Ion transport and enteric nervous system (ENS) in rat rectal colon: mechanical stretch causes electrogenic Cl-secretion via plexus Meissner and amiloride-sensitive electrogenic Na-absorption is not affected by intramural neurons.

The initial phase of in vitro experiments in Ussing-type chambers on large intestine is characterized by short-circuit currents (ISC) declining from high starting values to a lower plateau within 0.5 h. The origin of this "initial ISC-transient" was investigated by ISC measurements on partially stripped segments of rat rectal colon. Transport was pre-stimulated in vivo by keeping animals in barbiturate-anesthesia for 5 h prior to tissue preparation. This procedure caused by endogenous aldosterone-liberation amiloride-sensitive Na-absorption to become the predominant electrogenic transport. The initial ISC-transient was abolished by tetrodotoxin (TTX, 1 microM), indicating a neuronal mediation of this phenomenon. In order to identify the transport which was subject to neuronal control, the amiloride-sensitive Na-absorption was measured during electrical field stimulation (bipolar rectangular pulses: 5 Hz, 1 ms, +/- 6 mA). There was no difference to unstimulated controls. In contrast, the initial ISC-transient was dependent on Cl in the bath following Michaelis-Menten-kinetics (KM = 20 mM) and could be prevented by 10 microM serosal bumetanide. Then, initial filling of the Ussing-chamber was imitated during the course of the experiment by removal and immediate re-addition of the bathing fluid. This procedure caused ISC-changes of similar appearance as the initial ISC-transient. To verify that indeed mechanical stretch is the sensory stimulus triggering the initial ISC-transient, the effect of small pressure oscillations was studied. This also produced an ISC-transient which was TTX-sensitive and was abolished after removal of the submucosal plexus Meissner by total stripping.(ABSTRACT TRUNCATED AT 250 WORDS)