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The secretory action of barium chloride in rat colon.
Author(s) -
Hardcastle J,
Hardcastle P T,
Noble J M
Publication year - 1985
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1985.sp015630
Subject(s) - chemistry , ouabain , endocrinology , medicine , calcium , theophylline , secretion , acetylcholine , promethazine , sodium , pharmacology , biochemistry , biology , organic chemistry
BaCl2, applied serosally, caused a rise in the p.d. and short‐circuit current (s.c.c), and a decrease in tissue resistance in stripped sheets of rat colon. This response was dose dependent. Mucosal application of BaCl2 was without effect. The BaCl2‐induced rise in s.c.c. was inhibited by reducing the serosal Na+ concentration to 25 mM. Lowering the mucosal Na+ concentration was without effect. Ouabain (10(‐3) M in serosal fluid) and furosemide (10(‐3) M in serosal fluid) both reduced the rise in s.c.c. induced by BaCl2. Flux determinations indicated that BaCl2 inhibited Na+ absorption and stimulated Cl‐ secretion by the colon. In vivo, BaCl2 increased fluid accumulation within the colonic lumen, an effect that was associated with a rise in the transcolonic p.d. Increasing the serosal K+ concentration to 20 mM reduced the responses to BaCl2, acetylcholine and theophylline, and this could not be entirely accounted for by the concomitant reduction in the serosal Na+ concentration. As high serosal K+ did not mimic the secretory response it would appear that BaCl2 does not act by blocking K+ channels. The rise in s.c.c. induced by BaCl2 was not reduced by Ca2+‐free conditions, but it was inhibited by 8‐(N,N‐diethylamino)‐octyl‐3,4,5‐trimethoxybenzoate hydrochloride (TMB‐8) and trifluoperazine. BaCl2 did not alter cyclic AMP production by colonic scrapes. It is concluded that BaCl2 induces colonic secretion by the release of intracellular Ca2+, which then combines with calmodulin to activate the secretory process.