The UT-A (SLC14a2) and UT-B (SLC14a1) genes encode a family of specialized urea transporter proteins that regulate urea movement across plasma membranes. In this report, we describe the structure of the bovine UT-B (bUT-B) gene and characterize UT-B expression in bovine rumen. Northern analysis using a full-length bUT-B probe detected a 3.7-kb UT-B signal in rumen. RT-PCR of bovine mRNA revealed the presence of two UT-B splice variants, bUT-B1 and bUT-B2, with bUT-B2 the predominant variant in rumen. Immunoblotting studies of bovine rumen tissue, using an antibody targeted to the NH2-terminus of mouse UT-B, confirmed the presence of 43- to 54-kDa UT-B proteins. Immunolocalization studies showed that UT-B was mainly located on cell plasma membranes in epithelial layers of the bovine rumen. Ussing chamber measurements of ruminal transepithelial transport of (14)C-labeled urea indicated that urea flux was characteristically inhibited by phloretin. We conclude that bUT-B is expressed in the bovine rumen and may function to transport urea into the rumen as part of the ruminant urea nitrogen salvaging process.

On each of a 4-month series of weekly cruises in Kaneohe Bay, Oahu, Hawaii, irr cico chlorophyll a was monitored continuously by fluorometry, and at 8 stations discrete measurements of chlorophyll a ( trichromatic method), primary productivity ("C ), and nutrients (nitrate and phosphate) were made. The results are compared with similar data collected a decade earlier in the bay to investigate the enrichment effects of increased waste discharge over this period. The south sector of the bay, site of two sewage outfalls, showed the greatest population instability and had the highest concentrations of chlorophyll a, nitrate, and phosphate, as well as the highest primary productivity.Chlorophyll, nutrient concentration, and primary productivity decreased through the transition sector into the north sector of the bay, which is farthest removed from the waste discharge points. The productivity index (mg C fixed hr-l mg Chl a-l) showed no such south to north differences. A model of a simplified food chain using a hyperbolic relationship between uptake rate and substrate concentration is postulated to explain the dynamics of the plankton community in the bay.

The seasonal cycle of vitamin B12 in the Strait of Georgia, British Columbia, was studied over a 17-month period. The temporal and spatial distribution of this vitamin was found to be more complex than that of nitrate and phosphate in the Strait and B12 reported for other areas.The vitamin data are compared with inorganic nutrient distributions and physical characteristics of the Strait of Georgia to support the hypothesis that the observed heterogeneity of B12 is largely the result of vitamin–particulate matter interactions.

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