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Many tissues express multiple gap junction proteins, or connexins (Cx); for example, Cx43, Cx40, and Cx37 are coexpressed in vascular cells. This study was undertaken to elucidate the consequences of coexpression of Cx40 or Cx37 with Cx43 at different ratios. EcR-293 cells (which endogenously produce Cx43) were transfected with ecdysone-inducible plasmids encoding Cx37 or Cx40. Immmunoblotting showed a ponasterone dose-dependent induction of Cx37 or Cx40 while constant levels of Cx43 were maintained. The coexpressed connexins colocalized at appositional membranes. Double whole-cell patch clamp recordings showed no significant change in total junctional conductances in cells treated with 0, 0.5, or 4 μM ponasterone; however, they did show a diversity of unitary channel sizes consistent with the induced connexin expression. In cells with induced expression of either Cx40 or Cx37, intercellular transfer of microinjected Lucifer yellow was reduced, but transfer of NBD-TMA (2-(4-nitro-2,1,3-benzoxadiol-7-yl)[aminoethyl]trimethylammonium) was not affected. In cocultures containing uninduced EcR cells together with cells induced to coexpress Cx37 or Cx40, Lucifer yellow transfer was observed only between the cells expressing Cx43 alone. These data show that induced expression of either Cx37 or Cx40 in Cx43-expressing cells can selectively alter the intercellular exchange of some molecules without affecting the transfer of others. [ABSTRACT FROM AUTHOR]

Chlorophyll fluorescence parameters were measured in leaves of six plant species (barley, soybean, clover, Tradescantia, Atriplex semibacata and Atriplex patula). Plant cuttings were exposed for 24 hours tolead chloride, sodium pentachlorophenate, butadiene monoxide, beta- naphthylamine or Ortho, a commercial brand of insecticide with chlorpyrifos as an active ingredient, at 3--10 different concentrations. Barley and clover were found to be the most responsive species. Sodium pentachlorophenate was the most toxic chemical, followed by lead chloride and Ortho. Beta-naphthylamine and butadiene monoxide were shown to be less harmful. The most reliable parameters in terms of predicting the effect of tested chemical on fluorescence arc Fv/Fm, the ratioof variable fluorescence (Fv) to maximal fluorescence (Fm), Fo, initial fluorescence and t{sub}1/2{end}, half the length of time of the rise from minimal to maximal fluorescence. This conclusion is based onthe calculation of the coefficients of determination of regression for all parameters. In the presence of tested chemicals Fo increased, while Fv/Fm and t{sub}1/2{end} decreased with increasing concentration. Decline of the Fv/Fm indicates the disturbance in the functioning of the photosynthetic electron transport. The increase in Fo suggeststhe inhibition of PS II reaction center and decrease in t{sub}1/2{end} is linked to the lowering of the relative number of active PS II centers. [ABSTRACT FROM AUTHOR]