Comparative study on sodium transport and Na+,K+-ATPase activity in Caco-2 and rat jejunal epithelial cells: effects of dopamine.
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 Isc in a concentration dependent manner (Caco-2 cells, EC50=0.9 [0.5, 1.7] microM; rat jejunum, EC50=7.4 [0.8; 70.1] microM). The presence of 1 microM 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 microM), added to the serosal side, did not change the Isc profile in Caco-2 cells, but produced a significant increase in the rat jejunum. This effect was antagonized by SKF 83566 (1 microM), but not S-sulpiride (1 microM), 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 microM) 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 microM), but not S-sulpiride (1 microM), 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 (KD) 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 D1-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 D1-like dopamine receptors, which ultimately are responsible for the inhibitory effect of the amine upon intestinal Na+,K+-ATPase.
Vieira-Coelho
M A
MA
Institute of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal.
Soares-da-Silva
P
P
D000666:Amphotericin B / Q000494:pharmacology; D000818:Animals; D001552:Benzazepines / Q000378:metabolism; D018938:Caco-2 Cells; D004298:Dopamine / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D017136:Ion Transport; D007583:Jejunum / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D001552:Benzazepines; D000666:Amphotericin B; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D004298:Dopamine