Alfredo Margreth

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We have investigated high-affinity ryanodine-binding sites in membrane preparations from representative fast-twitch and slow-twitch muscles of the rabbit and rat, as well as from human mixed muscle. Our results, obtained in high-ionic strength binding buffer, demonstrate extensive similarities in binding affinity for [3H]ryanodine (Kd: about 10 nM) and a(More)
Systematic immunological and biochemical studies indicate that the level of expression of sarcoplasmic reticulum (SR) Ca(2+)-ATPase regulatory protein phospholamban (PLB) in mammalian slow-twitch fibers varies from zero, in the rat, to significant levels in the rabbit, and even higher in humans. The lack of PLB expression in the rat, at the mRNA level, is(More)
Regulatory phosphorylation of phospholamban and of SR Ca(2+)-ATPase SERCA2a isoform by endogenous CaM-K II in slow-twitch skeletal and cardiac sarcoplasmic reticulum (SR) is well documented, but much less is known of the exact functional role of CaM K II in fast-twitch muscle SR. Recently, it was shown that RNA splicing of brain-specific alpha CaM K II,(More)
The cardiac and fast-twitch skeletal muscle forms of the Ca2+ -binding protein calsequestrin (CS) are the products of two different genes, both of which are transcribed in slow-twitch skeletal muscle, though at much different rates (Scottet al., 1988., Fliegelet al., 1989). We have investigated this problem more closely at the protein level, on isolated(More)
Skeletal-muscle sarcoplasmic reticulum (SR) comprises two distinct domains, corresponding to the free membrane of longitudinal SR (LSR) and the junctional membrane region of the terminal cisternae (TC), respectively. The junctional membrane contains the ryanodine receptor (RyR)/Ca(2+)-release channel and additional minor protein components that still(More)
An indirect argument in favour of the mechanical hypothesis of excitation-contraction (EC) coupling [Schneider & Chandler (1973) Nature 242, 244-246] is the fixed stoichiometry between the voltage-driven dihydropyridine receptor (DHP-R) on the transverse tubule (TT) and the ryanodine-sensitive Ca2+ channel (RyR) of sarcoplasmic reticulum (SR) terminal(More)
The total number of high-affinity ryanodine receptor (RyR) binding sites present in skeletal and cardiac muscle and in brain tissue of the rabbit was determined by [3H]ryanodine binding to subfractions obtained by differential centrifugation of homogenates prepared in a low-ionic strength medium, containing 0.5% Chaps. In all three tissues at least 80% of(More)
Antibody was raised in chickens against purified sarcoplasmic-reticulum Ca2+-activated ATPase (Ca2+-ATPase). The immunological relationship between the Ca2+-ATPase of fast-muscle and slow-muscle sarcoplasmic reticulum was investigated by a one-step and a two-step competitive enzyme-linked immunosorbent assay (ELISA). The results show marked antigenic(More)
The subcellular distribution of the calmodulin-stimulated plasma-membrane Ca(2+)-ATPase (PMCA) has been studied in rat and rabbit skeletal muscle cells by indirect (calmodulin gel overlays) and direct (Western blotting with specific antibodies) methods. It has also been studied in situ in immunocytochemistry experiments. The distribution of PMCA has been(More)
A calsequentrin (CS)-like glycoprotein is present in the sarcoplasmic reticulum (SR) of chicken pectoralis muscle, which displays unusual properties: it binds relatively low amounts of Ca2+, compared to CS in mammalian skeletal muscle (Yap & MacLennan, 1976), it does not exhibit a marked pH-dependent shift in mobility in sodium dodecyl sulphate(More)