Cuauhtémoc Hidalgo

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Triads isolated from frog and rabbit skeletal muscle were equilibrated with different external [Ca2+], ranging from 0.025 to 10 mM. Vesicular calcium increased with external [Ca2+] as the sum of a linear plus a saturable component; the latter, which vanished after calsequestrin removal, displayed Bmax values of 182 and 132 nmol of calcium/mg of protein,(More)
Endoplasmic reticulum vesicles isolated from rat brain cortex and fused with lipid bilayers displayed ryanodine-sensitive calcium channels, with three cytoplasmic calcium dependences. A: Channels (n=5) stimulated by Ca2+ (K0.5=1.2 microM and nHill=1.9) and not inhibited up to 0.5 mM Ca2+. B: Channels (n=14) cooperatively activated (K0.5=6.9 microM and(More)
The calcium dependence of ryanodine-sensitive single calcium channels was studied after fusing with planar lipid bilayers sarcoendoplasmic reticulum vesicles isolated from excitable tissues. Native channels from mammalian or amphibian skeletal muscle displayed three different calcium dependencies, cardiac (C), mammalian skeletal (MS), and low fractional(More)
Sarcoplasmic reticulum vesicles isolated from fast-twitch frog skeletal muscle presented two classes of binding sites for ryanodine, one of high affinity (Kd1 = 1.7 nM, Bmax1 = 3.3 pmol per mg) and a second class with lower affinity (Kd2 = 90 nM, Bmax2 = 7.0 pmol per milligram). The calcium channels present in the sarcoplasmic reticulum membranes were(More)
We have used spin labels and electron paramagnetic resonance (EPR) to study the correlation between the rotational dynamics of protein and lipid in sarcoplasmic reticulum (SR) membranes. A short-chain maleimide spin label was used to monitor the submillisecond rotational mobility of the Ca-ATPase enzyme (using saturation transfer EPR); a free fatty acid(More)
Analysis of the structure and function of native thick (myosin-containing) filaments of muscle has been hampered in the past by the difficulty of obtaining a pure preparation. We have developed a simple method for purifying native myosin filaments from muscle filament suspensions. The method involves severing thin (actin-containing) filaments into short(More)
Triad vesicles from frog skeletal muscle exhibited calcium-induced calcium release highly sensitive to extravesicular pH; calcium induced release at pH > 7.4 but not at pH 6.8. In contrast, triads isolated from rabbit skeletal muscle exhibited significant calcium-induced calcium release at pH 6.8. At pH 7.4, there was no stimulation of calcium release in(More)
In cardiac sarcolemmal vesicles, MgATP stimulates Na+/Ca2+ exchange with the following characteristics: 1) increases 10-fold the apparent affinity for cytosolic Ca2+; 2) a Michaelis constant for ATP of approximately 500 microM; 3) requires micromolar vanadate while millimolar concentrations are inhibitory; 4) not observed in the presence of 20 microM eosin(More)
The effect of halothane on calcium release kinetics was studied in triad-enriched sarcoplasmic reticulum vesicles from frog skeletal muscle. Release from vesicles passively equilibrated with 3 mM 45CaCl2 was measured in the millisecond time range by use of a fast-filtration system. Halothane (400 microM) increased release rate constants at pH 7.1 and 7.4 as(More)
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