Highly crystalline, well-developed hydroxyapatite (HAp) crystals were grown successfully for the first time by a flux cooling method at a temperature less than 500 °C under air pressure. Environmentally friendly growth was induced by heating a mixture of solute [Ca(NO 3 ) 2 • 4H 2 O, (NH 4 ) 2 HPO 4 , and KOH] and flux (KNO 3 and LiNO 3 ) at 400-500 °C and holding at this temperature for 10 h. After that, the mixture was cooled at various rates of 5, 200, and >1000 °C • min -1 (water quenching). The obtained HAp crystals, which had average sizes of up to 18.0 × 2.1 µm and aspect ratios of up to 8.6, were colorless and transparent. They had hexagonal prismatic one-dimensional (1-D) forms with pyramidal or truncated pyramidal end faces. The 1-D crystal forms and sizes were obviously dependent on the growth conditions, such as the holding temperature and the cooling rate of the high-temperature solution. High-resolution transmission electron microscopy (HR-TEM) images indicated that the grown HAp crystals were of a very good crystallinity. From the HR-TEM and X-ray diffraction, the 1-D HAp crystals, which were hexagonal cylinders ({101 j 0} faces), elongated in the 〈0001〉 directions.
Although changes in intracellular Ca2+ concentration ([Ca2+]i) are spatially heterogeneous during spontaneous contraction in mammalian cardiac muscle, it has not yet been observed how [Ca2+]i changes spatially within cardiac myocytes during delayed (DADs) and early (EADs) afterdepolarizations. The aim of this study is to characterize the spatial features of the increase in [Ca2+]i during such afterdepolarizations and to understand the ionic mechanisms responsible for them. Myocytes were enzymatically isolated from guinea pig ventricles and loaded with fura 2-acetoxymethylester, the Ca2+ fluorescence indicator dye. Membrane potential was recorded with a conventional microelectrode technique, and spatiotemporal changes in fura 2 fluorescence and cell length were recorded using a digital television system. After superfusion with potassium-free Tyrode solution, DADs and EADs were induced. During DADs, fluorescence transients were heterogeneous within myocytes (n = 11). Furthermore, they often propagated within myocytes as if they were "waves." In contrast, during EADs, fluorescence transients showed no waves within myocytes but rather showed synchronous changes throughout the myocytes (n = 15). The results of this study suggest that the spatial features of the increase in [Ca2+]i differ between the DADs and EADs. We concluded from these differing features that the ionic mechanisms responsible for the two triggered activities are different.
Unique and characteristically formed spherulitic crystals of octacalcium phosphate (OCP, Ca8H2(PO4)6·5H2O) were grown for the first time by the gel method, using the system Ca(NO3)2−(NH4)2HPO4−agar. The shape of test tubes crucially affected the morphological development of the OCP crystals. The feature of OCP spherulites grown in U-type test tubes was an aggregation of a relatively ordered, large number of ultralong and flexible whiskers radiating from the center region of the spheres, resulting in high porosity. On the other hand, OCP crystals grown in straight test tubes were a spherulite consisting of a large number of short plate-like, well-faceted crystallites radiating from a common origin. In both cases, OCP crystals grew with spherulitic morphologies even under varied conditions of different growth parameters, including gel concentration, reactant concentration, and growth period.
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