title: Calcium channels.
abstract: A key step in renal calcium reabsorption is dihydropyridine-sensitive calcium entry across the apical membrane of the distal tubule. Electrophysiologic studies have confirmed the existence of calcium channels that may mediate this pathway. Molecular studies of voltage-dependent calcium channels have revealed a surprising degree of heterogeneity. The pore-forming alpha 1 subunit is encoded by multiple genes, each directing the synthesis of several alternatively spliced transcripts whose products may in turn be posttranslationally cleaved to yield multiple differently-sized peptides. Further heterogeneity is afforded by the presence of accessory subunits, such as the beta subunit, which is also encoded by a multigene family. Site-directed mutagenesis studies of the alpha 1 subunit have begun to explore the molecular structure of the calcium pore. Molecular cloning of rat renal calcium channel transcripts has identified alpha 1 and beta subunit genes that are expressed in the distal tubule. Future studies will address the structure-function relationship of various physiologic properties associated with the channels expressed by these genes.
authors: Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115.
authors: A S
authors: AS
authors: Yu
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry / Q000145:classification / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D008956:Models, Chemical; D015394:Molecular Structure
chemical_list: D015220:Calcium Channels; D002118:Calcium