Abstract
To investigate the contractile properties of young (4-5 weeks) mouse cardiac ventricular cells, we isolated ventricular cells from 4-5 weeks mice. Ventricular cells were transffered to a non-fluorescent glass chamber, mounted on the stage of an inverted microscope (Eclipse TE2000, Nikon, Japan). Cell length was captured through an objective lens with either 20x or 40x magnification (Fluor 20x, SFluor 40x, Nikon, Japan). Cell shortening was detected with a MyoCam CCD camera at a speed of 60 Hz. The video-monitored data were digitized through a DSI 1200 computer interface (IonOptix, USA) and were analyzed by a video-edge-detection system (IonOptix, USA). Electrical field stimulation (15 V, 10 ms) was applied through a silver electrode placed near the cell. When extracellular calcium concentration ([Ca]o)was 0.9 mM, myocytes showed the negative staircase of cell shortening at a stimulation frequency of 0.2, 0.5, and 1 Hz. At a stimulation frequency of 0.1 Hz or less, the degree of cell shortening was constant. We then investigated the effecct of [Ca]o on the negative staircase of cell shortening. At [Ca]o of less than 1.8 mM, the cells showed the negative staircase. However, at [Ca]o of greater than 2.5 mM, the negative staircase disappeared. These results suggest that stimulation frequency and [Ca]o are to be considered to evaluate contraction or calcium dynamics in genetically engineered mouse cardiac myocytes. [Jpn J Physiol 54 Suppl:S122 (2004)]
