The implementation of near-isometric contractions of single cardiomyocytes using a digital micromanipulation system

A single isolated cardiac muscle cell, cardiomyocyte, is a reliable experimental model to study intrinsic mechanical properties of the myocardium. To date, there are few reports aimed to examine cell force parameters during isometric contractions for mimicking cell behavior in the intact heart. No studies were conducted to implement isometric contractions of cardiomyocytes using digital systems. This work is devoted to the use of an adaptive feed-forward control approach for a digital micromanipulation system to subject single cardiomyocytes to near-isometric contractions. To overcome the linear time dependence of digital micromanipulator movement we fitted the complex time dependence of the cell length change to an isosceles trapezoid. The developed software initiated outwardly directed trapezoidal countermovement of micromanipulators during cell auxotonic contractions to achieve the cell length near-constant. The preliminary experiments showed that the maximum normalized force during near-isometric contractions was 2.5 times greater compared with auxotonic contractions that corresponds to earlier studies. The developed approach provides a powerful research tool to study cardiac biomechanics at the cell level under in vivo-like conditions.