In Vitro Work Load and Rat Heart Metabolism

The isolated working rat heart preparation was used to study the effects of well defined work loads on heart protein synthesis. The rate of protein synthesis was evaluated by measuring the incorporation rate of phenylalanine-³H into whole heart protein. Increased pressure load (afterload) accelerated the protein synthesis. A stimulatory effect was demonstrated with glucose or palmitate as substrate and with 1 or 5 times the normal rat plasma levels of all amino acids in the perfusion medium. The protein synthesis of both control and overloaded hearts was significantly accelerated with palmitate as substrate or with high levels of all amino acids. The work load effect could, thus, be obtained under conditions optimal for heart protein synthesis in vitro. In contrast to the stimulatory effect of in-creased afterload the rate of protein synthesis was not changed when the left atrial filling pressure (preload) was increased, although the external heart work was raised several times. End systolic volume was markedly increased in pressure overloaded hearts compared to hearts perfused under control conditions or with increased preload. It is concluded that an increase in contractile tension during systole and/or an increase in the end systolic volume was a necessary requirement for the acceleration of protein synthesis.     

In Vitro Work Load and Rat Heart Metabolism: III. Effect on ribosomal aggregation

In two preceding papers increased pressure load (afterload) was found to accelerate whole heart protein synthesis and amino acid transport in the perfused working rat heart (Hjalmarson and Isaksson 1972, Ahren et at. 1972). To further analyse this effect, sucrose gradient analysis of the postmitochondrial supernatant was performed to evaluate reactions involved in the ribosome cycle. When hearts were perfused in vitro under control conditions with buffer containing normal plasma levels of amino acids and with glucose as substrate, levels of polysomes decreased and levels of ribosomal subunits increased. These findings together with a decreased rate of protein synthesis indicated that a block in initiation of peptide chains had developed during perfusion. Perfusion of hearts with increased afterload increased the levels of polysomes and decreased the levels of ribosomal subunits and accelerated protein synthesis. The effects were obtained both when glucose and palmitate were used as substrate. Insulin further increased the levels of polysomes in pressure overloaded hearts and the ribosome profiles attained by overload in presence of insulin were identical to those obtained from unperfused hearts. Increased levels of polysomes and decreased levels of ribosomal subunits together with an increase in protein synthesis suggested that pressure overload stimulated reactions involved in the initiation of polypeptide chains. It is concluded that increased pressure load increases levels of initiation factors or changes the activity of enzymes regulating initiation processes in the ribosome cycle.     

In Vitro Effect of Acetylcholine on Function of Sinoatrial Node in Rat Heart

Electrophysiological parameters of true pacemakers in the sinoatrial node of rat heart were recorded intracellularly using glass microelectrodes. In 11 of 13 experiments acetylcholine in increasing doses did not induce migration of the dominant pacemaker region, while in two cases its minor migration upstream the sinus node artery was observed.     

Effect of Nicotine on Rat Gingival Fibroblasts In Vitro

Tobacco smoking is considered a major risk factor for the development and progression of periodontal diseases (Haber, J. and Wattles, J. (1994). J. Periodontol. 64, 16-23). The purpose of this study was to determine the effects of nicotine on rat gingival fibroblasts (RGF) cultured in vitro. After ether anesthesia, rat gingival tissues were obtained from the attached gingiva of a Wistar rat. Small fragments of gingiva were maintained in culture in Petri dishes. Fibroblasts developing from these explants were collected to obtain monolayer cultures. After the fourth passage (T4), cells were supplemented with nicotine at various concentrations. Control and treated cells were examined under phase contrast or transmission electron microscopy. They were compared as regards their DNA content, mitochondrial activity, collagen and protein synthesis, and cell death by apoptosis or necrosis. Nicotine from 0.05 uM to 1 miVl did not affect the DNA content or protein and collagen synthesis. At concentrations between 3 and 5 niM. growth was significantly diminished and the survival rate reduced. Ultrastructural analysis revealed dilated mitochondria and vacuolization in treated cells, suggestive of necrosis, but increased apoptosis was also revealed by cytometry. On the basis of this in vitro study, it appears that tobacco, through its component nicotine, may directly affect various functions of RGF.     

Metabolism of sulfur-containing amino acids in the dermatophyte Microsporum gypseum. II. Acidic amino acid derivatives

The dermatophyte Microsporum gypseum was cultivated on a glucose-arginine medium supplemented with five strongly acidic derivatives of cysteine (L-cysteine sulfinic acid, L-cysteic acid, L-serine-O-sulfate and taurine at a concentration of 5 mmol/l, and L-S-sulfocysteine at a concentration of 2.5 mmol/l). The addition of these substances did not stimulate the growth as compared with the control containing 0.5 mmol/l cystine. Cysteine sulfinic acid and cysteic acid showed rather inhibitory effects. A strong inhibition of the growth was caused by the presence of serine sulfate. During the growth, all substances investigated were gradually consumed and utilized not only as a source of sulfur but of nitrogen and carbon as well. Cysteine sulfinic acid and S-sulfocysteine were utilized most rapidly. Cysteic acid was also rapidly utilized but after a certain adaptation. Taurine was utilized slowly and serine sulfate very slowly. Excess sulfur contained in the substances used was excreted into the medium in the form of sulfate. Sulfate excretion was most rapid with cysteine sulfinic acid and slowest with taurine. With cysteine sulfinic acid, S-sulfocysteine and cysteic acid, small amounts of sulfite were found in the medium. The results obtained are in accordance with the presumption that cysteine sulfinic acid (but not cysteic acid and taurine) is an intermediate of cysteine catabolism in dermatophytes.     

Effect of amino acid meals on hepatic alpha-aminoisobutyrate transport and cyclic AMP.

Within 1.5 h after force-feeding rats one meal of enzymatic hydrolysates of casein, gelatin, lactalbumin, or yeast, alpha-aminoisobutyric acid (AIB) transport in liver slices was stimulated two- to threefold. A complete amino acid mixture also increased AIB transport. Of the 15 amino acids or derivatives tested individually, the dispensable amino acids, especially glycine and alanine, were more stimulatory than the essential amino acids; feeding a mixture of amino acids lacking glycine and alanine increased AIB uptake only slightly. The effects were significantly greater in meal-fed than in ad libitum-fed rats. Increased hepatic concentrations of cyclic AM were usually associated with the increase in AIB transport. Feeding glucose inhibited the increases in transport and cyclic AMP concentration induced by casein hydrolysate or in the stimulation of AIB transport by dietary amino acids. The increases in AIB uptake appeared unrelated to the exchange of endogenous amino acids with medium AIB.     

Effect of bile salts on amino acid transport by rabbit intestine.

The effect of bile salts on alanine absorption across four regional sites of rabbit intestine was examined using an in vivo single-pass perfusion technique. Na-deoxycholate at a concentration of 3 mM reduced alanine absorption across all levels of the intestine, and a higher concentration (10 mM) of Na-taurodeoxycholate (TDC) caused only a minimal reduction of alanine absorption in the jejunum. TDC, however, was more effective in in vitro experiments, causing an incrase in transmural serosal-to-mucosal flux of alanine and phenylalanine, particularly when present in both the mucosal and serosal media. It also reduced the mucosal-to-serosal alanine flux rate when present only in the mucosal medium. The influx of these amino acids across the mucosal brush border membrane was also decreased by TDC. These amino acid transport changes correlated fairly well with some observed histological changes of the intestinal epithelium. This suggests that bile salt inhibition of amino acid absorption is nonspecific in type and can be mainly explained as being the result of an injurious action of these surface-active agents on the rabbit intestine.     

Effect of Calcium on Embryonic Rat Thyroid C Cells In Vitro

The alterations in the ultrastructure of rat embryonic thyroid C cells in vitro produced by variation in the ambient calcium of the medium were studied. The thyroid C cells from 19-day-old rat fetuses were cultured for 48 hours in calcium concentrations of 2, 4, 6, 8 and 10 mg%. The C cells show a cyclic change in the ultrastructure. The resting cells have a sparse, dispersed granular endoplasmic reticulum, small Golgi apparatus and numerous secretory granules. The granules are emptied into the extracellular space followed by aggregation of the granular endoplasmic reticulum, enlargement of the Golgi apparatus, and reaccumulation of secretory products in granules. Varying the calcium concentration failed to change the proportion of cells in the various stages of the secretory cycle, though the mean number of secretory granules per unit area of cytoplasm fell proportionally with increasing ambient calcium concentration (y = -0.1675x +3.93). This decrease is largely due to a reduction in the number of cells with higher densities of secretory granules and corresponds to the direct increase in calcitonin content of the medium. This could indicate that secretion is directly stimulated in cells rich in secretory granules by a high calcium concentration. In contrast, these ultrastructural studies also indicate that, unlike the situation in the parathyroid chief cell, alteration of the ambient calcium concentration has little effect on the rate of synthesis of thyrocalcitonin by thyroid C cells.     

Effect of Dapagliflozin on the Functioning of Rat Liver Mitochondria In Vitro

Bulletin of Experimental Biology and Medicine - We studied the effect of a new hypoglycemic compound dapagliflozin on the functioning of rat liver mitochondria. Dapagliflozin in concentrations of...     

Effect of Lycopine on the Resistance of Rat Liver Microsomes to In Vitro Induced LPO

Lycopine in concentrations of 0.5-50 M suppressed LPO in microsomes induced by NADPH-Fe²⁺ and by ascorbic acid-Fe²⁺. Lycopine in a concentration of 20 M completely prevented the decrease in the rate of benz[a]pyrene hydroxylation and activation of p-nitrophenyl-UDP-glucuronosyl transferase caused by LPO induction in microsomes.     

Puromycin effect on amino acid transport: differential rates of carrier protein turnover.

In fetal rat calvaria, puromycin selectively inhibited the uptake of certain groups of amino acids. Puromycin treatment decreased the uptake of glycine, L-proline, and alpha-aminoisobutyric acid but was without effect on the active uptake of all other amino acids tested. In studies of alpha-aminoisobutyric acid uptake, puromycin decreased the maximal transport velocity by 70% but had no effect on the affinity of the transport system for the amino acid. With puromycin treatment, the fall-off in rates of alpha-aminoisobutyric acid uptake was first order with a half-life of 68 min. Insulin treatment increased this half-life to 118 min. These findings suggest that protein components of specific transport systems are degraded at varying rates after puromycin blockade of protein synthesis. Hormones that stimulate amino acid transport (e.g., insulin) may decrease the rate of degradation of these protein components.