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J R Guerrero

Publications and source records attributed to J R Guerrero.

9 recordsLinked to original sources
PubMed2000

Labeling the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum with maleimidylsalicylic acid.

Maleimidylsalicylic acid reacts with the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum with high affinity and inhibits the ATPase activity following a pseudo-first-order kinetic with a rate constant of 8.3 m(-1) s(-1). Calcium binding remains unaffected in the maleimide-inhibited ATPase. However, the presence of ATP, ADP, and, to a lesser extent, AMP protects the enzyme against inhibition. Furthermore, ATPase inhibition is accompanied by a concomitant decrease in ATP binding. The stoichiometry of the nucleotide-dependent maleimidylsalicylic acid binding is 6-10 nmol/mg ATPase, which corresponds to the binding of up to one molecule of maleimide/molecule of ATPase. The stoichiometry of maleimide binding is decreased in the presence of nucleotides and in the ATPase previously labeled with fluorescein-5'-isothiocyanate or N-ethylmaleimide A fluorescent peptide was isolated by high performance liquid chromatography after trypsin digestion of the maleimide-labeled ATPase. Analysis of the sequence and mass spectrometry of the peptide leads us to propose Cys(344) as the target for maleimidylsalicylic acid in the inhibition reaction. The effect of Cys(344) modification on the nucleotide site is discussed.

Adenosine Diphosphate↗
PubMed1985

Isomers of long-chain alkane derivatives and nervous impulse blockage.

The potency to block nervous impulse of members of normal aliphatic homologous series of primary and secondary isomers of functional derivatives of alkanes was tested in bundles of a few axons from sciatic nerves of the toad Bufo marinus. For the primary substituted functional derivates of pentane, the relative potency series was I greater than H approximately equal to Br greater than Cl greater than COOCH3 greater than F greater than CH2OH greater than COCH3 greater than OH approximately equal to NH2 greater than COOH. For the homologous series of primary alkanols, and from saturated Ringer's solutions, the time required to reversibly reduce the amplitude of the action potential to one-half its initial value were determined. The cut-off effect was detected at the level of dodecan-1-ol, while for the primary bromoalkanes it was bromooctane. However, solutions of the secondary isomer of the inactive primary homologues, such as tridecan-5-ol and tridecan-7-ol or 2-bromononane, were able to block nervous impulse conduction reversibly. From the concentration required for an equipotent effect it was calculated that the standard free energy for adsorption of primary alkanols was -705 cal mol- CH2. Similarly, for primary bromoalkanes a value of -733 cal mol-1 CH2 was obtained. The concentration required for an equipotent effect for primary isomer (either of alkanols or bromoalkanes) is lower than those obtained for the secondary isomers. Therefore, the latter are less potent than the former. Among secondary isomers the potency decreases as the functional group is moved away from the terminal carbon. The differential effect of structural isomers of long-chain alkane derivates around the point of cut-off cannot be explained in terms of differences in chemical properties, concentration in aqueous and membrane phases, or mean molecular volume. It is concluded that a volume related to that of the hydrophobic region of the agent and not its mean molecular volume should be responsible for an expansion of the target region.

Alcohols↗
PubMed1981

Short-term efficacy of oral verapamil in rest angina. A double-blind placebo controlled trial in CCU patients.

To determine the efficacy and safety of oral verapamil in patients with rest angina admitted to the Coronary Care Unit (CCU), a double-blind placebo-controlled trial was undertaken. Of the 65 patients with rest angina screened for the study, 15 met the inclusion criteria (at least two episodes of chest pain associated with ST-T segment changes per 24 hours) during single-blind placebo phase (Day 1). Patients were then randomized to receive either placebo or verapamil (80 mg every 6 hours) on Day 2. Protocol was designed such that those who did not respond to the placebo (nonresponders) received verapamil, 80 mg every 6 hours, whereas verapamil nonresponders received increased doses (120 mg every 6 hours) on Day 3. Those who did respond (responders) continued to receive their medication. Similar action was taken on Day 4, depending on chest pain frequency and clinical evaluation. The study drug was unblinded on Day 4. At the end of the four-day period, 13 patients were receiving verapamil (nine patients, 80 mg every 6 hours, and four patients, 120 mg every 6 hours) and all but one were responders. One patient received placebo all through the period of the study and was also considered to be a responder. In the remaining one patient evidence of myocardial necrosis developed after he received a single dose of verapamil (80 mg on Day 2). Except for the prolongation of PR interval in two patients while taking verapamil, no side effects from verapamil therapy were observed. These data demonstrate the efficacy of oral verapamil in reducing episodes of myocardial ischemia in the majority of all patients with rest angina.

Administration, Oral↗
PubMedDate not supplied

Verapamil: full spectrum calcium channel blocking agent: an overview.

Oral verapamil approved for use in all forms of angina, with its additional heart rate-controlling properties has undergone extensive clinical investigation and use since its initial development and has been demonstrated to be safe, well-tolerated and effective over a broad range of cardiovascular disorders. Further potential therapeutic indications for verapamil use remain to be assessed. Additional research with this exciting drug is ongoing.

Calcium↗
PubMedDate not supplied

Direct visualization of myosin filament symmetry in tarantula striated muscle by electron microscopy.

Chemically demembranated bundles of fibers from tarantula leg muscle were rapidly frozen in the relaxed state and freeze-substituted in the presence of tannic acid. Electron micrographs of thin transverse sections of freeze-substituted specimens frequently showed four clear, regularly organized projections (crossbridges) protruding from the backbones of the myosin filaments and partially wrapping around the filament surface. The rotational power spectra of individual filaments showed a peak at N = 4. Alignment and averaging of the images using correlation methods confirmed the fourfold symmetry and the slewed configuration of the crossbridges on the filament surface. These observations directly reveal essential features of the low-resolution three-dimensional helical reconstruction of negatively stained tarantula filaments calculated previously (R. A. Crowther, R. Padrón, and R. Craig, 1985, J. Mol. Biol. 184, 429-439).

Animals↗
PubMedDate not supplied

Three-dimensional reconstruction of thick filaments from rapidly frozen, freeze-substituted tarantula muscle.

We have applied three-dimensional helical reconstruction techniques to images of myosin filaments of tarantula leg muscle obtained from rapidly frozen, freeze-substituted specimens. Computed Fourier transforms of filaments selected from longitudinal sections show up to six layer lines indexing on the 43.5-nm helical repeat of myosin crossbridges. The three-dimensional reconstruction, performed after separation of overlapped Bessel functions, shows four continuous strands of density on the surface of the filament, modulated by density at 14.5-nm intervals, corresponding to the myosin heads aligned approximately along the helical strands. In transverse viw, the reconstruction shows four projections and is similar in profile to myosin filaments seen in thin transverse sections of rapidly frozen muscle. The reconstruction is similar to that of negatively stained, isolated tarantula filaments except that in the latter there is an additional modulation of the helix density, which better resolves the two heads of each myosin crossbridge. Thus, the general arrangement of the myosin heads in the freeze-substituted specimens is preserved, although finer details of structure such as individual myosin heads are lost.

Actin Cytoskeleton↗
PubMedDate not supplied

Visualization of myosin helices in sections of rapidly frozen relaxed tarantula muscle.

Tarantula leg muscles in the relaxed state were rapidly frozen against a copper block cooled with liquid helium. Thin longitudinal sections of freeze-substituted specimens, both live and skinned, clearly showed the helical tracks of crossbridges on the surface of the myosin filaments, which are not preserved by conventional fixation. Fourier transforms of selected filaments showed a myosin layer line pattern, similar to that observed in X-ray diffraction patterns of intact tarantula muscle, extending to the sixth order of the 43.5 nm X-ray repeat. The phases of corresponding reflections were similar on the two sides of the meridian on the first layer line, and the crossbridge arrangement showed a line of mirror symmetry running down the center of the filament. These observations show that the number of helices (N) is even, in agreement with N = 4 determined from image analysis of negatively stained, isolated tarantula filaments (Crowther et al., J. Mol. Biol. 184, 429-439, 1985). Filtered images showed clear detail of the crossbridge helices and were similar to filtered images of negatively stained, isolated thick filaments. Thus, rapid freezing combined with freeze-substitution preserves the crossbridges in a three-dimensional arrangement approximating that occurring in vivo.

Animals↗