Ca2+-independent inhibition of myocardial contraction by coronary effluent of hypoxic rat hearts

Human adipocytes attenuate cardiomyocyte contraction: characterization of an adipocyte-derived negative inotropic activity

The causal relationship between obesity and heart failure is broadly acknowledged; however, the pathophysiological mechanisms involved remain unclear. In this study we investigated whether human adipocytes secrete cardioactive substances that may affect cardiomyocyte contractility. We cultivated adipocytes obtained from human white adipose tissue and incubated isolated rat adult cardiomyocytes with adipocyte-conditioned or control medium. This is the first report to demonstrate that human adipocytes exhibit cardiodepressant activity with a direct and acute effect on cardiomyocyte contraction. This adipocyte-derived negative inotropic activity directly depresses shortening amplitude as well as intracellular systolic peak Ca2+ in cardiomyocytes within a few minutes. The adipocyte-derived cardiodepressant activity was dose-dependent and was completely blunted by heating or by trypsin digestion. Filtration of adipocyte-conditioned medium based on molecular mass characterized the cardiodepressant activity at between 10 and 30 kDa. In summary, adipose tissue exerts highly potent activity with an acute depressant effect directly on cardiomyocytes, which may well contribute to increased heart failure risk in overweight patients.

Phenotypic properties and characteristics of superoxide production by mouse coronary microvascular endothelial cells

Coronary microvascular endothelial cells exert (patho)physiological effects on the function of cardiac myocytes, which may be studied experimentally using pure cell populations. As an essential pre-requisite to the investigation of cells from gene-modified mice, we studied the phenotypic properties of coronary microvascular endothelial cells isolated from normal mice, and biochemically characterized the superoxide production by these cells. Microvascular endothelial cells were isolated from devitalized mouse ventricular tissue after sequential digestion with collagenase, trypsin and DNase. Coronary microvascular endothelial cells were separated from cardiac myocytes and other cells by differential centrifugation, plating and culture. Mouse coronary microvascular endothelial cells showed an irregular "cobblestone" morphology at confluence, were >98% positive for CD31 by FACS analysis, and were also positive for VE-cadherin and endothelial-type nitric oxide synthase (eNOS) by confocal microscopy. The cells took up fluorescently labelled, acetylated low-density lipoprotein, but were negative for a alpha -smooth muscle actin, desmin and cytokeratin. Unlike human endothelial cells, mouse coronary microvascular endothelial cells only weakly expressed von Willebrand factor. Immunoblotting showed that the mouse cells expressed components of a phagocyte-type NADPH oxidase. They exhibited NADPH-dependent O(2)(-)-generating activity, which was increased by angiotensin II but completely inhibited by diphenyleneiodonium. Thus, mouse coronary microvascular endothelial cells express both eNOS and NADPH oxidase, interactions between which may play a role in endothelial cell pathophysiology.