Ca2+ uptake to purified secretory vesicles from bovine neurohypophyses.
Purified secretory vesicles isolated from bovine neurohypophyses were found to take up Ca2+ when incubated at 30 degrees C in media containing 10(-7) to 10(-4) M free Ca2+. At 10(-4) free Ca2+ 19 nmol/mg protein were taken up within 30 min. The initial uptake at this Ca2+ concentration was about 2 nmol/mg protein per min. The uptake of Ca2+ to secretory vesicles was not affected by ATP, oligomycin, ruthenium red, trifluoperazine, Mg2+ or K+, but was inhibited by Na+ and Sr2+. From these characteristics it can be concluded that the uptake system does not utilize directly ATP (as the Ca2+-ATPases known to be present in the cell membrane and the endoplasmic reticulum) and is different from the mitochondrial Ca2+ uptake system driven by respiration and/or ATP hydrolysis. However, Ca2+-Na+ exchange may well operate: In experiments using different concentrations of Na+ we found half-maximal inhibition of Ca2+ uptake with 33.3 mM Na+. An analysis of the data in a Hill plot indicated that at least 2 Na+ would be exchanged for 1 Ca2+. Also, it was found that Ca2+ previously taken up could be released again by external Na+ but not by K+.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D003594:Cytoplasmic Granules / Q000378:metabolism*; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D009490:Neurosecretory Systems / Q000378:metabolism; D010121:Oxytocin / Q000032:analysis; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D014667:Vasopressins / Q000032:analysis
D014667:Vasopressins; D010121:Oxytocin; D008094:Lithium; D012964:Sodium; D011188:Potassium; D002118:Calcium