Na+-dependent, alpha-adrenergic mobilization of intracellular (mitochondrial) Ca2+ in brown adipocytes.
The existence and significance of a hormone-sensitive, rapidly mobilizable intracellular pool of Ca2+ in hamster brown-fat cells was investigated with 45Ca2+-labelling techniques. It was shown that such a pool existed and was probably located within the abundant mitochondria. It was rapidly mobilized by norepinephrine (median effective concentration 50 nM) through alpha-adrenergic mechanisms. The mobilization of Ca2+ from the intracellular stores (mitochondria) required the presence of extracellular Na+, but not of Ca2+, K+ or Mg2+. It is concluded that the experiments are in agreement with a hypothesis linking the mobilization of intracellular Ca2+ pools with an alpha-adrenergically-induced increase in plasma membrane Na+ permeability (observed as a membrane depolarization), and a subsequent activation of the mitochondrial Na+/Ca2+ exchange, leading to mobilization of mitochondrial Ca2+ and the mediation of alpha-adrenergic effects as a result of an elevated cytosolic Ca2+ level.
D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008647:Mesocricetus; D008928:Mitochondria / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012964:Sodium / Q000378:metabolism / Q000502:physiology*
D011942:Receptors, Adrenergic, alpha; D012964:Sodium; D002118:Calcium; D009638:Norepinephrine