Modulation of the basolateral and apical step of transepithelial organic anion secretion in proximal tubular opossum kidney cells - Acute effects of epidermal growth factor and mitogen-activated protein kinase

The organic anion transport system in the proximal tubule of the kidney is of major importance for the excretion of a variety of endogenous and potent ially toxic exogenous substances. Furthermore, the clearance of model subst rates (e.g. para-aminohippurate) of this system is used for the determinati on of renal blood flow. We investigated regulation of organic anion secreti on in a way that allowed us to examine simultaneously regulation of overall transepithelial secretion and to estimate the separate contributions of re gulation of the basolateral and apical transport steps to this overall regu lation. The data were verified by measurement of initial basolateral. uptak e rate and initial apical afflux rate. Opossum kidney cells were used as a suitable model system for proximal tubule cells, and [C-14]para-aminohippur ate was utilized as an organic anion. Stimulation of protein kinase C inhib ited transepithelial secretion because of inhibition of both apical efflux and basolateral uptake. Inhibition of the mitogen-activated protein kinase (MAPK) kinase MEK reduced transepithelial secretion via inhibition of basol ateral uptake and apical efflux. Epidermal growth factor (EGF) enhanced tra nsepithelial secretion via stimulation of basolateral uptake but did not af fect apical efflux. EGF induced stimulation of basolateral uptake was aboli shed by inhibition of MEK. EGF led to phosphorylation of ERK1/2, which was also abolished by inhibition of MEK. Thus, EGF stimulated basolateral uptak e of organic anions via MAPKs, Transepithelial organic anion secretion can be regulated at two sites, at least: basolateral uptake and apical efflux. Both steps are under control of protein kinase C and MAPK, The pathophysiol ogically relevant growth factor EGF enhances transepithelial secretion via stimulation of basolateral uptake, EGF stimulates basolateral uptake via ME K and ERK1/2. Thus, renal organic anion extraction may be modulated, especi ally under pathophysiological conditions.