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Ca 2+ Mg 3+ ‐ATPase activity in erythrocyte membranes in hypercalciuric nephrolithiasic patients
Author(s) -
HEGUILÉN Ricardo M,
GIMENEZ Maria I,
IMPERIALI Nora,
BERNASCONI Amelia R,
ALGRANATI S Luis,
FARÍAS Eduardo DOS RAMOS
Publication year - 2002
Publication title -
nephrology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 61
eISSN - 1440-1797
pISSN - 1320-5358
DOI - 10.1046/j.1440-1797.2002.00072.x
Subject(s) - hypercalciuria , calcium , medicine , endocrinology , calmodulin , atpase , enzyme , enzyme assay , calcium pump , membrane , red blood cell , chemistry , biochemistry
SUMMARY: Ca 2+ Mg 2+ ATPase is an enzyme involved in calcium transport across biological membranes. In order to determine its possible role in the pathogenesis of calcium nephrolithiasis, we assessed Ca 2+ Mg 2+ ‐ATPase activity in erythrocyte membranes from 18 hypercalciuric (HC) nephrolithiasic patients (nine with absorptive hypercalciuria (AHC), nine with renal hypercalciuria (RHC)) and eight normocalciuric healthy controls (C). Participants took no medication for at least 3 months before the study and remained on a diet containing approximately 25 mmol of calcium per day for 14 days. Pump activity was measured in calmodulin‐free red blood cell membranes and expressed in umol of phosphate released per mg of membrane protein per h. There were statistically significant differences in pump activity between groups (1.43±0.07; 1.93±0.1; 1.65±0.06; C, AHC, RHC, respectively, P < 0.005 (three groups) and P < 0.02 AHC versus RHC. Enzyme activity was positively correlated with 24‐h urinary calcium excretion (r = 0.64, P < 0.01) in HC patients; no such relationship was found in C. In conclusion, erythrocyte membrane Ca 2+ Mg 2+ ATPase activity is increased in HC. Differences in enzyme activity between AHC and RHC may reflect different degrees of a single generalized epithelial calcium transport disturbance.