Transport of papaverine in rat kidney cortical slices

Previous results (J. Pharm. Dyn., 7, 342, 1984) from this laboratory indicated that papaverine, a classical phosphodiesterase inhibitor, inhibited the transport of organic anions such as p-aminohippurate (PAH) and urate in rat kidney cortical slices. The transport of papaverine itself, an organic cationic drug, in the kidney is not yet understood. The purpose of this study was to examine the interaction of papaverine with incubated slices and basolateral membrane vesicles prepared from rat kidney cortex, in terms of the possibility of the intracellular action of papaverine in kidney cells. Papaverine was taken up against a concentration gradient by kidney cortical slices and by liver slices. The uptake of papaverine by the former slices was depressed by hypothermia and anoxia with metabolic inhibitors, but that of the drug by the latter slices was not affected by hypothermic condition. Tetraethylammonium (TEA) as a prototype for organic cationic drugs did not depress papaverine transport. TEA also had no effect on the inhibitory effect of papaverine on PAH accumulation in kidney cortical slices. Papaverine, however, inhibited TEA accumulation prominently. Kinetic studies using the slices indicated that papaverine increased the Km for TEA accumulation and decreased Vmax. Then, papaverine inhibition was a "mixed type". TEA uptake by basolateral membrane vesicles was markedly inhibited by papaverine, but PAH uptake by the vesicles was not affected by the drug. The present results indicate that papaverine may be at least partly transported by the same system which handles TEA, but some aspect of the transport system for papaverine may be qualitatively different from that for TEA. Additional studies are required, however, to unequivocally establish the relationships between papaverine and TEA renal transport mechanisms.