Abstract

In renal proximal tubules, the basolateral organic anion [p-aminohippurate (PAH)] transporter is functionally coupled to the sodium-dependent dicarboxylate transporter. This study was undertaken to elucidate whether protein kinases differentially modulate the activities of these transporters. In isolated S₂ segments of proximal tubules microdissected from rabbit kidneys, we investigated whether the transporters are regulated by tyrosine kinases, phosphatidylinositol 3-kinase (PI3K), and mitogen-activated protein kinase (MAPK). The tubules were collapsed; hence, tubular uptake of the marker substances [³H]PAH and [¹⁴C]glutarate reflects transport across the basolateral cell membrane. Genistein, a selective inhibitor of tyrosine kinase, diminished PAH uptake at 10⁻⁷ M by 15.6 ± 11.7% and at 10⁻⁶ M by 25.6 ± 9.1%. An inactive analog of genistein, diadzein, was without effect even at a concentration 100-fold higher than the lowest concentration of genistein, which produced significant reduction of PAH uptake. At 10⁻⁷ M, wortmannin, a selective inhibitor of PI3K, reduced PAH uptake by 24.1 ± 11.3% and, at 10⁻⁶ M, it reduced it by 32.9 ± 11.8%. The selective inhibitor of MAPK, PD98059, diminished PAH uptake at 5 × 10⁻⁵ M by 23.2 ± 6.8% and at 10⁻⁴ M by 18.3 ± 5.2%. Glutarate uptake was not reduced by any of these protein kinase inhibitors. Insulin had no effect on PAH uptake. These findings indicate that, in addition to protein kinase A, protein kinase C and calcium/calmodulin-dependent protein kinase II (former studies from this laboratory), as well as tyrosine kinases, PI3K, and MAPK, modulate renal basolateral PAH transport, whereas none of these protein kinases affects basolateral glutarate transport. Thus, the results provide evidence for differential regulation of basolateral transporters for PAH and dicarboxylates.