Release of cAMP from a renal epithelial cell line

LLC-PK1 is an established porcine renal cell line with epithelial characteristics. Upon hormonal stimulation by vasopressin, LLC-PK1 cells release adenosine 3',5'-cyclic monophosphate (cAMP) into the medium. Release of cAMP is inhibited by the organic anion transport inhibitor probenecid and by cold phosphodiesterase inhibitors and iodoacetate but not by prostaglandins A1 or E1. The kinetics of release are first order, and cAMP analogues do not induce the release of cAMP. When grown on cellulose filters, monolayers of LLC-PK1 have morphological characteristics of transporting epithelia (apical microvilli and intercellular tight junctions) and maintain a transepithelial potential difference. Stimulation of such monolayers by vasopressin elicits probenecid-sensitive release of cAMP into the medium bathing the apical surface. Smaller quantities of cAMP are released from the basolateral surface, but release in this direction is not inhibited by probenecid. In contrast, release of cAMP from the nonepithelial cell line BHK is symmetrical and is symmetrically inhibited by probenecid. Probenecid-sensitive release of cAMP from LLC-PK1 is thus a function of the apical (brush-border) membrane.