Abnormal effect of thiol groups on erythrocyte Na/Li countertransport kinetics in adult polycystic kidney disease.
BACKGROUND
Evidence suggests that in adult polycystic kidney disease (APCKD) there is abnormal membrane organisation that involves cytoskeletal proteins and affects ion-transport proteins. The possibility of detecting a membrane organisation defect in erythrocytes from APCKD patients was investigated.


METHODS
Na/Li countertransport (CT) kinetics were measured in erythrocytes from APCKD patients compared with normal controls. The modulation of Na/Li CT kinetics by key membrane thiol groups and by dissociation of spectrin by heating was studied.


RESULTS
In erythrocytes from APCKD compared to normal subjects the Km of Na/Li CT was lower (64 SEM 3v 90 SEM 3 mmol Na/l, P < 0.001) and Vmax/Km was higher (6.8 SEM 0.6v 5.3 SEM 0.4 (x 19(-3)), P < 0.05). In erythrocytes from normal subjects, after N-ethylmaleimide (NEM) treatment in choline medium, Km of Na/Li CT was reduced and Vmax/Km increased (59 SEM 5, 8.2 SEM 0.4 (x 10(-3)), P < 0.001) but there was no effect on these kinetic parameters in erythrocytes from APCKD. The effect of heating was similar to that of NEM in choline medium. In normal controls after NEM treatment in sodium medium both Km and Vmax were reduced whereas in APCKD Vmax was reduced but Km was unchanged.


CONCLUSIONS
In APCKD the effect of a key membrane thiol group on Na association with Na/Li CT was absent and the effect of spectrin dissociation was similarily abnormal. A second thiol group effect on the Vmax of Na/Li CT was normal. The results are consistent with a thiol-protein linked to the spectrin cytoskeleton that modulates Na/Li CT and is abnormal in APCKD.
Vareesangthip
K
K
Department of Medicine (Nephrology), University of Newcastle-upon-Tyne, UK.
Thomas
T H
TH
Wilkinson
R
R
D000293:Adolescent; D000328:Adult; D000368:Aged; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D005033:Ethylmaleimide / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008094:Lithium / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D007690:Polycystic Kidney Diseases / Q000188:drug therapy / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000009:adverse effects*
D013439:Sulfhydryl Reagents; D008094:Lithium; D012964:Sodium; D005033:Ethylmaleimide