Transport Mechanisms of Carnosine in SKPT Cells: Contribution of Apical and Basolateral Membrane Transporters

Abstract

Purpose-The aim of this study was to investigate the transport properties of carnosine in kidney using SKPT cell cultures as a model of proximal tubular transport, and to isolate the functional activities of renal apical and basolateral transporters in this process. Results-Carnosine uptake was 15-fold greater from the apical than basolateral surface of SKPT cells. However, the apical-to-basolateral transepithelial transport of carnosine was severely ratelimited by its cellular efflux across the basolateral membrane. The high-affinity, protondependence, concentration-dependence and inhibitor specificity of carnosine supports the contention that PEPT2 is responsible for its apical uptake. In contrast, the basolateral transporter is saturable, inhibited by PEPT2 substrates but non-concentrative, thereby, suggesting a facilitative carrier. Methods-TheConclusions-Carnosine is expected to have a substantial cellular accumulation in kidney but minimal tubular reabsorption in blood because of its high influx clearance across apical membranes by PEPT2 and very low efflux clearance across basolateral membranes.

Muscle Carnosine Metabolism and β-Alanine Supplementation in Relation to Exercise and Training

“…Evidence for the regulated carnosine release from muscle into the circulation is fragmentary at present. Carnosine can be transported as an intact dipeptide across the plasma membrane through proton-coupled oligopeptide transporters (PEPT1, PEPT2, PHT) [16][17][18]. Kamal et al [19] have recently shown that the genetic knockout of PEPT2 in mice results in a decreased tissue carnosine content in spleen, kidney and olfactory bulb.…”

Influence of genetic knockout of Pept2 on the in vivo disposition of endogenous and exogenous carnosine in wild-type and Pept2 null mice

“…In comparison, two-to threefold changes were observed between wild-type and knockout mice for the renal clearances of glycylsarcosine and cefadroxil. As demonstrated in SKPT cells, carnosine is expected to have a substantial cellular accumulation in kidney but minimal tubular reabsorption to blood because of its high influx clearance across apical membranes by PEPT2 and very low efflux clearance across basolateral membranes (13). In the absence of PEPT2, the kidney/plasma concentration ratio of carnosine was reduced sixfold.…”

“…Given the very low concentrations of endogenous carnosine in plasma (Ͻ3 M), compared with K m ϭ 50 M for apical carnosine transport in SKPT cells expressing PEPT2 (13) and K m ϭ 60 M for carnosine metabolism by purified mouse kidney carnosinase (17), it is very unlikely that these concentrations would affect the disposition of exogenous carnosine. Our current findings with exogenous carnosine are consistent with previous studies in which the in vivo disposition of glycylsarcosine (20) and cefadroxil (25) was examined in wild-type and Pept2 null mice.…”

Carnosine Catalyzes the Formation of the Oligo/Polymeric Products of Methylglyoxal

“…Cellular uptake of carnosine occurs by proton-coupled oligopeptide transporters (POTs), membrane proteins that translocate various small peptides and peptide-like drugs across the biological membrane via an inwardly-directed proton gradient and negative membrane potential [15]. At present, four members of the POT family, namely PEPT1 (SLC15A1), PEPT2 (SLC15A2), PHT1 (SLC15A4) and PHT2 (SLC15A3), have been identified in mammals [16]. Unlike PEPT1 and PEPT2, PHT1 [17] and PHT2 also transport a single amino acid, L-histidine, in addition to the proton-stimulated transport of di- and tripeptides.…”