Effects of deoxycholylglycine, a conjugated secondary bile acid, on myogenic tone and agonist-induced contraction in rat resistance arteries.

BACKGROUND: Bile acids (BAs) regulate cardiovascular function via diverse mechanisms. Although in both health and disease serum glycine-conjugated BAs are more abundant than taurine-conjugated BAs, their effects on myogenic tone (MT), a key determinant of systemic vascular resistance (SVR), have not been examined. METHODOLOGY/PRINCIPAL FINDINGS: Fourth-order mesenteric arteries (170-250 µm) isolated from Sprague-Dawley rats were pressurized at 70 mmHg and allowed to develop spontaneous constriction, i.e., MT. Deoxycholylglycine (DCG; 0.1-100 µM), a glycine-conjugated major secondary BA, induced reversible, concentration-dependent reduction of MT that was similar in endothelium-intact and -denuded arteries. DCG reduced the myogenic response to stepwise increase in pressure (20 to 100 mmHg). Neither atropine nor the combination of L-NAME (a NOS inhibitor) plus indomethacin altered DCG-mediated reduction of MT. K(+) channel blockade with glibenclamide (K(ATP)), 4-aminopyradine (K(V)), BaCl(2) (K(IR)) or tetraethylammonium (TEA, K(Ca)) were also ineffective. In Fluo-2-loaded arteries, DCG markedly reduced vascular smooth muscle cell (VSM) Ca(2+) fluorescence (∼50%). In arteries incubated with DCG, physiological salt solution (PSS) with high Ca(2+) (4 mM) restored myogenic response. DCG reduced vascular tone and VSM cytoplasmic Ca(2+) responses (∼50%) of phenylephrine (PE)- and Ang II-treated arteries, but did not affect KCl-induced vasoconstriction. CONCLUSION: In rat mesenteric resistance arteries DCG reduces pressure- and agonist-induced vasoconstriction and VSM cytoplasmic Ca(2+) responses, independent of muscarinic receptor, NO or K(+) channel activation. We conclude that BAs alter vasomotor responses, an effect favoring reduced SVR. These findings are likely pertinent to vascular dysfunction in cirrhosis and other conditions associated with elevated serum BAs.

Functional analysis of the Volvox carteri asymmetric division protein GlsA.

The Zuotin-family J protein chaperone GlsA is essential for the asymmetric divisions that establish germ and somatic cell initials during embryogenesis in the green alga Volvox carteri, but it is not known on what cellular process GlsA acts to carry out this function. Most GlsA protein is nuclear, and GlsA possesses two SANT domains, suggesting that GlsA may function as a transcriptional regulator. On the other hand, close homologs from yeast and mice are ribosome-associated factors that regulate translation fidelity, implying GlsA might also regulate translation. Here we set out to gain additional evidence regarding the function of GlsA, specifically with respect to its possible involvement in transcription and translation. We found that like zuotin mutants, glsA mutants are ultrasensitive to both cold and to the ribosome-binding aminoglycoside antibiotic paromomycin, so some fraction of GlsA is likely to be ribosome associated. We also found that GlsA co-immunoprecipitates with histones and that this interaction is dependent on the presence of intact SANT domains. Through rescue experiments using transgenes that encode GlsA variants, we determined that the growth and asymmetric division defects of the glsA mutant are separable-a GlsA variant that rescued the growth defects did not completely rescue the asymmetric division phenotype. Considered in total, our results suggest that GlsA acts both at the level of translation and transcription, but the function that is essential for tolerance to paromomycin and cold is not sufficient for asymmetric cell division.

Hsp70A and GlsA interact as partner chaperones to regulate asymmetric division in Volvox.

GlsA, a J-protein chaperone, is required for the asymmetric divisions that set aside germ and somatic cell precursors during embryogenesis in Volvox carteri, and previous evidence indicated that this function requires an intact Hsp70-binding site. To determine if Hsp70A, the only known cytoplasmic Hsp70 in V. carteri, is the chaperone partner of GlsA, we investigated the localization of the two proteins during critical stages of embryogenesis and tested their capacity to interact. We found that a substantial fraction of Hsp70A co-localizes with GlsA, both in interphase and mitotic blastomeres. In addition, Hsp70A coimmunoprecipitated with GlsA, and co-expression of GlsA and Hsp70A variants partially rescued the Gls phenotype of a glsA mutant, whereas neither variant by itself rescued the mutant phenotype. Immunofluorescence analysis demonstrated that GlsA is about equally abundant in all blastomeres at all cleavage stages examined but that Hsp70A is more abundant in anterior (asymmetrically dividing) blastomeres than in posterior (symmetrically dividing) blastomeres during the period of asymmetric division. We conclude that Hsp70A and GlsA function as chaperone partners that regulate asymmetric division and that the relative abundance of Hsp70A in asymmetrically dividing embryos may determine which blastomeres divide asymmetrically and which do not.