Effects of caffeine, verapamil, lithium, and KB-R7943 on mechanics and energetics of rat myocardial bigeminies.

We examined the effects of pharmacological alteration of Ca2+ sources on mechanical and energetic properties of paired-pulse ("bigeminic") contractions. The fraction of heat release that is related to pressure development and pressure-independent heat release were measured during isovolumic contractions in arterially perfused rat ventricles. The heat released by regular and bigeminic contractions showed two brief pressure-independent components (H1 and H2) and a pressure-dependent component (H3).

Mechanical and energetic effects of chronic chagasic patients' antibodies on rat myocardium.

Chagasic (Ch) and nonchagasic (NCh) IgG fraction (20 microg/ml) effects on cardiac performance of adult Wistar rat ventricles were studied with a novel approach applying a microcalorimetric technique. Resting heat (Hr) was significantly decreased by Ch antibodies (DeltaHrCh = 4.8 +/- 0.

Lithium and KB-R7943 effects on mechanics and energetics of rat heart muscle.

The role of calcium influx on energy expenditure during cardiac contraction was studied. For this purpose, the described ability of lithium and KB-R 7943 (KBR) to diminish Ca entry through Na-Ca exchanger (Ponce-Hornos & Langer, J Mol Cell Cardiol 1980, 12, 1367, Satoh et al., Circulation 2000, 101, 1441) were used.

A comparison of no-flow and low-flow ischemia in the rat heart: an energetic study.

Heat production under no-flow ischemia (ISCH) and under hypoperfusion (HYP) conditions was measured in single isovolumetric contractions of perfused rat ventricles at 25 degrees C. Resting heat production (Hr) and resting pressure decreased when the perfusion rate was reduced from 6 to 1.5 mL min(-1) or lower flows (HYP) and by ISCH.

Energetics of Na(+)-Ca(2+) exchange in resting cardiac muscle.

The energetic effect of extracellular Na(+) removal and readmission (in a nominally Ca(2+)-free perfusate) in Langendorff-perfused ventricles of transgenic mice (TM), which overexpress the sarcolemmal Na(+)-Ca(2+) exchanger; normal mice (NM); young (7-12 days old) rats (YR); and older (13-20 days old) rats (OR) was studied. In all heart muscles, extracellular Na(+) removal induced an increase in heat production (H(1)). Na(+) readmission further increased heat production to a peak value (H(2)) followed by a decrease toward initial values.

The heart extrasystole: an energetic approach.

The consequences of an extrasystole (ES) on cardiac muscle's energetics and Ca2+ homeostasis were investigated in the beating heart. The fraction of heat release related to pressure development (pressure dependent) and pressure-independent heat release were measured during isovolumic contractions in arterially perfused rat ventricle. The heat release by a contraction showed two pressure-independent components (H1 and H2) of short evolution and a pressure-dependent component (H3).

Energetics of heart muscle contraction under high K perfusion: verapamil and Ca effects.

Tension-dependent (TDH) and tension-independent heat (TIH) release were measured during single isovolumetric contractions in the arterially perfused rat ventricle. Under perfusion with 7 mM K-0.5 mM Ca, TDH showed only one component (H3), whereas TIH could be divided into two components (H1 and H2) of short evolution (similar to the classically identified activation heat) and one component (H4) of long duration (dependent on mitochondrial respiration).

The energetics of the quiescent heart muscle: high potassium cardioplegic solution and the influence of calcium and hypoxia on the rat heart.

Heart basal metabolism has been classically studied as the energy expenditure of those processes unrelated to mechanical activity and often measured by rendering the heart inactive using cardioplegic solutions (usually by increasing extracellular K concentration ([Kle]). In arterially perfused rat heart (at 25 degrees C), raising [K]e from 7 to 25 mM at a constant extracellular Ca concentration ([Ca]e) (0.5 mM), induced an increase in resting heat production (Hr) from 4.

Tension-dependent and tension-independent energy components of heart contraction.

Heat production and isovolumetric pressure development (P) were measured simultaneously in the arterially perfused rat ventricle. The time course of the calorimetric signal that follows a contraction could be decomposed into four components of energy released. Three of these components (H1, H2, and H4) were pressure independent, only H3 correlated with either P or the pressure-time integral (PtI) (r > 0.

[Energetics of ionic behavior in heart muscle contraction. Physiologic and physiopathologic aspects].

It is widely accepted that the ionic movement across the different membrane systems (i.e. sarcolemma, sarcoplasmic reticulum, mitochondria), plays a major role on heart muscle metabolism.

Influence of extracellular potassium on energetics of resting heart muscle.

The effects of various extracellular K concentrations ([K]e) on energy expenditure and their relationship to ionic exchange mechanisms under quiescent conditions were investigated in the arterially perfused rat heart. The increase in [K]e (from 6 to 12, 24, or 50 mM K) leads to a rapid increase (results are given per gram dry weight) in resting energy expenditure (+5.9 +/- 0.

Caffeine effects on heart muscle energetics: species differences.

The effects of caffeine (1mM) on energy expenditure and mechanical parameters in rat and toad perfused heart ventricles were examined at various stimulation frequencies. While in rat muscles caffeine significantly depressed developed tension and maximal rates of contraction and relaxation at all frequencies tested, in toad ventricle a slight positive inotropic effect was observed. Even though caffeine did not alter total contraction time in both preparations, in the rat ventricle the last part of relaxation was prolonged.

Heat production in isolated heart myocytes: differences among species.

A new calorimetry method has been developed to measure heat production from heart cell suspensions under continuous perfusion. The method is technically independent of the temperature at which the measurements are made, allows full control of the perfusion media, and is suitable for various biological preparations such as cells from diverse tissues, membrane vesicles, or skinned cells. The resting heat rate (Hr) measured at 18.

Role of extracellular calcium on heart muscle energetics: effects of verapamil.

The mechanical and energetic effects of verapamil (VER) and reduction of extracellular Ca concentration ([Ca]o) were studied in the interventricular rabbit septa and the dog papillary muscle. Even though the negative inotropic effects of VER [i.e.

Effects of caffeine on energy output of rabbit heart muscle.

The effects of caffeine (1 mmol.l-1) on mechanical and energetic parameters in the arterially perfused interventricular rabbit septa were examined at various frequencies of stimulation. Even though 1 mmol-1 caffeine induced a negative inotropic effect only at stimulation rates higher than 0.

The role of extracellular sodium on heart muscle energetics.

A study has been made of changing external sodium concentration [Na]e, over the range 75 to 200 mmol X l-1, on contractile parameters and heat production in isolated, arterially perfused, interventricular rabbit septa.- The observed changes in maximum rate of contraction with [Na]e, either in the presence of a constant external Ca concentration [Ca]e or in the presence of a constant [Na]e2/[Ca]e ratio, paralleled those observed for tension development (T). On the other hand the maximal rate of relaxation (-Tmax) and the ratio -Tmax/T increased.

Calcium effects on contractility and heat production in mammalian myocardium.

The effects of changing external Ca concentration ([Ca]o) on contractile parameters and heat production were investigated in the interventricular rabbit septa and the dog papillary muscle. Double reciprocal plots of tension development as a function of [Ca]o yielded half-maximal activation values of 1.04 +/- 0.

Effects of papaverine on calcium efflux and contractility in superfused rat left atria.

The effects of papaverine upon force of contraction, maximal rate of contraction, maximal rate of relaxation and 45Ca efflux were studied in isolated superfused rat left atria electrically driven at 1 Hz. Papaverine (3 X 10(-5) mol/l, increased developed tension (from 5.35 +/- 1.

Sodium compartmentalization of the arterial wall revisited: ouabain, temperature and enzymatic effects.

The sodium (Na) fractions of the dog carotid artery were identified by analyzing the effects of different procedures on 24Na washout curves. Although these never yielded more than three exponential terms, four Na fractions were identified. The fast-exchanging component amounted to 73 mmoles Na/kg w.

Simultaneous analyses of Ca exchange and mechanical parameters in the rat atria.

In the rat left atrium, electrically driven, a superfusion dropping method was developed. The device essentially consisted of a pair of platinum wire electrodes which held one end of the tissue, while the other end was attached to an isometric tension transducer. Either normal or isotopically labeled solutions were poured on the preparation at preset flow rates by means of a minipump.

Energetic, metabolic and contractile effects of vasopressin in mammalian heart.

The effects of arginine vasopressin (VP), 8 mU/ml, on contractility, heat production and glucose metabolism were investigated in isolated, arterially perfused, interventricular rabbit septa. Rest tension linearly increased in the presence of VP with a slope of 0.095 +/- 0.

Role of extracellular volume expansion in the development of DOC-salt hypertension in the rat.

Changes in inulin space, plasma and blood volume, exchangeable and "noninulin" sodium were studied during the prehypertensive, early and late hypertensive stages of deoxycorticosterone (DOC)-salt administration in the rat. The effect of an acute water load in previously nephrectomized animals was also studied. Hypertension developed after 1 to 2 weeks of the DOC-salt regimen and was always preceded by enlargement of the inulin space and increased plasma and blood volume.

On-line calorimetry in the arterially perfused rabbit interventricular septum.

A method has been developed to measure myocardial heat production simultaneously with mechanical (developed tension, rate of contraction and relaxation) and metabolic parameters in the arterially perfused interventricular septum of the rabbit. The system allows control of rest tension, frequency of contraction, temperature, and composition of the perfusate. The technique is based on the differential measurement of the heat flux from the muscle to the calorimetric bath.

Effects of inorganic phosphate on ion exchange, energy state, and contraction in mammalian heart.

Effects of inorganic phosphate (Pi) on contractile function, ionic exchange, and cellular energetic state were investigated in isolated, arterially perfused, interventricular rabbit septa. The addition of 10 or 20 mM Pi to a N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) buffered perfusate showed 1) a decrease in developed tension due to a decrease in free Ca concentration; 2) an increase in diastolic tension; 3) a decrease in 42K uptake at the same time that 42K efflux was depressed; 4) an increase of 24Na activity; 5) an increase in tissue 47Ca activity; and 6) a decrease in tissue adenosine 5'-triphosphate (ATP) levels. If a 10-mM Pi intervention was applied without changing the free Ca concentration of the perfusate, the mechanical record showed a transient positive inotropic effect without changes in K efflux.