Calmodulin-mediated effects of loperamide on chloride transport by brush border membrane vesicles from human ileum.
We investigated whether the synthetic opiate loperamide-HCl is able to regulate specific transport systems for sodium and chloride in brush border membrane vesicles (BBMVs) from human ileum and whether such activities are mediated by calcium/calmodulin. In BBMVs we studied Na+/H+ antiport, Cl+/OH- antiport, Na+/Cl- cotransport, and the Cl- conductive pathway. Brush border membrane vesicles were incubated with 10 microM loperamide over 4 h at 5 degrees C before the uptake experiments. In ileal BBMVs, loperamide stimulated intravesicular accumulation of Na+ in the presence of Cl- and vice versa. After 1 min of incubation, the stimulatory effect was 35% +/- 5% (p less than 0.005) of the control without loperamide. Loperamide also stimulated Cl-/OH- antiport by 30% +/- 5% (p less than 0.005) in BBMVs of ileum. In addition, we studied the role of Ca2+/calmodulin in the action of loperamide on chloride transport by human BBMVs. In loperamide-pretreated BBMVs, calmodulin activity was significantly decreased (12 +/- 2 vs. 38 +/- 4 pmol/mg protein). When loperamide-pretreated vesicles were incubated with 2 microM calcium (free concentration) plus 5 microM calmodulin for 1 h at 5 degrees C, complete inhibition of the stimulatory effect of loperamide on Cl-/OH- antiport and Na+/Cl- cotransport was observed. Increasing the Ca2+/calmodulin activity of loperamide-pretreated BBMVs with 2 microM calcium plus 5 microM calmodulin led to a significant inhibition of Cl-/OH- antiport and Na+/Cl- cotransport by 40% +/- 5% (p less than 0.005).
Stoll
R
R
Department of Medicine, University of Erlangen-Nuremberg, Federal Republic of Germany.
Ruppin
H
H
Domschke
W
W
D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000502:physiology; D002147:Calmodulin / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism*; D006801:Humans; D007082:Ileum / Q000378:metabolism* / Q000648:ultrastructure; D066298:In Vitro Techniques; D008139:Loperamide / Q000494:pharmacology*; D008871:Microvilli / Q000378:metabolism; D010880:Piperidines / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D049992:Sodium Chloride Symporters; D017923:Sodium-Hydrogen Exchangers; D027981:Symporters
D002147:Calmodulin; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D010880:Piperidines; D049992:Sodium Chloride Symporters; D017923:Sodium-Hydrogen Exchangers; D027981:Symporters; D008139:Loperamide; D012964:Sodium; D002118:Calcium