Ontogeny up-regulates renal Na +/Cl −/creatine transporter in rat

Abstract

Creatine plays a role in energy storage and transport/shuttle of high-energy phosphate in heart, brain, retina, testis and skeletal muscle. These tissues take creatine from the plasma via a 2Na +/1Cl −/1creatine cotransporter (CRT). We have previously demonstrated that renal apical membrane presents a 2Na +/1Cl −/1creatine cotransport activity. The goal of this study was to determine whether this transporter is ontogenically regulated. Na +/Cl −/creatine transport activity was evaluated by measuring [ 14C]-creatine uptake into renal brush-border membrane vesicles. CRT mRNA expression was measured by Northern and real-time PCR assays. E20 foetuses, newborn, suckling, weaning and adult (2- and 8-month-old) Wistar rats were used. The results revealed that neither the vesicular volume, the binding of creatine to the brush-border membrane vesicles, nor the purity of the brush-border membrane vesicle preparations was affected by maturation. Fetal and neonatal kidneys contained a creatine transporter that was qualitatively indistinguishable from that in the adult: it was concentrative, Na +- and Cl −-dependent, electrogenic and inhibited by guanidinopropionic acid. Maturation increased this transport activity by increasing the maximal rate of transport ( V max) without significantly changing the apparent K m. Northern analysis revealed two transcripts for CRT of 2.7 kb and 4.2 kb in all the ages tested. Northern and real-time PCR assays showed that, as seen with NaCl-dependent creatine transport activity, maturation increased CRT mRNA expression. This study reports for the first time that: (i) an apical renal Na +/Cl −/creatine cotransporter is already active in rat foetuses and (ii) development regulates Na +/Cl −/creatine cotransport activity by increasing the density and/or turnover of the transporters.