Responses of single-ventricular myocytes to dynamic axial stretching

Mechano-electrical feedback (MEF) has mainly been studied in isolated single cardiomyocytes using the microelectrode and micropipette techniques, but information regarding its dynamic aspects at the cellular level is limited due to the technical difficulties associated with manipulating single cells and maintaining stable attachment of these devices. To overcome such difficulties, we have combined two experimental methods, namely a carbon fiber technique to hold single myocytes and a ratiometric fluorescence measurement technique to monitor Ca2+ transients or membrane potentials. Following an overview of the experimental technique for stretching myocytes, the results for single rat ventricular myocytes under axial stretching are presented. Ca2+ transients were influenced by the loading conditions and involvement of myofilaments was suspected in regulatory mechanism. Membrane potential measurements during dynamic axial stretching revealed that the action potential duration was prolonged when the stretch was applied during the late phase of twitch contraction, and that depolarization of the resting membrane potential depended on the phase, amplitude and speed of the applied stretch. The amplitude may also modulate the ion selectivity of stretch-activated channels. This combination of the carbon fiber technique with fluorescence measurement could represent a powerful tool for clarifying MEF at the cellular level.