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Isaac N Pessah

Publications and source records attributed to Isaac N Pessah.

40 records · Page 3Linked to original sources
PubMed2002

Redox sensing properties of the ryanodine receptor complex.

The release mechanism regulating SR Ca2+ homeostasis is significantly more sensitive than the uptake mechanisms. The exquisite sensitivity exhibited by ryanodine-sensitive Ca2+ channel complexes (i.e., ryanodine receptors, RyRs) to functional perturbation by chemically diverse sulfhydryl-modifying compounds can include phases of activation and inhibition that are dependent on the concentration of the reagent used, the length of exposure, and the nature of the chemical reaction the reagent undertakes with sulfhydryl groups. However the exquisite sensitivity of RyR function to sulfhydryl modification has been generally viewed as significant only in pathophysiological processes. The present paper addresses possible physiological importance of the redox sensing properties of the ryanodine receptor complexes (RyRs) and proposes an underlying mechanism. New data is presented that directly measure the pKa of hyperreactive thiols that occur when the closed conformation of the RyR channel complex is assumed, and that appear to be an integral component of the redox sensor.

Animals↗
PubMed2002

Ca2+ activation of RyR1 is not necessary for the initiation of skeletal-type excitation-contraction coupling.

Although an elevation in myoplasmic Ca2+ can activate the skeletal muscle ryanodine receptor (RyR1), the function of this Ca2+ activation is unclear because extracellular Ca2+ influx is unnecessary for skeletal-type EC coupling. To determine whether Ca2+ activation of RyR1 is necessary for the initiation of skeletal-type EC coupling, we examined the behavior of RyR1 with glutamate 4032 mutated to alanine (E4032A-RyR1) because this mutation had been shown to dramatically reduce activation by Ca2+. Proc. Natl. Acad. Sci. USA. 98:2865-2870). Analysis after reconstitution into planar lipid bilayers revealed that E4032A-RyR1 was negligibly activated by 100 microM Ca2+ (P(o) too low to be measured). Even in the presence of both 2 mM caffeine and 2 mM ATP, P(o) remained low for E4032A-RyR1 (ranging from <0.0001 in 100 microM free Ca2+ to 0.005 in 2 mM free Ca2+). Thus, the E4032A mutation caused a nearly complete suppression of activation of RyR1 by Ca2+. Depolarization of E4032A-RyR1-expressing myotubes elicited L-type Ca2+ currents of approximately normal size and myoplasmic Ca2+ transients that were skeletal-type, but about fivefold smaller than those for wild-type RyR1. The reduced amplitude of the Ca2+ transient is consistent either with the possibility that Ca2+ activation amplifies Ca2+ release during EC coupling, or that the E4032A mutation generally inhibits activation of RyR1. In either case, Ca2+ activation of RyR1 does not appear to be necessary for the initiation of Ca2+ release during EC coupling in skeletal muscle.

Adenosine Triphosphate↗
PubMed2002

(+)-7S-Hydroxyxestospongin A from the marine sponge Xestospongia sp. and absolute configuration of (+)-xestospongin D.

The structure of the title compound, (+)-7S-hydroxyxestospongin A was solved by single-crystal X-ray diffraction analysis and the absolute stereochemistry obtained by analysis of the derived R and S Mosher's esters. The absolute configuration of xestospongin D was determined for the first time by analysis of anomalous scattering from the X-ray crystal diffraction data set. Xestospongins A, C, and D, araguspongine C, and demethylxestospongin B exhibited modest antifungal activity (MIC 30-100 g/mL) against various fluconazole-resistant Candida spp., but 7S-hydroxyxestospongin A was inactive.

Alkaloids↗