Contractile response of the myocardium of cardiac patients to chemical scarification of the cell membrane

Abstract

Strips of myocardium from the auricles of the hearts of patients with mitral stenosis (MS) and patients with cardiac septal defects (CSD) were treated with a solution of EDTA (3 mM) to increase the permeability of the cell membrane (scarification). In a 3 mM solution of ethylene-hexaminetetraacetic acid (EHTA), against the background of increased permeability of the membrane to the Ca-EHTA complex, whereby the Ca²⁺ concentration in the myofibrils can be regulated between 10⁻⁹ and 10⁻⁴ M, a mechanical response of the contractile proteins to a change in Ca²⁺ concentration was recorded. Despite identical threshold concentrations (5·10⁻⁸ M) and saturation concentrations (10⁻⁴ M) of Ca²⁺, strips from patients with MS were found to develop a maximal force per unit cross section of the strip only half as high as preparations from patients with CSD, which suggests a probable lesion of the contractile proteins in the hearts of patients with MS. The ratio between the amplitudes of contraction under conditions of complete calcium activation of the contractile proteins and a single isometric contraction for preparations obtained from patients with MS was 8–10 and from patients with CSD 4–5. It is suggested that this is the result of more profound changes in the apparatus of electromechanical coupling of the myocardium of patients with MS.