RESUMEN
The contractile response to Endothelin-1 (ET-1) has been investigated in electrically stimulated single cardiac myocytes isolated from hearts of young and senescent rats. ET-1 (0.1-10 nM) exhibited a marked negative inotropic effect in both age groups. ET-1 (1.0 nM) also reduced the occurrence of spontaneous contractile oscillations in young myocytes, suggesting depletion of sarcoplasmic reticulum-Ca(2+) stores. The possibility that ET-1 may have opposite effects on myocardial contractility is discussed.
RESUMEN
In recent years methods for the isolation of cardiac myocytes have gained increasing interest. Single cardiac cells represent an effective model for the study of cardiac contractility thanks to their features of simplified preparation. This improves the understanding of cardiac contractile properties and the effects of cardio-active substances. Moreover, it has been demonstrated that the isolation procedure does not alter the basic characteristics of the original tissue. The contractility indices in multicellular models are derived from the direct measurement of mechanical parameters (pressure and tension). These are difficult to perform in the case of isolated cardiac myocytes for which optical techniques of measurement proved particularly suitable. A system based on the video motion detector technique has been used to measure the extent of shortening. The cell is observed using a video camera connected with a phase contrast microscope. The video dimension analyser receives the cell image from the video camera and its output is a voltage proportional to the cell length. This signal is sent to a personal computer for acquisition and analysis. The signal is then digitalized by an analog to digital conversion board and subsequently elaborated to calculate the contraction parameters. Then these values are visualized on the computer screen, printed and stored with other pertinent information typed by the user. The result is the creation of a data file, available for further processing.