In order to study the dynamics of gap junctions in living cells, a cDNA was expressed in hepatocellular carcinoma-derived PLC cells coding for chimerical polypeptide Cx.EGFP-1, which consists of rat connexin32 and enhanced green fluorescent protein (EGFP). Cx.EGFP-1 was integrated into gap junctions, and the emitted epifluorescence reliably reported the distribution of the chimera. Therefore, stably transfected PLC clone PCx-9 was used to examine the dynamic behavior of gap junctions by time-lapse fluorescence microscopy. The pleomorphic fluorescent junctional plaques were highly motile within the plasma membrane. They often fused with each other or segregated into smaller patches, and fluctuation of fluorescence was detected within individual gap junctions. Furthermore, the uptake of junctional fragments into the cytoplasm of live cells was documented as originating from dynamic invaginations that form long tubulovesicular structures that pinch off. Endocytosis and subsequent lysosomal degradation, however, appeared to contribute only a little to the rapid gap junction turnover (determined half-life of 3.3 h for Cx.EGFP-1), since most cytoplasmic Cx.EGFP-1 fluorescence did not colocalize with the endocytosed fluid phase marker horseradish peroxidase or the receptor-specific endocytotic ligand transferrin and since it was distinct from lysosomes. Disassembly of gap junctions was monitored in the presence of the translation-inhibitor cycloheximide and showed increased endocytosis and continuous reduction of junctional plaques. Highly motile cytoplasmic microvesicles, which were detectable as multiple, weakly fluorescent puncta in all movies, are proposed to contribute significantly to gap junction morphogenesis by the transport of small subunits between biosynthetic, degradative, and recycling compartments.

Oligo(para-phenylene)s (DAOPPs) 2a -2d (n ¼ 1 -4) with terminal donor -acceptor substitution (D ¼ C 6 H 13 O, A ¼ NO 2 ) were prepared by applying Suzuki cross-couplings for chain extension and end capping. The push -pull effect induces short-reaching polarizations of the chain consisting of conjugated but twisted benzene rings, which was studied by NMR measurements. Electron excitation from the ground-state S 0 to the more planar first-excited singlet state S 1 is combined with a strong intramolecular charge transfer (ICT), which is documented by the red shift of the long-wavelength absorption (chargetransfer band) for short chains (one or two repeat units, n ¼ 1 or 2). The opposite influence of decreasing ICT and increasing conjugation length leads to a bathochromic series (l max (n þ 1) ! l max (n)) with a fast saturation of l max (n). The effective conjugation length n ECL ¼ 4 corresponds to l 1 349 nm. These results are discussed in the context of other oligo(para-phenylene)s (OPPs).

No abstract

Methacrylates (¼ 2-methylpropenoates) 5 with (E)-stilbene (¼ (E)-1,2-diphenylethene) building blocks on tethers of variable length were prepared (Scheme 2) and polymerized (i.e., 5 ! 6; Scheme 3) in the presence of AIBN (¼ 2,2'-azobis(2-methylpropanenitrile). 4-[(E)-2-Phenylethenyl]phenyl acetate (7) as model compound established the cyclodimerization as a single irreversible photoreaction. i.e., (7 ! 8 -11; Scheme 4) in the absence of oxygen. The solution photolysis of the polymers 6 provided a similar result, whereby [2p þ 2p] cycloadditions of stilbene units of neighboring tethers predominated. On the contrary, the desired photo-cross-linking of chaines occurred in the irradiation of polymer films.