Effect of perfusate ionized calcium on mechanical activity of the rat heart in deep hypothermia

Effects of different concentrations of ionized calcium ([Ca2+]) in perfusion fluid and of the heart temperature on the systolic pressure (Psyst), heart rate (Vc) and their product as general index of the heart mechanical activity (HMA) of the rat isovolumetrically contracting isolated heart preparations were examined in condition of retrograde perfusion at constant volume with a modified Krebs-Heseleit buffer. An increase of [Ca2+] from 0.62 to 2.5 mM (mmol/l) in the normothermia (38 degrees C) augments Psyst and HMA. Heart rate does not change. An increase of [Ca2+] from 0.62 to 4.5 mM at 20 degrees C augments Vc and HMA. An increase [Ca2+] at 15-11 degrees C decreases psyst and HMA. [Ca2+] does not affect the temperature of the heart arrest.     

Effect of potassium concentration and ouabain on the renal adaptation to potassium depletion in isolated perfused rat kidney

Renal adaptation for potassium (K) conservation has been demonstrated in isolated perfused kidneys from rats within 3 days of K depletion and appears to be independent of aldosterone and sodium excretion. This study was designed to investigate whether the renal adaptation for K conservation is independent of ambient [K] and renal tissue levels of K and whether ouabain may have effects on K excretion, which are in contrast to the effects on K excretion in normal animals. In the first study, rats K depleted for 3 days received 2500 mu equiv. KCI intraperitoneally, while other K-depleted rats and a group of control diet animals received intraperitoneal H2O alone to determine whether simple restoration of K deficits would reverse the renal adaptation for K conservation. Intraperitoneal KCI increased plasma [K] and kidney tissue K significantly within 3 h in the K-repleted group compared with the K-depleted rats. Isolated Kidneys were perfused from the three groups of rats 3 h after intraperitoneal injection. Despite K repletion in vivo, perfused kidneys from the K-repleted group still had significantly decreased K excretion (1.28 +/- 0.085 mu equiv./min) compared with controls (2.05 +/- 0.291 mu equiv./min), and K excretion was still not different from the K-depleted group (0.57 +/- 0.134 mu equiv./min). However, fractional K excretion by the kidneys from K-repleted rats was increased above K-depleted kidneys (0.48 +/- 0.051 vs. 0.18 +/- 0.034, p less than 0.01). Despite the increased renal tissue K in K-repleted kidneys at the start of perfusion (285 +/- 5.1 vs. 257 +/- 5.4 mu equiv./g), by the end of the perfusion tissue K in perfused kidneys was identical in all three groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impact of lactate in the perfusate on function and metabolic parameters of isolated working rat heart

The goal of this study was to investigate the effect of 1 mM exogenous lactate on cardiac function, and some metabolic parameters, such as glycolysis, glucose oxidation, lactate oxidation, and fatty acid oxidation, in isolated working rat hearts. Hearts from male Sprague-Dawley rats were isolated and perfused with 5 mM glucose, 1.2 mM palmitate, and 100 μU/ml insulin with or without 1 mM lactate. The rates of glycolysis, glucose, lactate, and fatty acid oxidation were determined by supplementing the buffer with radiolabeled substrates. Cardiac function was similar between lactate+ and lactate− hearts. Glycolysis was not affected by 1 mM lactate. The addition of lactate did not alter glucose oxidation rates. Interestingly, palmitate oxidation rates almost doubled when 1 mM lactate was present in the perfusate. This study suggests that subst rate supply to the heart is crucially important when evaluating the data from metabolic studies.     

Effect of perfusate pH on coronary flow and adenosine release in isolated rabbit heart

This study was undertaken in an attempt to further understand the relationship between adenosine and H+ ion. Using Langendorff hearts from male rabbits, the perfusion fluid pH was lowered from 7.4 to 7.1 and 6.8 with CO2. A 31 and 86% increase in coronary flow with a simultaneous increase in the release of adenosine by 61 and 128% was observed at pH 7.1 and 6.8, respectively. A direct relationship between adenosine release and coronary flow with a correlation coefficient of 0.99 was found at pH values of 7.4, 7.1, and 6.8. The degradation products of adenosine namely inosine and hypoxanthine were unchanged at 7.1 and 6.8 from 7.4. These data support a role for adenosine in the regulation of coronary flow and suggest a relationship between adenosine and H+ ion.     

Effect of acute hypothermia on parameters of tetanic contraction of the rat skeletal muscle

In rats under acute hypothermia, tetanic tension of the medial m. gastrocnemius had a higher amplitude.     

Determination of the rate of K movement through potassium channels in isolated rat heart and liver mitochondria

Both ATP-regulated (mitoK_ATP) and large conductance calcium-activated (mitoBK_Ca) potassium channels have been proposed to regulate mitochondrial K⁺ influx and matrix volume and to mediate cardiac ischaemic preconditioning (IP). However, the specificity of the pharmacological agents used in these studies and the mechanisms underlying their effects on IP remain controversial. Here we used increasing concentrations of K⁺-ionophore (valinomycin) to stimulate respiration by rat liver and heart mitochondria in the presence of the K⁺/H⁺ exchanger nigericin. This allowed rates of valinomycin-induced K⁺ influx to be determined whilst parallel measurements of light scattering (A₅₂₀) and matrix volume (³H₂O and [¹⁴C]-sucrose) enabled rates of K⁺ influx to be correlated with increases in matrix volume. Light scattering readily detected an increase in K⁺ influx of < 5 nmol K⁺ min^− 1 per mg protein corresponding to < 2% mitochondrial matrix volume increase. In agreement with earlier data no light-scattering changes were observed in response to any mitoK_ATP channel openers or blockers. However, the mitoBK_Ca opener NS1619 (10-50 µM) did decrease light scattering slightly, but this was also seen in K⁺-free medium and was accompanied by uncoupling. Contrary to prediction, the mitoBK_Ca blocker paxilline (10-50 µM) decreased rather than increased light scattering, and it also slightly uncoupled respiration. Our data argue against the presence of significant activities of either the mitoK_ATP or the mitoBK_Ca channel in rat liver and heart mitochondria and provide further evidence that preconditioning induced by pharmacological openers of these channels is more likely to involve alternative mechanisms.     

Determination of the rate of K(+) movement through potassium channels in isolated rat heart and liver mitochondria

Both ATP-regulated (mitoK(ATP)) and large conductance calcium-activated (mitoBK(Ca)) potassium channels have been proposed to regulate mitochondrial K(+) influx and matrix volume and to mediate cardiac ischaemic preconditioning (IP). However, the specificity of the pharmacological agents used in these studies and the mechanisms underlying their effects on IP remain controversial. Here we used increasing concentrations of K(+)-ionophore (valinomycin) to stimulate respiration by rat liver and heart mitochondria in the presence of the K(+)/H(+) exchanger nigericin. This allowed rates of valinomycin-induced K(+) influx to be determined whilst parallel measurements of light scattering (A(520)) and matrix volume ((3)H(2)O and [(14)C]-sucrose) enabled rates of K(+) influx to be correlated with increases in matrix volume. Light scattering readily detected an increase in K(+) influx of <5 nmol K(+) min(-1) per mg protein corresponding to <2% mitochondrial matrix volume increase. In agreement with earlier data no light-scattering changes were observed in response to any mitoK(ATP) channel openers or blockers. However, the mitoBK(Ca) opener NS1619 (10-50 microM) did decrease light scattering slightly, but this was also seen in K(+)-free medium and was accompanied by uncoupling. Contrary to prediction, the mitoBK(Ca) blocker paxilline (10-50 microM) decreased rather than increased light scattering, and it also slightly uncoupled respiration. Our data argue against the presence of significant activities of either the mitoK(ATP) or the mitoBK(Ca) channel in rat liver and heart mitochondria and provide further evidence that preconditioning induced by pharmacological openers of these channels is more likely to involve alternative mechanisms.     

Determination of intracellular potassium ion concentration in isolated rat ventricular myocytes

The sarcoplasmic potassium concentration of a suspension of rat ventricular myocytes, prepared by collagenase-induced disruption of the myocardial mass, was determined by a null-point technique. Addition of digitonin resulted in a release of potassium from the cells which was interpreted as a flux from the sarcoplasm. The intracellular potassium concentration was estimated to be 113 +/- 6mM.     

Effect of glucose on potassium contracture tension in rat heart

The effect of substrates on potassium contracture tension of the isolated rat ventricle strip was investigated. The contracture tension magnitude of ventricle strips exposed to potassium rich medium was markedly greater with medium containing pyruvate or acetate than with glucose as the substrate. The effect of substrates on contracture tension was not related to their ability to maintain the ATP stores of the heart, for there was not a significant difference in the ATP levels in ventricle strips incubated in medium containing pyruvate, pyruvate + glucose, or glucose. Glucose reduced the K-contracture tension magnitude of heart strips suspended in medium containing pyruvate or acetate as substrate; 3-0-methylglucose and 2-deoxy-D-glucose did not have this action on K-contracture tension. The reduction of K-contracture tension by glucose was inhibited by iodoacetate and fluoride. Under anaerobic conditions, 50 mM glucose significantly reduced the K-contracture tension of ventricle strips suspended in pyruvate medium. The findings of this study suggest that glucose metabolism has an action on K-contracture tension in cardiac muscle that is not shared by acetate or pyruvate.