title: 1,4-Dihydropyridine binding sites in moss plasma membranes. Properties of receptors for a calcium channel antagonist.
abstract: An increase in cytoplasmic calcium is an early event in hormone (cytokinin)-induced vegetative bud formation in the moss Physcomitrella patens. Whole cell and calcium transport studies have implicated 1,4-dihydropyridine-sensitive calcium channels in this increase in cellular calcium. To understand the molecular nature of the dihydropyridine-sensitive calcium channel, we have established conditions for the binding of the arylazide 1,4-dihydropyridine, [3H]azidopine, to its receptor in moss plasma membranes. [3H]Azidopine bound specifically in a saturable and reversible manner. The KD for [3H]azidopine binding was 5.2 nM and the Bmax was 35.6 pmol/mg of protein. Association and dissociation of the receptor and [3H]azidopine were temperature-dependent, and association varied as a function of pH. Binding was inhibited by dihydropyridine, phenylalkylamine, and benzothiazepine calcium channel blockers, bepridil, lanthanum, and N-ethylmaleimide. [3H]Azidopine binding was stimulated by cations including calcium, strontium, manganese, and barium. [3H]Azidopine binding was also stimulated by cytokinin with a Km value for kinetin of 0.13 nM. These studies utilize a simple plant system to provide a biochemical framework for understanding calcium regulation during development and have implications for understanding mechanisms of signal transduction in plants.
authors.affiliation: Department of Plant Sciences, University of Arizona, Tucson 85721, USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Schumaker
authors.forename: M J
authors.initials: MJ
authors.lastname: Gizinski
mesh_terms: D001386:Azides / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002413:Cations, Divalent; D002462:Cell Membrane / Q000378:metabolism; D003583:Cytokinins / Q000494:pharmacology; D004095:Dihydropyridines / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D063245:Plant Development; D010944:Plants / Q000187:drug effects / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013696:Temperature
chemical_list: D001386:Azides; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002413:Cations, Divalent; D003583:Cytokinins; D004095:Dihydropyridines; D013439:Sulfhydryl Reagents; C041130:azidopine; C038806:1,4-dihydropyridine; D002118:Calcium