ABSTRACT
Rabbit kidney proximal convoluted tubule (RPCT) and proximal straight tubule (RPST) cells were independently isolated and cultured. The kinetics of the sodium-dependent glucose transport was characterized by determining the uptake of the glucose analog alpha-methylglucopyranoside. Cell culture and assay conditions used in these experiments were based on previous experiments conducted on the renal cell line derived from the whole kidney of the Yorkshire pig (LLC-PK1). Results indicated the presence of two distinct sodium-dependent glucose transporters in rabbit renal cells: a relatively high-capacity, low-affinity transporter (V(max) = 2.28 +/- 0.099 nmoles/mg protein min, Km = 4.1 +/- 0.27 mM) in RPCT cells and a low-capacity, high-affinity transporter (V(max) = 0.45 +/- 0.076 nmoles/mg protein min, K(m) = 1.7 +/- 0.43 mM) in RPST cells. A relatively high-capacity, low-affinity transporter (V(max) = 1.68 +/- 0.215 nmoles/mg protein min, Km = 4.9 +/- 0.23 mM) was characterized in LLC-PK1 cells. Phlorizin inhibited the uptake of alpha-methylglucopyranoside in proximal convoluted, proximal straight, and LLC-PK1 cells by 90, 50, and 90%, respectively. Sodium-dependent glucose transport in all three cell types was specific for hexoses. These data are consistent with the kinetic heterogeneity of sodium-dependent glucose transport in the S1-S2 and S3 segments of the mammalian renal proximal tubule. The RPCT-RPST cultured cell model is novel, and this is the first report of sodium-dependent glucose transport characterization in primary cultures of proximal straight tubule cells. Our results support the use of cultured monolayers of RPCT and RPST cells as a model system to evaluate segment-specific differences in these renal cell types.
