Relation between mitochondrial calcium transport and control of energy metabolism.

The effects of sodium pump inhibition produced by exposure to the cardiac glycosides, ouabain or dihydroouabain, or by reduction in extracellular potassium to 1.0 mM, on contractile state and sodium-calcium exchange were studied in primary monolayer cultures of chick embryo ventricular cells. Ouabain, 10(-6)M, dihydroouabain, 5 X 10(-5)M, and extracellular potassium of 1.0 mM all induced similar and prominent positive inotropic effects. These effects were accompanied, in each case, by 40-50% inhibition of the rate of active uptake of 42K and by similar increases in steady state sodium content. Stimulation of the rate of 45Ca uptake on exposure to zero extracellular sodium occurred in response to extracellular potassium (1.0 mM) or to glycoside concentrations that induced a positive inotropic effect and sodium-potassium pump inhibition. Reactivation of the sodium pump after return from 1.0 to 4.0 mM extracellular potassium was rapid and was associated with membrane hyperpolarization and slowing of spontaneous beating rate. With pump reactivation under these circumstances, the time course of disappearance of stimulation of sodium-calcium exchange on exposure to zero extracellular sodium was similar to the time course of loss of the positive inotropic effect. Under physiological conditions (4.0 mM extracellular potassium), exposure to positively inotropic but nontoxic concentrations of ouabain or dihydroouabain caused a small but consistent increase in unidirectional calcium influx, but had no discernible effect on calcium efflux. Since similar inotropic effects were produced for comparable degrees of glycoside or low extracellular potassium-induced sodium pump inhibition and increases in cellular sodium content, sodium pump inhibition rather than a glycoside-specific change in calcium binding appears to underlie the inotropic response. These findings are further consistent with the view that the primary mechanism of the positive inotropic effects of digitalis and low extracellular potassium in this experimental preparation is sodium pump inhibition resulting in increased intracellular sodium. We suggest that increased calcium influx via sodium-calcium exchange is the principal mechanism whereby increased intracellular sodium results in enhanced calcium availability to the myofibrils, but an additional effect on calcium efflux is not excluded.

Sodium pump inhibition, enhanced calcium influx via sodium-calcium exchange, and positive inotropic response in cultured heart cells.

• Myocardial depression is a major but poorly understood component of septic shock. This study investigates the morphologic and biochemical abnormalities associated with septic shock. Myocardial cells are incubated in normal and septic plasma in a nutrient-, oxygen-, pH-, electrolyte-, and temperature-controlled environment. Cells and media are tested for basal- and epinephrine-stimulated cyclic adenosine monophosphate (cAMP), lactic dehydrogenase (LDH), and creatine kinase. Electron microscopic studies are done at the end of incubation. Septic LDH and creatine kinase levels in the media are increased substantially, and septic cAMP levels are reduced significantly. Septic cells beat irregularly and arrest along with exhibiting abnormal electron microscopic structure. Septic myocardial dysfunction occurs independently of previously postulated causes that are controlled for in this experiment and therefore may be due to endogenously produced or accumulated toxic factor(s). (Arch Surg1985;120:30-35)

Myocardial Dysfunction in Septic Shock

Our studiesin vitro demonstrate that neutrophil mediated injury of isolated cardiac myocytes requires the presence of ICAM-1 on the surface of the myocyte and CD11b/CD18 activation on the neutrophil. In post-ischemic cardiac lymph, there is rapid appearance of C5a activity during the first hours of reperfusion. Interleukin-6 activity is present throughout the first 72 h of reperfusion and is sufficient to induce ICAM-1 on the surface of the cardiac myocyte.In situ hybridization studies suggest that ICAM-1 mRNA is found in viable myocardial cells on the edge of the myocardial infarction within 1 h of reperfusion. ICAM-1 protein expression on cardiac myocytes is seen after 6 h of reperfusion, and increases thereafter. Non-ischemic tissue demonstrates no early induction of ICAM-1 mRNA or ICAM-1 protein on myocardial cells. In our most recent experiments, we have determined that reperfusion is an absolute requirement for the early induction of myocardial ICAM-1 mRNA in previously ischemic myocardial cells. To further assess this, we have cloned and sequenced a canine interleukin-6 (IL-6) cDNA. The data suggest that early induction of IL-6 mRNA is also reperfusion dependent as it could be demonstrated in the same ischemic and reperfused segments in which ICAM-1 mRNA was found. Peak expression of IL-6 mRNA occurred much earlier than that for ICAM-1 mRNA. Similar experiments were then performed with a molecular probe for interleukin-8 (IL-8). This chemokine is a potent neutrophil stimulant and has a higher degree of specificity for neutrophils than classic chemoattractants such as C5a. The results suggest a similar pattern of induction that occurs within the first hour and is markedly, increased by reperfusion. The relationship of reperfusion to ICAM-1 and cytokine induction is discussed.

Role of early reperfusion in the induction of adhesion molecules and cytokines in previously ischemic myocardium

Role of the fast-exchanging calcium compartment in the early cardiotoxicity of anthracycline analogs

Evidence that concentrations of ouabain which induce positive inotropic effects on the perfused guinea-pig heart increase the amount of calcium in a rapidly-exchangeable cellular compartment.

The effects of adrenaline on kinetically-distinct compartments of exchangeable calcium in the spontaneously-beating perfused rat heart were investigated under steady-state conditions using a 45Ca2+ outflow technique together with a nonlinear least-squares curve fitting procedure and 51Cr-EDTA to monitor the loss of freely-diffusible Ca2+ from the extracellular space. In addition to Ca2+ distributed in the vascular (compartment 1) and interstitial (compartment 2) spaces, the minimum number of kinetically-distinct compartments of cellular exchangeable Ca2+ (which include Ca2+ bound to extracellular sites on the sarcolemma) required to fit the data (compartments 3,4 and 5) was three. A system in which cellular compartment 3 is linked to the vascular space and compartments 4 and 5 are linked to the interstitial space was consistent with the data. For hearts perfused under control conditions, the fractional transfer rates for Ca2+ outflow from cellular compartments 3, 4 and 5 were 0.70, 0.11 and 0.017 min−1, respectively. Adrenaline increased the quantity of exchangeable Ca2+ in compartment 5 and decreased that present in the compartment 4. Evidence that compartment 5 includes mitochondrial exchangeable Ca2+ is discussed. It is concluded that one of the actions of adrenaline on the heart is to increase the quantity of exchangeable Ca2+ in the mitochondria.

Effects of adrenaline on a compartment of slowly-exchangeable calcium in the perfused rat heart

Kinetic properties of exchangeable calcium in guinea-pig heart mitochondria measured at low concentrations of free calcium and in the presence of Mg2+, ATP4- and inorganic phosphate.

Suzanne V. Lamont

Papers

Evidence that concentrations of ouabain which induce positive inotropic effects on the perfused guinea-pig heart increase the amount of calcium in a rapidly-exchangeable cellular compartment.

Effects of adrenaline on a compartment of slowly-exchangeable calcium in the perfused rat heart

Kinetic properties of exchangeable calcium in guinea-pig heart mitochondria measured at low concentrations of free calcium and in the presence of Mg2+, ATP4- and inorganic phosphate.