These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Canine cardiac sarcolemmal vesicles demonstrate rapid initial Na(+)-Ca2+ exchange activity.
    Author: Gruver CL, Katz AM, Messineo FC.
    Journal: Circ Res; 1990 May; 66(5):1171-7. PubMed ID: 2335019.
    Abstract:
    To identify a rapid, uninhibited rate of exchange activity, we investigated in canine sarcolemmal vesicles the rapid kinetics of Na(+)-Ca2+ exchange. Sarcolemmal vesicles were incubated in 160 mM NaCl and 20 mM HEPES at 25 degrees C (pH 7.4) and actively loaded with 45Ca2+ for 2 minutes by Na(+)-Ca2+ exchange. After further uptake was inhibited by dilution into 0.15 mM Na(+)-free EGTA, sarcolemmal vesicles were immobilized on a rapid filtration apparatus that allowed millisecond resolution of 45Ca2+ fluxes. In the presence of external NaCl (Na+o) but not other monovalent cations (i.e., K+, Li+), a biphasic pattern of Ca2+ release was observed--an initial brief and rapid rate of Ca2+ release followed by a second slower, prolonged phase of Ca2+ release. Semilogarithmic plots of sarcolemmal Ca2+ content versus time were not linear but were consistent with a biexponential rate of Na+o-induced Ca2+ release during the first several seconds of the exchange reaction. The fast phase of Na+o-stimulated Ca2+ release was several thousand-fold more rapid than that in the absence of Na+o. Both phases of Ca2+ release showed a similar Na+o dependence (Km, approximately 12 mM) with evidence of a positive cooperative effect of Na+. Vmax of the fast and slow phases were approximately 37.0 and approximately 0.76 nmol/mg/sec, respectively. Using rapid-reaction techniques, we demonstrated in the present study that the initial velocity of sarcolemmal Na(+)-Ca2+ exchange activity is greater than previously reported in sarcolemmal vesicles and that this exchange process exhibits complex rate behavior with a biphasic pre-steady state kinetic pattern.
    [Abstract] [Full Text] [Related] [New Search]