Abstract
The present study reports on the effects of dopamine on sodium transepithelial transport and Na +,K +-ATPase activity in Caco-2 cells, a human epithelial intestinal cell line which undergoes enterocyte differentiation in culture, and jejunal epithelial cells from 20 day old Wistar rats. Addition of amphotericin B to the mucosal side stimulated I sc in a concentration dependent manner (Caco-2 cells, EC 50=0.9 [0.5, 1.7] μM; rat jejunum, EC 50=7.4 [0.8; 70.1] μM). The presence of 1 μM dopamine did not change the effect of amphotericin B in Caco-2 cells, but produced a significant (P<0.05) decrease in the maximal effect of amphotericin B in the rat jejunum. Dopamine (1 μM), added to the serosal side, did not change the I sc profile in Caco-2 cells, but produced a significant increase in the rat jejunum. This effect was antagonized by SKF 83566 (1 μM), but not S-sulpiride (1 μM), and was mimicked by SKF 38393 (10 nM), but not by quinerolane (10 nM). Basal Na +, K +-ATPase activity (in nmol Pi mg protein −1 min −1) in Caco-2 cells (49.5±0.2) was similar to that observed in isolated rat jejunal epithelial cells (52.3±3.4). Dopamine (1 μM) significantly (P<0.05) decreased Na +,K +-ATPase activity in rat jejunal epithelial cells, but failed to inhibit Na +,K +-ATPase in Caco-2 cells. This effect of dopamine was antagonized by SKF 83566 (1 μM), but not S-sulpiride (1 μM), and was mimicked by SKF 38393 (10 nM), but not by quinerolane (10 nM). The specific binding of [ 3H]-Sch 23390 to the rat intestinal mucosa was saturable with an apparent dissociation constant (K D) of 2.4 (0.4; 4.5) nM and maximum receptor density of 259.8±32.6 fmol/mg protein. No significant specific binding of [ 3H]-Sch 23390 was observed in membranes from Caco-2 cells. In conclusion, the results obtained show that D 1-like receptor mediated effects of dopamine in the rat jejunum on sodium absorption are absent in Caco-2 cells, most probably because this cell line does not express D 1-like dopamine receptors, which ultimately are responsible for the inhibitory effect of the amine upon intestinal Na +,K +-ATPase.
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