The difference between the dissolved-solids concentration in base flow and in storm flow has often been used as the basis for separating components of flow. However, an analysis that explicitly relates the amount of time that runoff water has been in contact with watershed soils to the resulting dissolved-solids concentration shows that simple mass balance chemistry methods for hydrograph separation are misleading. Field studies of surface and subsurface storm flow, when coupled with laboratory determination of the relationship between contact time and dissolved solids content of a soil water mixture, guggest that the residence time of infiltrated water is as short as a few hours in the cases studied. In those cases, hydrograph separation methods based on the simple mass balance equation for the dissolved solids will yield considerable overestimates of the base flow component.

Connexins (Cx) 40 and 43 are coexpressed by several cell types at ratios that vary as a function of development, aging, and disease. Because these connexins form heteromeric channels, changes in expression ratio might be expected to significantly alter the connexin composition of the gap junction channel population and, therefore, gap junction function. To examine this possibility, we stably transfected A7r5 cells, which naturally coexpress Cx43 and Cx40, with a vector encoding antisense Cx43. Cx43 mRNA continued to be expressed in the antisense transfected clones, although levels were inversely related to the number of copies of antisense DNA incorporated into the genome. Protein levels, quantified in the clones with the highest and lowest Cx43:Cx40 mRNA ratios, were not well predicted by the mRNA levels, although the trends predicted by the Cx43:Cx40 mRNA ratio were preserved. Electrical coupling did not differ significantly between clones, but the clone with elevated Cx43:Cx40 protein expression ratio and unchanged Cx43 banding pattern was significantly better dye coupled than the parental A7r5 cells. These results suggest that as the Cx43:Cx40 ratio increases, provided alterations of Cx43 banding pattern (phosphorylation) have not occurred, permeability to large molecules increases even though electrical coupling remains nearly constant.

In atherosclerosis and hypertension, vascular smooth muscle cells (SMCs) are stimulated to proliferate and exhibit enhanced gap junction protein expression. Our goal was to determine whether gap junction function differs in proliferating vs. growth-arrested SMCs. A7r5 cells (embryonic rat aortic SMCs) did not proliferate in media with reduced serum (∼90% of cells in G0/G1phase after 48–96 h in 1% fetal bovine serum). Dye coupling was less but electrical coupling was comparable in proliferating vs. growth-arrested A7r5 cells, suggesting differences in junctional permselectivity. In growth-arrested cells, junctional conductances measured with potassium glutamate, tetraethylammonium chloride, and KCl were well predicted by the conductivities of these solutions. In contrast, junctional conductances measured with potassium glutamate and tetraethylammonium chloride in proliferating cells were significantly greater than predicted by the conductivities of these solutions. These results suggest that junctions between growth-arrested cells are permeated equally well and simultaneously by anions and cations, whereas junctions between proliferating cells are poorly permeated by large molecules of either charge and equally well but not simultaneously by small anions and cations. The data indicate that A7r5 cells regulate chemical coupling independent of electrical coupling, a capacity that could facilitate growth control while protecting vasomotor responsiveness of vessels.

No abstract

No abstract