Characterization and localization of two forms of active Ca2+ transport in vesicles derived from rat submandibular glands.
Energy-dependent Ca2+ uptake was characterized in vesicles derived from rat submandibular salivary glands. Ca2+ transport was stimulated by submicromolar levels of Ca2+, reached a plateau at 1-20 microM Ca2+ then again increased as the Ca2+ concentration rose to millimolar levels. Ruthenium red (2.5 microM) was used to resolve this pattern of uptake into two components: ruthenium red-insensitive Ca2+ transport occurs in the presence of the dye, is stimulated by submicromolar Ca2+ concentrations and reaches a maximum steady state at about 1 microM Ca2+. The distribution of ruthenium red-insensitive Ca2+ uptake in membrane subfractions obtained by differential centrifugation is positively (r = 0.717) and significantly (p = 0.001) correlated with the distribution of membrane-bound RNA in the same subfractions. Ca2+ uptake which is abolished by ruthenium red is greatest at millimolar Ca2+ concentrations. Its distribution is positively (r = 0.828) and significantly (p = 0.0001) correlated with the cytochrome-c oxidase activity of the membrane subfractions but is unrelated to the distribution of particulate RNA and is negatively correlated with Na+-K+ ATPase activity. We conclude that vesicles derived from the endoplasmic reticulum of rat submandibular glands actively transport Ca2+ by a ruthenium red-insensitive mechanism which is stimulated at Ca2+ concentrations typical of the cytosol. Membranes derived from mitochondria also sequester Ca2+ but by a mechanism which is inhibited by ruthenium red and which reaches its maximum steady state capacity at relatively high Ca2+ concentrations.
T W
TW
Hurley
J R
JR
Martinez
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002498:Centrifugation; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000502:physiology; D008297:Male; D012313:RNA / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012430:Ruthenium Red / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013363:Submandibular Gland / Q000378:metabolism*
D012430:Ruthenium Red; D000001:Calcimycin; D012313:RNA; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D002118:Calcium