Release of cyclic nucleotides from the apical and basolateral poles of cultured human glomerular epithelial cells.

We have examined the intracellular accumulation and the release of cGMP and cAMP from the apical and basolateral poles of SV40-transformed human glomerular visceral epithelial cells (HGVEC) cultured on filters. After treatment of the cells by atrial natriuretic peptide (ANP), cGMP did not accumulate in the cells and was rapidly released mainly into the apical medium (86% of its total secretion). Its apical secretion was inhibited by 83% in the presence of probenecid, an organic acid transport inhibitor, and by 90% in the presence of nocodazole, a microtubule disrupter. cAMP was released more slowly than cGMP after it had accumulated in the cells. Apical polarization of the secretion still existed but was less marked than for cGMP (70% of its total secretion). Similarly, probenecid and nocodazole inhibited to a lesser degree cAMP egression (66 and 33%, respectively, for the apical secretion). Polarization of HGVEC was confirmed by the vectorialized secretion of lactate dehydrogenase. These results indicate that cGMP release from HGVEC is essentially apical and depends on a probenecid-sensitive organic acid transport and also on an intact microtubular network. cAMP release appears to be less polarized and less sensitive to the two drugs studied. Vectorially secreted cGMP in the urinary space in response to ANP could act downstream in the nephron and thus permit ANP to stimulate cells which do not necessarily possess ANP receptors.