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 Km = 8.41mmoll−1 and Vmax = 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 Km =6.15mmoll−1 and Vmax =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.