title: Expression of dihydropyridine binding sites in renal epithelial cells.
abstract: It has recently been shown that rabbit kidney epithelial cells (proximal tubule) possess two dihydropyridine (DHP)-sensitive calcium entry channels (1, 2). To evaluate the properties of the DHP binding sites, the binding of the DHP, [3H]PN200-110, was studied in epithelial cell membrane fractions (proximal tubule) of rabbit kidney cortex. High-affinity binding sites for the DHP were observed in both basolateral and apical membranes and in a membrane microsomal preparation from rabbit primary cultures of proximal tubule cells (cultured PT). In an extended analysis of the basolateral membrane preparation, two high-affinity binding sites were evident with binding dissociation constants, Kd, of 0.005 and 0.75 nM. The Kd values are similar to that observed for L-type calcium channel alpha1-subunits. Using a homology-based cloning strategy, a 388-base fragment of an alpha1-subunit was cloned from RNA isolated from rabbit cultured PT cells and freshly isolated proximal tubules and found to encode a protein identical to the cardiac form of the L-type alpha1-subunit (alpha1C-subunit). It is concluded that renal epithelial cells express high-affinity dihydropyridine receptors and that the receptors may be components of plasma membrane calcium channels, including L-type calcium channels, that control calcium entry in these cells.
authors.affiliation: Department of Integrative Biology, Pharmacology, and Physiology, University of Texas-Houston Health Science Center, 77030, USA.
authors.forename: R G
authors.initials: RG
authors.lastname: O'Neil
authors.forename: J M
authors.initials: JM
authors.lastname: Reid
authors.forename: R L
authors.initials: RL
authors.lastname: Williams
authors.forename: N J
authors.initials: NJ
authors.lastname: Karin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015220:Calcium Channels / Q000096:biosynthesis*; D020746:Calcium Channels, L-Type; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004848:Epithelium / Q000378:metabolism; D017275:Isradipine / Q000378:metabolism; D007672:Kidney Cortex / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011817:Rabbits; D011994:Recombinant Proteins / Q000096:biosynthesis; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D017275:Isradipine