Cardiomyocyte dysfunction during the chronic phase of Chagas disease.

Chagas disease, which is caused by the parasite Trypanosoma cruzi, is an important cause of heart failure. We investigated modifications in the cellular electrophysiological and calcium-handling characteristics of an infected mouse heart during the chronic phase of the disease. The patch-clamp technique was used to record action potentials (APs) and L-type Ca2+ and transient outward K+ currents. [Ca2+]i changes were determined using confocal microscopy. Infected ventricular cells showed prolonged APs, reduced transient outward K+ and L-type Ca2+ currents and reduced Ca2+ release from the sarcoplasmic reticulum. Thus, the chronic phase of Chagas disease is characterised by cardiomyocyte dysfunction, which could lead to heart failure.

Changes in cellular contractility and cytokines profile during Trypanosoma cruzi infection in mice.

Trypanosoma cruzi, an intracellular protozoan parasite infecting a wide variety of vertebrates, is the agent responsible for Chagas' disease. This pathology often results in severe inflammatory heart condition and it is one of the major causes of dilated cardiomyopathy leading to heart failure in Latin America. Nevertheless, little is known about the changes in isolate cardiac myocytes contractility during the development of this pathology. Here we report a relationship between cytokines profile of mice infected with T. cruzi and the modifications in the cellular contractility pattern. We found that cellular contractility, measured as fractional shortening, showed a complex behavior. The changes were evaluated during the acute phase (15, 30 and 45 dpi) and chronic phase (>90 dpi). The time to half contraction and relaxation were lengthier despite the number of days after infection or the heart region evaluated. The maximal contraction and relaxation velocities were significantly slower. The observed changes in cellular contractility were correlated with the presence of circulating IFN-gamma, TNF-alpha and MCP-1/CCL2 during the course of infection. Together, our data demonstrate that cellular contractility is altered in the three heart regions studied, and these alterations are observed at the very beginning of the parasitism and they remained until the chronic phase has been reached. Indeed, we propose a role for IFN-gamma, TNF-alpha and MCP-1/CCL2 in the mechanical heart remodeling during experimental Chagas' disease.

Investigation of the cardiomyocyte dysfunction in bradykinin type 2 receptor knockout mice.

AIMS: Bradykinin type 2 receptor (B(2)R) is the key component to trigger the intracellular signaling pathway in response to bradykinin under physiological conditions. The present study sought to investigate whether the B(2)R gene deletion will have an impact on myocardial function. MAIN METHODS: Isolated cell shortening, patch-clamp technique, Western blot and confocal microscopy. KEY FINDINGS: Isolated cell shortening measurements showed significant reduction in B(2)R knockout (B(2)R(-/-)) left ventricular cardiac myocytes' shortening. Whole-cell recordings were used to study the electrophysiological aspects of the left ventricular B(2)R(-/-) cardiomyocytes. Results showed: 1) action potential lengthening; 2) unchanged inwardly rectifying K(+) current; 3) reduced transient outward K(+) (I(to)) and L-type Ca(2+) current densities; 5) changes in kinetic properties related to I(to) and I(Ca,L). In addition, transient sarcoplasmic reticulum (SR) Ca(2+) release was found to be smaller in B(2)R(-/-) cardiomyocytes. Importantly, evidence is provided that NO constitutive production is, at least in part, responsible for the reported electrophysiological modifications observed in cardiomyocytes from B(2)R(-/-) mice. Surprisingly, NO is not involved in the SR Ca(2+) release reduction as demonstrated in the present study. SIGNIFICANCE: Taken together, our findings indicate that B(2)R plays a fundamental role in the regulation of cardiac function and Ca(2+) homeostasis, probably through a NO dependent pathway. These results may contribute to our understanding of the kinins participation in the control of cardiac function.