KCa channel antagonists reduce NO donor-mediated relaxation of vascular and tracheal smooth muscle.

Electrophysiological studies suggest that activation of large-conductance Ca-activated K channels (KCa) with nitric oxide (NO) causes hyperpolarization and relaxation of smooth muscle. We determined whether KCa blockers decreased relaxation to the NO donors S-nitroso-N-acetylpenicillamine (SNAP) and 3-morpholinosydonimine-hydrochloride (SIN-1) in isolated segments from main pulmonary artery (MPA), its left branch (LPA), aorta (Ao), carotid artery (CA), and trachea (Tr). NO donors caused concentration-dependent relaxation of tissues precontracted with histamine whereas the inactive carrier molecule C88-3934 was without effect. The rank order profiles of SNAP and SIN-1 sensitivity were CA = Ao = MPA > LPA = Tr. Compared with histamine, 80 mM KCl precontraction caused variable reductions in tissue sensitivity and maximum relaxation to SNAP. The KCa antagonists charybdotoxin, iberiotoxin, and tetraethylammonium decreased sensitivity to SNAP and SIN-1 2- to 11-fold in MPA, LPA, and Tr, with variable shifts in Ao and CA. The effect of iberiotoxin was not altered by removing the endothelium or epithelium. Furthermore, charybdotoxin or iberiotoxin did not alter basal or SNAP-stimulated guanosine 3',5'-cyclic monophosphate content. Glibenclamide, noxiustoxin, and leiurotoxin I, antagonists of ATP-dependent, delayed rectifier, and small-conductance KCa channels, respectively, had no effect. In conclusion, antagonists of KCa decrease NO donor-mediated relaxation of pulmonary arterial and tracheal smooth muscle.

Differential blockade by tachykinin NK1 and NK2 receptor antagonists of bronchoconstriction induced by direct-acting agonists and the indirect-acting mimetics capsaicin, serotonin and 2-methyl-serotonin in the anesthetized guinea pig.

This study has examined the abilities of (+/-)-CP96345 and (+/-)-SR48968, nonpeptide antagonists selective for the tachykinin NK1 and NK2 receptors, respectively, to block bronchoconstriction caused by intravenous administration of direct-acting receptor agonists and the indirect-acting mimetics capsaicin, serotonin and 2-methyl-serotonin in the anesthetized guinea pig. The NK1 antagonist (+/-)-CP96345 was found to cause, at a maximally tolerated dose of 9 mumol/kg, an approximate 10-fold rightward shift of the dose-response curves for selective NK1 agonists substance P (SP), [Sar9,Met(O2)11]SP and Ac-[Arg6,Sar9,Met(O2)11]SP6-11 without altering responses to selective NK2 agonists neurokinin A (NKA), [Nle10]NKA4-10 or [beta-Ala8]NKA4-10. The NK2 antagonist (+/-)-SR48968 caused dose-dependent rightward shifts of the dose-response curves for the NK2 but not the NK1 agonists. Results using combinations of the receptor antagonists indicate that the NK2 agonists could cause bronchoconstriction by acting on the NK1 receptors at large doses relative to those used without antagonists. Of the agonists used here, [beta-Ala8]NKA4-10 appeared to be the most selective for the NK2 receptors. When used alone, only (+/-)-SR48968 was found to block bronchoconstriction caused by capsaicin, serotonin (after blockade of 5-HT2 receptors by LY53857) and 2-methyl-serotonin. When (+/-)-CP96345 was also given, larger additional blockade was seen with capsaicin than with serotonin or 2-methyl-serotonin as mimetic substance. Atropine caused small and variable degrees of blockade of serotonin and 2-methyl-serotonin but not of capsaicin after combinations of the two antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of experimentally induced nephrosis on protein synthesis in rat liver.

A nephrotic syndrome was experimentally induced in rats by a single intravenous injection of aminonucleoside of puromycin. Experimental animals were studied 8 days after the injection, at which time they exhibited marked proteinuria and hypoalbuminemia compared with control animals. The experimental animals also exhibited alterations in protein synthesis in liver as evidenced by a marked increase in the rate of albumin synthesis relative to total hepatic protein synthesis, changes in the relative concentrations of several plasma proteins, an increased protein content of plasma, an increased liver weight relative to body weight, and an increased RNA content of liver. Perfused liver preparations derived from nephrotic rats exhibited an increased release of albumin and other secretory proteins compared with control preparations. In contrast, there was no difference in the rate of synthesis of nonexported proteins between the two groups. The elevation in the relative rate of albumin synthesis was accompanied by a relative increase of the same magnitude in albumin mRNA. Furthermore, the relative amounts of several other mRNAs, including those coding for beta-fibrinogen, haptoglobin, metallothionein II, and two unidentified proteins, were increased, whereas the amount of mRNA coding for alpha 1-acid glycoprotein was decreased in livers of nephrotic rats compared to controls. These results indicate that nephrosis leads to marked alterations in the synthesis of albumin and other plasma proteins. Mechanisms responsible for these alterations include changes in the relative abundance of specific mRNAs and an increase in total cellular RNA.

Regulation of albumin synthesis by hormones and amino acids in primary cultures of rat hepatocytes.

Culture conditions necessary for optimizing albumin secretion were studied in rat hepatocytes maintained in a chemically defined, serum-free medium. Amino acid analysis of the culture medium, which was based on a 1:1 mixture of Ham's F12:Dulbecco's modified Eagle's medium (unsupplemented medium), revealed that certain essential amino acids were depleted from this medium over a 24-h incubation. Rates of albumin secretion were significantly higher and better maintained when the medium was supplemented with additional amino acids (supplemented medium). Moreover, selective removal of an essential amino acid resulted in an immediate decrease in total protein and albumin synthesis and after 48 h a further selective decrease in albumin synthesis. Linear rates of albumin secretion were observed over a wide variety of experimental conditions, but secretion was not strictly proportional to cell number. Maximal rates of secretion were obtained at plating densities of 2-3 X 10(6) cells/60 mm culture dish. Albumin secretion also increased with time in culture reaching a maximum on days 3 and 4. When added singly, either insulin or dexamethasone increased rates of albumin secretion in a dose-dependent manner, but both hormones and an adequate supply of amino acids were necessary for maximal rates of secretion as well as long-term maintenance of the hepatocytes (greater than 3-4 days). In the presence of dexamethasone the dose-response curve for insulin was shifted toward physiological insulin concentrations. Changes in rates of albumin secretion in response to added hormones in supplemented media were found to parallel changes in albumin synthesis and relative amounts of albumin mRNA. Changes in gene transcription were probably involved.