The phase structure of isotactic polypropylenes isothermally crystallized from the melt has been examined at different temperatures by solid-state high-resolution 13C NMR spectroscopy using VT/MAS (variable temperature/magic angle spinning). On the basis of 13C spin-lattice relaxation and computer line-shape analyses, it has been found that polypropylene samples are composed of not only crystalline and amorphous components but also another noncrystalline component with 31-helical conformation. Similar NMR analyses at different temperatures have revealed that a reversible structural change between the 31-helical and random conformations occurs in the noncrystalline region at 60-110 "C.
We have investigated the effects of isoflurane on receptor-operated Ca2+ channels (ROC) in vascular smooth muscle. In isolated rat thoracic aortic rings denuded of endothelium, the effects of isoflurane on phenylephrine-induced contraction and Ca2+ influx were evaluated in the presence of supramaximal doses of nifedipine or verapamil. Under isometric tension recording, the aortic rings were precontracted by phenylephrine 300 nmol litre-1 and exposed to 1.2%, 2.3% or 3.5% isoflurane. Phenylephrine-induced precontraction was enhanced with 2.3% isoflurane by mean 8.1 (SD 9.3)% (P < 0.05 vs 0% isoflurane). The constrictor effect of 2.3% isoflurane was not inhibited by depletion of intracellular Ca2+ stores with ryanodine 20 mumol litre-1, but was abolished in a Ca(2+)-free solution or by SK&F 96,365 30 mumol litre-1, an ROC blocker. Isoflurane-induced contraction was accompanied by increased intracellular free Ca2+ concentration, monitored using fura PE3. Unidirectional 45Ca2+ influx measurement in phenylephrine-stimulated aortic strips revealed that the mean amount of Ca2+ influx was significantly (P < 0.05) enhanced by 1.2% and 2.3% isoflurane, which were 117.1% and 119.7% of control values, respectively. Our results strongly suggest that isoflurane enhanced Ca2+ influx through ROC that had been submaximally activated by phenylephrine.
The membrane fragments of bullfrog skeletal muscle fibers were isolated by a modification of the method of Kono and Colowick (1961). Radiocalcium ions were bound to these isolated membrane fragments, and the binding of calcium ions was impeded by both sodium and potassium ions. The extractable portion of the isolated membrane fragments with chloroform-methanol mixture bound calcium ions whereas no appreciable binding of calcium ions was observed with the extracted residue. The results suggested that the binding of calcium ions takes place on the lipid or lipoprotein of the so-called cytoplasmic membrane which plays an important role in regulating the membrane permeability and the membrane potential.
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