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, [H]azidopine, to its receptor in moss plasma membranes. [H]Azidopine bound specifically in a saturable and reversible manner. The K for [H]azidopine binding was 5.2 nM and the B was 35.6 pmol/mg of protein. Association and dissociation of the receptor and [H]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. [H]Azidopine binding was stimulated by cations including calcium, strontium, manganese, and barium. [H]Azidopine binding was also stimulated by cytokinin with a Kvalue 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.

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				K. S. Schumaker and M. J. Gizinski G Proteins Regulate Dihydropyridine Binding to Moss Plasma Membranes J. Biol. Chem., August 30, 1996; 271(35): 21292 - 21296. [Abstract] [Full Text] [PDF]