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Excess partial molar enthalpies, H,~, of methanol, ethanol, and 1-and 2-propanols in aqueous solutions were measured directly, accurately, and in small increments in mole fraction at 25OC. From these data, the solute-solute enthalpic interactions, HAAE = N(aHAE1a~zA), were evaluated for each alcohol. These data indicate that three distinctively different mixing schemes, I, 11, and I11 exist, as was the case for aqueous 2-butoxyethanol previously studied in our laboratory. The transition from mixing scheme I to I1 appears to take place gradually within a small composition range. As the hydrophobic moiety becomes smaller from 2-butoxyethanol to methanol, the locus of the transition moves to a higher value in mole fraction of the alcohol. At the same time, the range of transition becomes wider and the solute-solute enthalpic interaction weaker.Key words: excess partial molar enthalpies in aqueous solutions, methanol, ethanol, I-propanol, 2-propanol, enthalpic interaction, transition of mixing scheme. Ces donnCes suggkrent l'existence de trois schCmas diffirents de mClanges, I, I1 et 111, comme ce ftit le cas pour le 2-butoxyCthanol CtudiC antkrieurement dans notre laboratoire. I1 semble que la transition du schCma de melange I vers I1 se produit graduellement, B I'intCrieur d'une faible plage de composition. Quand les portions hydrophobes deviennent plus petites en allant du 2-butoxyCthanol vers le mCthanol, le foyer de la transition se dCplace vers des valeurs plus ClevCs de la fraction molaire de l'alcool. En m&me temps, l'intervalle de transition devient plus grand et l'interaction enthalpique solutC-solutC devient plus faible.Mors clis : enthalpies molaires partielles en excks en solutions aqueuses, mCthanol, ethanol, propan-1-01, propan-2-01, interaction enthalpique, schCma de transition de melange.

In a freshly isolated endothelial cell preparation from rabbit aorta, the regulation of the acetylcholine (ACh)-sensitive intracellular Ca2+ store and the effects of the Ca(2+)-induced Ca2+ release agonists ryanodine and caffeine were studied using fura 2 imaging fluorescence microscopy. ACh (10 mumol/L) caused a transient release of Ca2+ from an intracellular store, presumably via an inositol tris-phosphate-sensitive mechanism. This ACh response could be repeated in the presence of extracellular Ca2+ but was obtained only once in Ca(2+)-free bathing solution, which shows that a depleted intracellular Ca2+ store can be rapidly refilled from the extracellular space. Refilling can be prevented by the endoplasmic reticulum Ca(2+)-ATPase inhibitor cyclopiazonic acid (10 mumol/L), implying that Ca2+ enters the cytoplasm before accumulation in the endoplasmic reticulum. Ionomycin (10 mumol/L) caused a large Ca2+ release even after the ACh-releasable store had been emptied, indicating the existence of other ACh-insensitive stores, perhaps including the mitochondria. In one third of the cells studied, ACh induced oscillations in [Ca2+]i that were dependent on extracellular Ca2+. Also investigated were the effects of caffeine and ryanodine. In this cell preparation neither caffeine nor ryanodine induced a Ca2+ transient but instead slowly increased [Ca2+]i. It was observed that both caffeine and ryanodine were able to slowly deplete the ACh-sensitive store. These results indicate the presence of functional ryanodine receptors in native endothelial cells and demonstrate overlap between the caffeine and agonist-sensitive Ca2+ stores. We also found that caffeine was able to directly inhibit the process of ACh-induced Ca2+ release.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermal expansivities of aqueous solutions of 2-butoxyethanol (BE) were measured at concentrations of x,, < 0.04, where xBE is the mole fraction of BE. Thermal expansivity is a second derivative of the Gibbs free energy. The composition derivatives of thermal expansivities, the third derivatives, show peak anomalies at the same loci as the other third derivatives of the Gibbs free energy reported earlier from this laboratory (Can. J. Chem. 67, 671 (1989); J. Phys. Chem. 94, 3879 (1990); J. Phys. Chem. 95, 41 19 (1991)). The loci of such anomalies form a boundary that separates two regions of totally different mixing schemes. The mixing scheme in the water-rich region seems to be consistent with the "iceberg formation," the "structure enhancement of H 2 0 by hydrophobic solute," and the "hydrophobic attraction." In the intermediate composition region, the hydrogen bond network of H 2 0 collapses due to the presence of too many molecules of BE, and H,O and BE molecules interact with each other as normal liquid molecules.

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