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1 It is well known that extracellular ATP (ATPo) elevates the intracellular Ca2+ concentration ([Ca2+]i) by inducing Ca2+ influx or mobilizing Ca2+ from internal stores via activation of purinoceptors in the plasma membrane. This study shows that ATPo also activates the plasma membrane Ca2+ pumps (PMCPs) to bring the elevated [Ca2+]i back to the resting level in human embryonic kidney-293 (HEK-293) cells. 2 The duration of ATPo-induced intracellular Ca2+ transients was significantly increased by PMCP blockers, La3+ or orthovanadate. In contrast, replacement of extracellular Na+ with NMDG+, a membrane-impermeable cation, had no significant effect on duration, thus suggesting that Na+, a2+ exchangers do not participate in the ATPo-induced Ca2+ transient. 3 A rapid and significant decrease in [Ca2+]i, which was not dependent on extracellular Na+, was induced by ATPo in cells pretreated with thapsigargin (TG). This decrease was blocked by orthovanadate, indicating that it was caused by PMCPs rather than sarco/endoplasmic reticulum Ca2+ pumps (SERCPs). 4 UTP and ATPγS also caused a decrease in [Ca2+]i in cells pretreated with TG, although they were less effective than ATP. The effect of UTP implies the involvement of both P2Y1 and P2Y2 receptors, while the effect of ATPγS implies no significant role of ectophosphorylation and agonist hydrolysis in the agonist-induced [Ca2+]i decreases. 5 These results point to a role of PMCPs in shaping the Ca2+ signal and in restoring the resting [Ca2+]i level to maintain intracellular Ca2+ homeostasis after agonist stimulation. British Journal of Pharmacology (2000) 131, 370 – 374

The annealing effects of block and graft copolymer membranes consisting of ethanol-permselective poly(dimethylsiloxane) (PDMS) plus water-permselective poly(methyl methacrylate) (PMMA) on their permselectivity for an aqueous ethanol solution in pervaporation were investigated in terms of their microphase separation. The ethanol-permselectivity of the block copolymer membranes was strongly influenced by the annealing, but that of the graft copolymer membranes was not. The original block copolymer membranes changed from water- to ethanol-permselectivity at a DMS content of 55 mol %, but the annealed block copolymer membranes changed at a DMS content of 37 mol %. Transmission electron micrography demonstrated that the annealing of the block copolymer membranes with a DMS content between 37 and 55 mol % resulted in dramatic changes in the morphology of their microphase separation. However, the annealing of the graft copolymer membranes had very little effect on the morphology of their microphase separation, which was quite different from the morphology of the block copolymer membranes. The analysis using a combined model consisting of parallel and series models revealed that a continuous PDMS phase in the direction of the membrane thickness is readily formed by the annealing of the block copolymer membranes. As a result, the continuity of the PDMS phase in the microphase separation governed the ethanol-permselectivity of these membranes for an aqueous ethanol solution. This report concludes that the morphological design of microphase-separated membranes, which can be achieved by membrane annealing, is very important in controlling their permeability and permselectivity.

The permselectivity of block copolymer membranes consisting of ethanol-permselective poly(dimethylsiloxane) (PDMS) plus water-permselective poly(methyl methacrylate) (PMMA) was compared to the permselectivity of graft copolymer membranes for the separation of an aqueous ethanol solution. This paper focuses on the difference in molecular architecture between the block and graft copolymers and relates microphase separation in these membranes to their permeability and permselectivity for an aqueous ethanol solution in pervaporation. With increasing DMS content, the block copolymer membranes changed from water- to ethanol-permselective at a DMS content of 55 mol %. As reported in a previous paper, however, the graft copolymer membranes showed a dramatic change in the permselectivity at a DMS content of 35 mol %. Transmission electron micrography demonstrated that both membranes had distinct microphase separation consisting of PDMS and PMMA phases and that the morphology was quite different between the block and graft copolymer membranes. The morphological changes in these membranes were investigated by image processing of the micrographs and analysis using a combined model consisting of both parallel and series models. These investigations revealed that the percolation transition of the PDMS phase in the block and graft copolymer membranes takes place at a DMS content of about 55 and 35 mol %, respectively. This suggests that the continuity of the PDMS phase in the microphase separation strongly influences the ethanol permselectivity of these membranes for an aqueous ethanol solution. This report concludes that the design of the molecular architecture in multicomponent polymer membranes is very important in controlling membrane characteristics which are governed by microphase separation.

The genes encoding two dissociable components essential for Bacillus stearothermophilus heptaprenyl diphosphate synthase (all-trans-hexparenyl-diphosphate:isopentenyl-diphosphate hexaprenyl-trans-transferase, EC 2.5.1.30) were cloned, and their nucleotide sequences were determined. Sequence analyses revealed the presence of three open reading frames within 2,350 base pairs, designated as ORF-1, ORF-2, and ORF-3 in order of nucleotide sequence, which encode proteins of 220, 234, and 323 amino acids, respectively. Deletion experiments have shown that expression of the enzymatic activity requires the presence of ORF-1 and ORF-3, but ORF-2 is not essential. As a result, this enzyme was proved genetically to consist of two different protein compounds with molecular masses of 25 kDa (Component I) and 36 kDa (Component II), encoded by two of the three tandem genes. The protein encoded by ORF-1 has no similarity to any protein so far registered. However, the protein encoded by ORF-3 shows a 32% similarity to the farnesyl diphosphate synthase of the same bacterium and has seven highly conserved regions that have been shown typical in prenyltransferases (Koyama, T., Obata, S., Osabe, M., Takeshita, A., Yokoyama, K., Uchida, M., Nishino, T., and Ogura, K. (1993) J. Biochem. (Tokyo) 113, 355-363).