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The Madin-Darby canine kidney (MDCK) cell line, derived from distal tubule/ collecting duct, expresses differentiated properties of renal tubule epithelium in culture. We studied the expression of adrenergic receptors in MDCK to examine the role of catecholamines in the regulation of renal function. Radioligand-binding studies demonstrated, on the basis of receptor affinities of subtype-selective adrenergic agonists and antagonists, that MDCK cells have both at-and ~2-adrenergic receptors. To determine whether these receptor types were expressed by the same cell, we developed a number of clonal MDCK cell lines. The clonal lines had stable but unique morphologies reflecting heterogeneity in the parent cell line. Some clones expressed only/~2-adrenergic receptors and were nonmotile, whereas others expressed both ~t-and /~2-receptors and demonstrated motility on the culture substrate at low cell densities. In one clone, a-and/~-receptor expression was stable for more than 50 passages. Catecholamine agonists increased phosphatidylinositol turnover by activating a-adrenergic receptors and cellular cyclic adenosine monophosphate accumulation by activating/3-adrenergic receptors. Guanine nucleotide decreased the affinity of isoproterenol for the ~2-receptor but did not alter the affinity of epinephrine for the c~l-receptor. These results show that c~l-and/32-receptors can be expressed by a single renal tubular cell and that the two receptors behave as distinct entities in terms of cellular response and receptor regulation. Heterogeneity of adrenergic receptor expression in MDCK clones may reflect properties of different types of renal tubule cells.Catecholamines regulate a variety of cellular functions in the mammalian kidney, including tubule water and ion reabsorption, renin release, renal hemodynamics, and gluconeogenesis (20,35). The influence of renal sympathetic nerves (which release catecholamines as neurotransmitters) on renal function has been discussed in several reviews (1,6,32). Catecholamines act on target cells by initially binding to cell surface receptors, and we and others (20,(41)(42)(43) have identified a~-, ~2-, B~-, and/~2-adrenergic receptors in membrane preparations of the kidney cortex by radioligand-binding techniques. However, the sites of action of adrenergic agents along the nephron have not been clearly defined. Determination of the location of catecholamine action within the kidney is particularly important to distinguish indirect adrenergic effects (resulting from changes in vascular tone) from direct effects on epithelial transport and metabolism. The kidney consists of segments that are anatomically and functionally distinguishable, yet each segment may contain several morphologically distinct cell types (8). To understand the regulation of renal function by catecholamines and sympathetic nerves, it therefore is important to study homogeneous populations of renal cells. Such populations may be found in the established renal cell lines, which have provided valuable information r...

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