title: cGMP (guanosine 3',5'-cyclic monophosphate) transport across human erythrocyte membranes.
abstract: Human erythrocytes produce cGMP that can be eliminated by phosphodiesterases or active efflux transporters. The efflux can be studied under controlled conditions as ATP-dependent uptake into inside-out membrane vesicles. However, widely differing values for the transport rates have been reported. We have here examined factors that influence the uptake rates measured and thus may explain these discrepancies. Both the ionic composition of the buffer used during uptake and the mode of vesicle preparation were found to affect the observed transport rates. Furthermore it was apparent that different blood donors expressed on their erythrocytes different amounts of both MRP4 and MRP5, transporters that have been putatively linked to cGMP efflux across erythrocyte membranes. These differences in expression were reflected in differences in rates of cGMP uptake into inside-out erythrocyte membrane vesicles. Calculations based on the transport rates observed using vesicles suggest that efflux may be the principal means for eliminating cGMP from human erythrocytes.
authors.affiliation: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB21PD, UK.
authors.forename: Chung-Pu
authors.initials: CP
authors.lastname: Wu
authors.forename: Hannah
authors.initials: H
authors.lastname: Woodcock
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Hladky
authors.forename: Margery A
authors.initials: MA
authors.lastname: Barrand
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001693:Biological Transport, Active; D015153:Blotting, Western; D002021:Buffers; D006152:Cyclic GMP / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism; D014316:Tritium
chemical_list: D000255:Adenosine Triphosphate; D002021:Buffers; D006152:Cyclic GMP; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D014316:Tritium; C073492:ABCC4 protein, human; C120809:ABCC5 protein, human