Impurities in commercial xanthine oxidase inhibit Ca pump and interfere in contractility of pig coronary artery

Commercial, but not pure, preparations of xanthine oxidase in the absence of an aldehyde or xanthine were observed to inhibit Ca-uptake by the subcellular membranes isolated from the smooth muscle of the pig coronary artery. This inhibition was not due to xanthine oxidase but a contaminant in the preparation. The commercial preparation caused a greater relaxation of the PGF2 alpha contracted coronary artery than the pure enzyme. The tissues treated with the commercial xanthine oxidase partially lost the ability to contract subsequently to PGF2 alpha.     

Uptake and release of calcium by canine gastric corpus smooth muscle plasma membrane enriched fraction

Calcium movements across plasma membrane enriched vesicles isolated from canine gastric corpus smooth muscle were investigated. The ATP-dependent Ca2+ uptake increased with time up to 10 min. The uptake for the initial 2-min period was approximately linear with time. The apparent initial velocity of the ATP-dependent Ca2+ uptake increased monotonically with free Ca2+ concentration from 0.1 to 2 microM, and further increases in free Ca2+ concentration did not increase the Ca2+ uptake. The free Ca2+ dependence curve could be described with a Hill coefficient of approximately 1.0 and Km of 0.85 +/- 0.01 microM for free Ca2+ concentration. Passive Ca2+ uptake (reaction time = 1 h) also increased with increasing free Ca2+ concentrations from 0.02 to 4.0 mM. Dilution of loaded vesicles in isotonic media containing EGTA led to initial rapid loss (less than 1 min) followed by a slower release which showed simple exponential decay. The t 1/2 values of the slower Ca2+ loss from these vesicles were 16.1 +/- 0.9 min (actively loaded n = 5) and 18.4 +/- 0.9 min (passively loaded n = 3), respectively. Dilution in isotonic medium containing both EGTA and A23187 released all the sequestered Ca2+ from these loaded vesicles.     

Body water metabolism in high altitude natives during and after a stay at sea level

Body fluid compartments were studied in a group of high altitude natives after a stay of two months at sea level and during 12 days at an altitude of 3,500 m. Measurements of total body water and extracellular water were made on day 3 and 12 of reinduction to altitude, while plasma volume was measured on day 12 only. The intracellular water, blood volume and red cell mass were computed from the above parameters. Total body water and intracellular water decreased by 3.3% (P<0.001) and 5.0% (P<0.001) respectively by the 3rd day at altitude and did not change thereafter. Extracellular water increased progressively at altitude, but the increase was not significant. Blood volume and red cell mass increased significantly while plasma volume decreased at altitude. These data were compared with that of low landers. This study suggested body hypohydration on high altitude induction in low landers as well as in high altitude natives on reinduction.     

The metabolic activation of 7-methylbenz(a)anthracene in mouse skin

The metabolism of 7-methylbenz(a)anthracene by rat-liver preparations and by mouse skin has been studied using a combination of thin-layer and high pressure liquid chromatography and all five possible trans-dihydrodiols have been detected as metabolites but in different proportions. The roles of these dihydrodiols and of the related vicinal diol-epoxides in the metabolic activation of 7-methylbenz(a)anthracene in mouse skin has been studied using Sephadex LH-20 column chromatography. The results show that the hydrocarbon-nucleic acid products formed in mouse skin in vivo most probably arise from 3,4-dihydro-3,4-dihydroxy-7-methylbenz(a)anthracene 1,2-oxide which, on the basis of this and other evidence, appears to be the reactive intermediate involved in the metabolic activation of 7-methylbenz(a)anthracene in this tissue.     

Effect of disulphonic stilbenes on Ca2+ transport in smooth muscle plasma membranes

We studied the effects of two disulphonic stilbenes, 4',4'-diisothiocyano-2,2'-stilbene disulphonic acid (DIDS) and 4-acetamido-4'-isothiocyano-2,2'-stilbene disulphonic acid (SITS), on Ca2+ transport by plasma membrane vesicles from the circular muscle of the dog stomach. Both compounds inhibited ATP-dependent Ca2+ uptake and reduce the leak from loaded vesicles. The inhibition produced could not be significantly reduced by either permeant anions or by increasing the level of free Ca2+. The effects of DIDS could be rendered irreversible by incubating the membranes with this agent at 37 degrees C.