Single chloride-permeable channels of large conductance in cultured cardiac cells of new-born rats

Large conductance channels were observed in the membrane of cultured cardiac cells of newborn rats studied with the patch-clamp technique in cell-attached and inside-out configurations. These channels were observed in 4% of the patches. In the cell-attached configuration they exhibited outward rectification and partial inactivation. In the inside-out configuration no rectification occurred but inactivation was present, mainly during hyperpolarizations. Two channels with large single unit conductances (400–450 pS) and one with a smaller conductance (200–250 pS) were frequently observed in the same patch. The two large channels generally had different kinetics. Under steady-state conditions the opening probability of the faster channel appeared to be voltage-independent. The slower channel was activated by depolarization. In asymmetrical solutions the permeability ratios P _Na/P _Cl were 0.03 and 0.24 for the larger and smaller channels, respectively; corresponding values for P _Ba/P _Cl were 0.04 and 0.09. It is proposed that in cardiac membranes the chloride permeability system is composed of widely dispersed microclusters forming grouped channels of different types and sizes.     

Thermoregulatory responses of the immature rat following repeated postnatal exposures to 2,450-MHz microwaves

This study was designed to determine the changes that occur in the thermoregulatory ability of the immature rat repeatedly exposed to low-level microwave radiation. Beginning at 6-7 days of age, previously untreated rats were exposed to 2,450-MHz continuous-wave microwaves at a power density of 5 mW/cm2 for 10 days (4 h/day). Microwave and sham (control) exposures were conducted at ambient temperatures (Ta) which represent different levels of cold stress for the immature rat (ie, "exposure" Ta = 20 and 30 degrees C). Physiological tests were conducted at 5-6 and 16-17 days of age, in the absence of microwaves, to determine pre- and postexposure responses, respectively. Measurements of metabolic rate, colonic temperature, and tail skin temperature were made at "test" Ta = 25.0, 30.0, 32.5, and 35.0 degrees C. Mean growth rates were lower for rats exposed to Ta = 20 degrees C than for those exposed to Ta = 30 degrees C, but microwave exposure exerted no effect at either exposure Ta. Metabolic rates and body temperatures of all exposure groups were similar to values for untreated animals at test Ta of 32.5 degrees C and 35.0 degrees C. Colonic temperatures of rats repeatedly exposed to sham or microwave conditions at exposure Ta = 20 degrees C or to sham conditions at exposure Ta = 30 degrees C were approximately 1 degrees C below the level for untreated animals at test Ta of 25.0 degrees C and 30.0 degrees C. However, when the exposure Ta was warmer, rats exhibited a higher colonic temperature at these cold test Ta, indicating that the effectiveness of low-level microwave treatment to alter thermoregulatory responses depends on the magnitude of the cold stress.     

Phenobarbital and 6-aminonicotinamide effect on cerebral enzymatic activities related to energy metabolism in different rat brain areas

The effect of phenobarbital (100 mg/kg i.p.) and 6-aminonicotinamide (6AN) (35 mg/kg i.p.) on enzyme activities related to energy transduction was investigated on the homogenate in toto, non-synaptic mitochondrial fraction and synaptosomal fraction isolated from different rat brain areas (cerebral cortex, hippocampus, hypothalamus, striatum, and medulla oblongata). 6AN treatment decreased: (a) phosphofructokinase in all the areas tested; (b) lactate dehydrogenase on the homogenate in toto in striatum and hypothalamus, and on the synaptosomal fraction in cerebral cortex and corpus striatum; (c) succinate dehydrogenase on non-synaptic mitochondrial fraction in hippocampus and striatum. Finally, aspartate aminotransferase was increased on non-synaptic mitochondrial fraction in striatum and medulla oblongata. Phenobarbital treatment induced an increase of total NADH cytochrome c reductase on mitochondrial fraction in hippocampus and hypothalamus, and a decrease of cytochrome oxidase activity on non-synaptic mitochondrial fraction in hypothalamus and medulla oblongata.     

Role of phospholipases in myocardial ischemia: effect of cardioprotective agents on the phospholipases A of heart cytosol and sarcoplasmic reticulum in vitro

Increased breakdown of myocardial phospholipids to fatty acids and lysophosphoglycerides is an early feature of myocardial ischemic injury and many investigators believe that enhanced phospholipase action is an important factor in the process. Several recent reports indicate that inhibitors of phospholipase A, such as mepacrine, chloroquine and chlorpromazine, can prevent heart phosphoglyceride breakdown in vivo. We isolated the phospholipases A from rat heart cytosol and sarcoplasmic reticulum and examined the effects of various cardioprotective substances on their activity. Most of the cardioprotective agents studied inhibited the heart phospholipases in vitro, providing further evidence that phospholipid degradation in ischemic myocardial injury may be modulated by pharmacologic agents.     

Modulation of asialoglycoprotein binding activity in livers of pregnant or estrogen-treated rats

This report deals with the modulation of activity and expression of the hepatic asialoglycoprotein receptor, in pregnant or diethylstilbestrol-treated rats.The results show a two-fold increase in the total cell associated binding activity, both in pregnant and in estrogen-treated animals, with respect to normal values. On the contrary the surface expression was shown to be strongly enhanced only in the liver of pregnant rat. Therefore the modulation shown by this receptor system in pregnancy seems to be only partially estrogen-dependent.     

Induction of hepatic metallothionein by salicylate in adult rats

Application of salicylate increased the concentration of metallothionein (MT) in liver of pregnant rats as well as of adult male rats, whereas in fetal liver, MT was reduced by salicylate. Induction of MT synthesis by salicylate is an indirect effect because in cultured hepatocytes salicylate did not induce MT synthesis. Salicylate increased MT also in adrenalectomized rats. Indomethacin induced the same concentration of MT in maternal liver as salicylate. However, indomethacin had no effect on MT in fetal liver. Induction of MT in adult liver by salicylate and indomethacin was independent of zinc.     

Effects of etretinate on the distribution of elements in rats

We studied in the rat the effects of the drug etretinate (Tigason), given at three doses 3, 10, and 30 mg/kg body wt for 1 mo, on the concentrations of Na, K, Ca, Mg, Fe, S, P, Cu, and Zn in the plasma, brain, thymus, heart, liver, lung, kidney, testicle, muscle, and bone. The elements were simultaneously determined in tissues after nitric acid dissolution by inductively coupled plasma emission spectrometry using a JY 48 instrument. At the dose of 3 mg/kg, etretinate did not induce any statistically significant modifications of the element distribution. At the dose of 10 mg/kg, the main observed modifications were in plasma an increase of copper (+38%) and a decrease of zinc (-25%). At the highest dose of 30 mg/kg, some variations of the concentrations of elements in tissues were observed. But, on no account did retinoids induce an alteration of the mineral composition of bone, despite obvious macroscopic bone alterations.     

On the mechanism of cellular cadmium uptake

Review of the available evidence on the mechanism of cellular Cd uptake in the rat jejunum supports the concept that this process consists of nonspecific binding to anionic sites on the membrane, followed by a temperature-dependent and rate-limiting internalization step. Because temperature-sensitive transmembrane movement of Cd can be demonstrated also in isolated brush-border vesicles and in erythrocyte ghosts, it is not likely to result from pinocytosis but may be related directly to membrane fluidity. There is no need to assume the existence of saturable Cd carriers, or competition of Cd with essential polyvalent cations for their specific transport systems. Uptake of Cd by tubular epithelium in the kidney of the intact rabbit appears to resemble that described for the jejunum, with the internalization step limiting the rate of uptake.     

Multielement analysis of biological samples by inductively coupled plasma-mass spectrometry

Interest in the biological behavior of a growing number of elements, along with increasing recognition of the importance of interactions among them, demands a versatile and reliable technique for multielement analysis of biological samples. Significant improvements over the sensitivity achieved with conventional inductively coupled plasma (ICP) optical emission spectrometries have been realized with the introduction of quadrupole mass spectrometry (MS) for detection of ions in the plasma. The hybrid technique of ICP-MS promises to be a method of rapid multielement analysis, at detection limits that approach or surpass those of other technologies. However, the application of ICP-MS to analyses of biological interest is truly in its infancy. Here we report the use of ICP-MS for the determination of more than 30 elements of biological interest in a tissue and a biological fluid (rat liver and serum, respectively). Experimental values of the elements serve as a basis for discussion of analytical protocols, performance criteria, and certain problems peculiar to ICP-MS.     

Insulin binding in the hypothalamus of lean and genetically obese Zucker rats

Recent reports have suggested that the obesity and hyperphagia of the genetically obese Zucker rat may be related to defective insulin action or binding in the hypothalamus. We used quantitative autoradiography to determine if insulin binding is altered in specific hypothalamic nuclei associated with food intake. Insulin binding was measured in the arcuate (ARC), dorsomedial (DMN), and ventromedial (VMN) hypothalamic nuclei of 3–4-month-old lean (Fa/Fa) and genetically obese (fa/fa) Zucker rats. A consistently reproducible 15% increase in the total specific binding of 0.1 nM [¹²⁵I]-insulin was found in the ARC of the obese genotype. A slight increase in insulin binding in the DMN was also found. No difference in specific insulin binding was found between genotypes in the VMN. Nonlinear least squares analysis of competitive binding studies showed that the K_d of the ARC insulin binding site was 33% higher in the lean rats than in the obese rats, indicating an increased affinity for insulin. No difference in site number (B_max) was found in the ARC, DMN or VMN, and no evidence was found for reduced insulin binding in the hypothalamus of the obese (fa/fa) genotype. The results suggest that hyperphagia and obesity of the obese (fa/fa) Zucker rat genotype may be associated with increased insulin binding in the arcuate nucleus.