AJP - Renal Physiology, Vol 245, Issue 6 701-F706, Copyright © 1983 by American Physiological Society
Pi transport, phosphorylation, and dephosphorylation in renal membranes from HYP/Y mice
M. R. Hammerman and L. R. Chase
To ascertain whether cAMP-dependent phosphorylation could be demonstrated
in brush border membrane vesicles (BBMV) isolated from kidneys of mice with
X-linked hypophosphatemic rickets (HYP/Y) and normal littermates (+/Y) and,
if so, to determine whether the absence of dephosphorylation might underlie
differences in Na+-dependent 32Pi transport in BBMV, we measured 1) 32Pi
transport, 2) cAMP-dependent phosphorylation, and 3) dephosphorylation in
BBMV from +/Y and HYP/Y mice. Na+ gradient-dependent 32Pi transport was
decreased in BBMV from HYP/Y mice as reflected in a decreased apparent
Vmax. cAMP-dependent phosphorylation of a 62,000 Mr protein was
demonstrated in sodium dodecyl sulfate polyacrylamide gels of BBMV from +/Y
and HYP/Y mice and was associated with decreased Na+-dependent 32Pi
transport. Dephosphorylation of the 62,000 Mr band was demonstrable in both
types of membranes. Thus, both cAMP-dependent protein kinase and
phosphoprotein phosphatase activities were demonstrable in BBMV isolated
from +/Y and HYP/Y mice. These results are consistent with the renal
tubular defect in the HYP/Y mouse reflecting an intrinsic abnormality of Pi
transport in the brush border membrane independent from mediation of the
phosphaturic effect of parathyroid hormone.
