title: Active transport of calcium in Neurospora plasma membrane vesicles.
abstract: Functionally inverted plasma membrane vesicles isolated from the eukaryotic microorganism Neurospora crassa catalyze Mg2+/ATP-dependent Ca2+ uptake. Inhibitors induced efflux studies and isotope-exchange experiments indicate that the Ca2+ is accumulated inside the vesicles against a concentration gradient of about 40-fold, and that the majority of the transported Ca2+ is present essentially in free solution. Comparisons of Mg2+/ATP-driven 45Ca2+ uptake and [14C]SCN-uptake with respect to the Mg2+/ATP concentration dependence, the effects of inhibitors, and the nucleotide and divalent cation specificities indicate that the energy for Ca2+ accumulation is derived from ATP hydrolysis catalyzed by the electrogenic plasma membrane ATPase. Energized Ca2+ uptake is stimulated by the permeant anion SCN- to a degree that varies reciprocally with the ability of this anion to dissipate the membrane potential, and is inhibited by K+ in the presence of nigericin. All of these data point to the conclusion that the active transport of Ca2+ across the Neurospora plasma membrane takes place via a Ca2+/H+ antiporter, which functions to pump Ca2+ out of the intact cell.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism; D009491:Neurospora / Q000378:metabolism*; D009492:Neurospora crassa / Q000378:metabolism*; D009550:Nigericin / Q000494:pharmacology; D013861:Thiocyanates / Q000494:pharmacology
chemical_list: D013861:Thiocyanates; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D008274:Magnesium; D009550:Nigericin; D002118:Calcium