| Summary: | An in vitro technique for perfusion of the intestinal vasculature and lumen was developed and used to measure calcium (Ca2+) fluxes across the intestinal mucosa of the marine teleost, the Atlantic cod ( Gadus morhua ). Saturable and nonsaturable components of the calcium influx and efflux were determined. The calcium influx had one passive component and one saturable component, following Michaelis-Menten kinetics with K m = 8.41mmoll-1 and V max = 0.604µmol Ca2+ kg-1 h-1. At physiological Ca2+ concentrations in the vascular ([Ca2+] = l.9mmoll-1) and luminal ([Ca2+] =14.9mmoll-1) perfusion fluids, the saturable component amounted to 60% of the Ca2+ influx. The high-affinity Ca2+-ATPase inhibitor chlorpromazine (CP, 10-4moll-1) antagonized 45% of the Ca2+ influx. The Ca2+ efflux across the intestinal mucosa of the cod was a saturable process, following Michaelis-Menten kinetics with K m =6.15mmoll-1 and V max =3.79µmol Ca2+ kg-1h-1, but insensitive to CP (l0-5moll-1) . The Ca2+ efflux was l.22µumol Ca2+ kg-1 h-1, representing about 20% of the total calcium excretion and about 50% of the extrarenal excretion of the Atlantic cod in vivo .
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