The present study determined the presence of two types of binding sites for atrial natriuretic factor (ANF), the B and C receptor, on rat glomerular membranes. The effect of short-term salt loading and dehydration on these two receptor populations was investigated consecutively. Salt-loaded rats did not show significant changes in plasma ANF concentrations or in the number of ANF binding sites. Water-deprived rats presented significantly lower plasma ANF concentrations (22.0 +/- 1.9 vs. 34.4 +/- 3.8 fmol/ml, P less than 0.01) and an increase in total receptor density (1,860 +/- 398 vs. 987 +/- 143 fmol/mg protein) as compared with the control group. Differentiation of both receptor populations showed that it was the C receptors that accounted for this increase (1,772 +/- 369 vs. 901 +/- 151 fmol/mg protein, P less than 0.05), whereas B-receptor density was unchanged (89 +/- 31 vs. 87 +/- 44 fmol/mg protein). These data suggest that C receptors for ANF are affected by changes of body fluid volume.

Dedicated to Professor Wolfram Zillig on the occasion of his 60th birthdayThe lipophilic antibiotic rifampicin is successfully used in the treatment of tuberculosis. On the molecular level it interferes with the metabolism of Eubacteria by blocking RNA synthesis. This effect is the consequence of the tight binding of the drug to a single and highly specific binding site on the DNA-dependent RNA polymerase. The enzyme-bound drug strongly inhibits RNA chain initiation and chain elongation. This inhibition can be explained by the influence of enzyme-bound rifampicin on binding sites for the reaction products diphosphate and RNA. In order to reach its target the antibiotic must penetrate into the cytoplasm of the bacteria. Mutants have been discovered which are resistant to rifampicin because its uptake from the medium is significantly reduced. The gene responsible for this effect has been cloned. It confers on bacterial cells with highly sensitive RNA polymerases a remarkable resistance to the drug.

No abstract

Switzerland; 4University of Rochester, Rochester, New York 14642; and 5 C~r Therapeutics, Inc., South Sun Francisco, California 94080The renal response to atrial natriuretic factor is blunted in cirrhosis with ascites. This might be due to alterations of renal receptors for atrial natriuretic factor. Therefore density and affinity of glomerular atrial natriuretic factor binding sites of bile ductligated rats with ascites (n = 10) and of sham-operated controls (n = 10) were determined. Glomerular atrial natriuretic factor binding sites were identified to be of the B-("biologically active") and C-("clearance") receptor type. Discrimination and quantitative determination of B and C receptors for atrial natriuretic factor were achieved by displacement experiments with atrial natriuretic factor(99-126) or des(l8-22)atrial natriuretic factor(4-23), an analogue binding to C receptors only. Density of total glomerular atrial natriuretic factor binding sites was significantly increased in bile duct-ligated rats (3,518 * 864 vs.1,648 2 358 fmol/mgprotein; p < 0.05). This was due to a significant increase of C-receptor density (3,460 f 866 vs. 1,486 f 363 fmol/mg protein; p < 0.05), whereas density of B receptors was not significantly different in bile duct-ligated rats (58 2 11 vs. 162 2 63 fmol/mg protein). Affinity of atrial natriuretic factor to its glomerular binding sites did not differ significantly between both groups. These data suggest that an altered glomerular atrial natriuretic factor receptor density could be involved in the renal resistance to atrial natriuretic factor in cirrhosis with ascites. (HEPATOLOCY 1991;13:562-566 Renal response to ANF has been shown to be blunted in patients with cirrhosis and in rat models of cirrhosis (14-21). This renal resistance to circulating and to exogenously administered ANF in cirrhosis might be due to an alteration of ANF receptor density. Therefore in this study we investigated both types of ANF binding sites in renal glomeruli of cirrhotic rats. MATERIALS AND METHODSAnimals. Male Sprague-Dawley rats (300 to 320 g m ) were subjected to bile duct ligation and division (22). In the control group, animals were sham-operated with visualization of the bile duct. The rats were fed with regular pelleted chow and tap 562

A new class of rifamycin-resistant mutants of Escherichia coli was obtained by lysogenic insertions of bacteriophage Mu Amp DNA. Rifamycin resistance is closely linked to the ampicillin resistance conferred by the prophage. Mapping by conjugation with auxotrophic markers revealed that the rifamycin-resistant mutations are located between 28 and 37 min on the E. coli chromosome standard map, some distance from the rpoB gene at 89.5 min. The DNA-dependent RNA polymerase of these mutants is highly sensitive to rifampicin.