, triggering of contractions became more difficult and contractions led to bizarre “corkscrew” movements of the increasingly distended and tortuous esophagus. A tight contraction ring that moved very slowly retrograde was occasionally observed in the chronically distended esophagus. Computer-assisted analysis showed that the area and perimeter of the bolus were abnormally large in chronic obstruction and that during its passage through the esophagus the compactness of the bolus increased no longer. Configurational analysis of the cone that the peristaltic contraction shapes at the tail of the barium column showed this to narrow progressively on passage through the normal esophagus and, paradoxically, to widen in both acute and chronic obstruction.

Cecum of guinea pig is a reservoir and sigmoid is a high-resistance conduit

We compared the filling responses of the cecum and the sigmoid of the guinea pig using volumes up to 60 ml and 2.5 ml, respectively. In the isolated cecum, each 1-cm increment of hydrostatic pressure above zero led to accommodation of 10 ml volume; in the sigmoid, the yield pressure (at which accommodation first occurred) was 6 cm H2O, and pressure increments up to 20 cm H2O produced volume increments of less than 0.5 ml. Resting pressure at half-maximal filling was 5.0±0.7 cm H2O for the sigmoid and 1.7±0.6 cm H2O for the cecum. K+ depolarization led to a significant upward shift in the pressure curves of both segments. Ca2+ withdrawal decreased sigmoid and cecal pressures at some volumes. Distension of the cecum triggered intermittent contractions, which began with the shortening of the teniae and were associated with low-amplitude pressures and expulsion of a 5- to 10-ml volume. Distension of the sigmoid produced propagating contractions that were associated with high-amplitude pressures and lengthening; compartmentalization in the sigmoid prevented efflux from it, and volume inflow was not affected by pressure waves. Our observations indicate that its large capacity and great distensibility make the cecum suitable for reservoir functions, whereas its narrowness and lack of distensibility make the sigmoid a high-resistance conduit.