Kinetics of ATP-dependent Ca2+ uptake by permeabilized rat enterocytes. Effects of inositol 1,4,5-trisphosphate.
Isolated rat enterocytes were permeabilized by saponin treatment. 45Ca2+ was accumulated by these cells when provided with ATP in a medium containing Ca2+ ligands. The use of oxalate, vanadate and mitochondrial inhibitors indicated that both non-mitochondrial and mitochondrial pools are involved. Kinetic analysis of non-mitochondrial Ca2+ uptake revealed a Km of 0.1 microM Ca2+ and a Vmax of 0.4 nmol Ca2+/mg protein X min for this Ca2+-pumping ATPase activity. Mitochondria started to take up Ca2+ between 0.2 and 0.3 microM free Ca2+ reaching maximal rates around 2 microM. At 1 microM free Ca2+ mitochondria accumulated 20 times more Ca2+ than the non-mitochondrial pool. Inositol 1,4,5-trisphosphate released 40% of the Ca2+ content of the non-mitochondrial pool. Half-maximal release was observed at 0.5 and 1.5 microM IP3 in duodenal and ileal cells respectively. These findings support the possibility that the phosphatidyl inositide metabolism plays a role in regulation of electrolyte transport in enterocytes.
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D007408:Intestinal Absorption / Q000187:drug effects*; D007421:Intestine, Small / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D012503:Saponins / Q000494:pharmacology; D013403:Sugar Phosphates / Q000494:pharmacology*; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology
D007295:Inositol Phosphates; D012503:Saponins; D013403:Sugar Phosphates; D014639:Vanadium; D014638:Vanadates; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D002118:Calcium