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201 records · Page 12Linked to original sources
PubMed1988

The biogeochemical cycle of the adsorbed template. II: Selective adsorption of mononucleotides on adsorbed polynucleotide templates.

Experimental results are presented for the verification of the specific interaction step of the 'adsorbed template' biogeochemical cycle, a simple model for a primitive prebiotic replication system. The experimental system consisted of gypsum as the mineral to which an oligonucleotide template attaches (Poly-C or Poly-U) and 5'-AMP, 5'-GMP, 5'-CMP and 5'-UMP as the interacting biomonomers. When Poly-C or Poly-U were used as adsorbed templates, 5'-GMP and 5'-AMP, respectively were observed to be the most strongly adsorbed species. Moreover, there exists a direct quantitative relationship between the quantity of cytidine or uracil residues in the adsorbed state and the amount of the complementary mononucleotide that is attached to it. NaCl added to the system in order to create conditions of high ionic strength seems to enhance the selectivity of the adsorption of the monmucleotides to these adsorbed templates.

Adsorption↗
PubMed1996

Up-regulation of endothelin-B receptors in atherosclerotic human coronary arteries.

Both endothelin-A (ETA) and endothelin-B (ETB) receptors are known to be present in human coronary arteries. However, their absolute and relative amounts, functional roles, and the influence of pathology are uncertain. The goal of the present study was to characterize endothelin receptors mediating constriction in human coronary arteries and to assess the influence of cardiomyopathy (CMP) and coronary artery disease (CAD) on ET receptors in human tissue. For comparison, porcine coronary arteries were evaluated in parallel. Competition binding experiments using [125I]ET-1 and different selective and nonselective ETA- and ETB-receptor agonists or antagonists revealed similar relative densities (relative Bmax) of ETA and ETB receptors in coronary arteries from human cardiomyopathic hearts (83% ETA and 17% ETB; n = 5) and porcine hearts (78% ETA and 22% ETB; n = 5). In marked contrast, the relative Bmax of ETB receptors were significantly higher in coronary arteries from human atherosclerotic hearts (51% ETA and 49% ETB; n = 3). Total receptor density (Bmax; fmol/mg protein) was highest in porcine (385 +/- 29) arteries, followed by human CAD (253 +/- 41) and CMP (174 +/- 20) coronary arteries. The relative and absolute Bmax values for ETA and ETB receptors in coronary arteries from a donor heart were similar to those obtained in CMP hearts. There were no significant differences in affinity constants (KD) values for ET-1, ET-3, Sarafotoxin S6c (SRTX S6c), BQ-123, and bosentan (Ro 47-0203) between tissues. In human coronary arteries from CMP hearts, ET-induced constriction seemed to be solely mediated via ETA receptors. In contrast, in porcine coronary arteries 20% of the maximal effect mediated by ET-1 could be attributed to ETB receptors, in agreement with the binding data. The functional role of ETB receptors in CAD tissue could not be evaluated because of the occurrence of spontaneous phasic contractions. We conclude that ETB receptors are up-regulated in human atherosclerotic coronary arteries. Further studies are needed to determine the pathophysiological importance of these receptors.

Acetylcholine↗
PubMed2002

Adenosine 5'-monophosphate is a selective inhibitor of the brown adipocyte nonselective cation channel.

Calcium-activated nonselective cation channels (NSC(Ca)) in brown adipocytes are inhibited by several nucleotides acting on the cytosolic side of the membrane. We used excised inside-out patches from rat brown adipocytes to identify important nucleotide structures for NSC-channel inhibition. We found that 100 microM 5'-AMP inhibited NSC-channel activity more than did ATP or ADP. Adenosine was a weak inhibitor, whereas adenine and ribose-5-phosphate had no effect. The channel activity was effectively blocked by 10 microM AMP, but it was unaffected by 10 microM cAMP, CMP, GMP, IMP, TMP or UMP. Dose-response studies yielded IC(50)-values of 4 microM for AMP and 32 microM for cAMP. dAMP was as effective as AMP, but all 5'-phosphate group modifications on AMP dramatically lowered the inhibitory effect. 10 microM of the AMP precursor adenylosuccinate weakly inhibited the channel activity. An increase in AMP concentration from 1 to 10 microM shifted the EC(50) for Ca(2+) activation almost 1 order of magnitude; a Schild plot analysis yielded a K(B) value of 0.3 microM for AMP. We conclude that AMP is the most efficacious endogenous nucleotide inhibitor of the brown adipocyte nonselective cation channel (NSC(Ca/AMP)) yet identified and that there is functional competition between Ca(2+) and AMP. The brown adipocyte NSC(Ca/AMP) thus appears to be functionally different from the NSC(Ca,PKA) in the exocrine pancreas and the NSC-(Ca,cAMP) in the endocrine pancreas, but similar to the NSC(Ca/AMP) in the endocrine pancreas.

Adenosine Monophosphate↗