Uniform sarcomere behaviour during twitch of intact single cardiac cells

Behaviour of sarcomere length was analysed in different regions of single cardiac cells ( n=249) of the ventricle, both at rest ( n=144) and during twitch contractions ( n=57). At rest, regional distribution of sarcomere length proved to be uniform. In the leaky cell ( n=48), resting sarcomere length was not affected over longer periods of time (up to 2 h), nor by lowering the ATP concentration (from 5 m m to 2.5 m m and 500 μ m), nor by increasing free calcium within subactivating ranges (5, 20, 60 μ m). No statistical differences could be detected between resting cell dimensions and sarcomere length between cells isolated from left and right ventricle ( n=64), nor between cells from epicardial or endocardial layers ( n=80). During twitch contraction in the intact unloaded cardiac cell ( n=32), sarcomere lengths in different regions were analysed every 20 ms and behaved synchronously, presenting arguments for uniformity during the myocardial contraction-relaxation cycle in the free-lying intact cardiac cell.