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Effect of activation of protein kinase A and of protein kinase C on the kinetics of the renal basolateral PAH transporter
Author(s) -
Stärk U,
Bergh H Vanden,
Rover N,
Greven J
Publication year - 1998
Publication title -
fundamental and clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.655
H-Index - 73
eISSN - 1472-8206
pISSN - 0767-3981
DOI - 10.1111/j.1472-8206.1998.tb00922.x
Subject(s) - protein kinase c , forskolin , activator (genetics) , chemistry , protein kinase a , medicine , adenosine , endocrinology , cyclic adenosine monophosphate , phorbol , transporter , epithelial polarity , enzyme , biochemistry , biology , membrane , in vitro , receptor , gene
Summary— The aim of the present study was to examine the effect of activation of the protein kinase A (PKA) and protein kinase C (PKC) pathways on 3 H‐p‐aminohippurate (PAH) uptake of isolated S 2 segments of proximal tubules, microdissected from rabbit kidneys without the use of enzymatic agents. Because the tubules were not perfused, and hence were collapsed, the tubular uptake of 3 H‐PAH reflects transport across the basolateral membrane. The phorbol ester phorbol 12‐myristate 13‐acetate (PMA) (10 7 M), an activator of PKC, significantly increased tubular 3 H‐PAH uptake with steady state conditions (by 115%), whereas dibutyryl cyclic adenosine monophosphate (db‐cAMP) (10 ‐4 M) and forskolin (10 ‐4 M) significantly inhibited it (by 42% and 52%, respectively). Kinetic data, which were based on 15 sec PAH uptake measurements, revealed that PMA, after a 10 min incubation period, significantly enhanced Km and Vmax of the PAH transporter (Km from 174 ± 22 to 447 ± 91 μM, Vmax from 2.76 ± 0.24 to 16.67 ± 1.85 pmol nL ‐1 min ‐1 ), whereas db‐cAMP significantly decreased Vmax (from 2.76 ± 0.24 to 1.82 ± 0.19 pmol nL ‐1 min ‐1 ). The Km value was also numerically lowered by dibutyryl‐cAMP (from 174 ± 22 to 139 ± 21 μM), but this change did not reach statistical significance. The data provide evidence that short time activation of the PKC pathway 1) enhances the effectiveness of PAH transport into proximal S 2 segments across the basolateral cell membrane, 2) increases the maximum transport rate of the PAH transporter and 3) decreases its affinity for PAH. Activation of the cAMP/PKA pathway induces the opposite effects.