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Using highly purified sarcolemmal vesicles isolated from dog ventricles, we examined the effects of pH on Na+-Ca2+ exchange. The initial rate of Nai+-dependent Ca2+ uptake is a sigmoid function of pH. The Ca2+ uptake is inhibited at pH 6 and stimulated at pH 9 (as compared with uptake at pH 7.4). This dependence on pH suggests that the ionization state of a(More)
The sidedness of isolated rabbit cardiac sarcolemmal vesicles was studied by observing the effects of several permeability-increasing agents on measurements of the amount of sialic acid released by neuraminidase, specific ouabain binding, and K+-phosphatase and (Na+ + K+)-ATPase activities. The results suggest that the vesicles are sealed and are about 80%(More)
Although the enzyme (Na+ + K+)-ATPase has been extensively characterized, few studies of its major role, ATP-dependent Na+ pumping, have been reported in vesicular preparations. This is because it is extremely difficult to determine fluxes of isotopic Na+ accurately in most isolated membrane systems. Using highly purified cardiac sarcolemmal vesicles, we(More)
Studies are presented that relate the calcium binding of isolated sarcolemmal membranes to myocardial contractility. The contractile strength of the perfused rabbit interventricular septum as a function of perfusate calcium concentration is compared with calcium bound to isolated rabbit sarcolemma at the same calcium concentrations. If the calcium-binding(More)
The influence of external Na+ and Ca2+ on the efflux of Ca2+ from highly purified sarcolemmal vesicles isolated from dog ventricles is examined. Na+-Ca2+ exchange is used to initially load the vesicles with Ca2+. Ca2+-induced Ca2+ efflux is activated if a monovalent cation is also present in the efflux medium. The order of potency of monovalent cations in(More)
The Na+-Ca2+ exchange activity of purified canine cardiac sarcolemmal vesicles can be strikingly stimulated if the vesicles are pretreated with a serine or thiol proteinase. The Km (Ca2+) for Na+i-dependent Ca2+ influx is reduced from 22.2 +/- 2.3 to 8.1 +/- 0.3 microM while Vmax is increased from 15.1 +/- 3.6 to 18.9 +/- 5.2 nmol Ca2+ . mg protein-1 . s-1.(More)
c-MYC overexpression is frequently observed in various cancers including colon cancer and regulates many biological activities such as aberrant cell proliferation, apoptosis, genomic instability, immortalization and drug resistance. However, the mechanism by which c-MYC confers drug resistance remains to be fully elucidated. In this study, we found that the(More)
Treatment of canine cardiac sarcolemmal vesicles with phospholipase D resulted in a large stimulation (up to 400%) of Na+-Ca2+ exchange activity. The phospholipase D treatment decreased the apparent Km (Ca2+) for the initial rate of Nai+-dependent Ca2+ uptake from 18.2 +/- 2.6 to 6.3 +/- 0.3 microM. The Vmax increased from 18.0 +/- 3.6 to 31.5 +/- 3.6 nmol(More)