D. Markovich et al., REGULATION OF OPOSSUM KIDNEY (OK) CELL NA P-I COTRANSPORT BY P-I DEPRIVATION INVOLVES MESSENGER-RNA STABILITY/, Pflugers Archiv, 430(4), 1995, pp. 459-463
Renal proximal tubular Na-dependent phosphate transport (Na/P-i cotran
sport) has been studied extensively in the opossum kidney (OK) cell li
ne. Recently, we cloned a complementary deoxyribonucleic acid (cDNA) (
NaPi-4) from OK cells encoding an apical NaPi cotransport system. OK c
ells exposed to a low-P-i medium, as compared to high-P-i media, respo
nded with an increase in Na/P-i cotransport, which was followed by an
increase in NaPi-4 messenger ribonucleic acid (mRNA) abundance; maxima
l stimulation of Na/P-i cotransport was reached in 2 h, with no furthe
r increase for up to 16 h. NAP(i)-4 mRNA abundance was unaltered for 2
h, then increased to a maximum after 6-16 h in cells treated with low
Pi medium. NaPi-4 mRNA decay rate was lowered by low-P-i media when c
ompared to high-Pi media, with no increase in the NaPi-4 mRNA transcri
ption rate. These data suggest that the upregulation of Na/P-i cotrans
port in OK cells by low-Pi media involves two regulatory mechanisms: a
n immediate (early) increase (after 2 h) in the expression of Na/P-i c
otransport, independent of mRNA synthesis or stability, and a delayed
(late) effect (after 4-6 h), resulting in an increase in NaPi-4 mRNA a
bundance, due to an increased stability.