Relaxation of mammalian single cardiac cells after pretreatment with the detergent Brij‐58.

Abstract

The influence of load and activation on relaxation of heart muscle was studied. Cardiac cells devoid of functioning sarcolemma were isolated from rat and cat ventricular myocardium. Pretreatment with the detergent Brij-58 destroyed residual sarcoplasmic reticulum function. To analyze the mechanical properties of relaxation in these cells, a new miniature transducer was designed which could simultaneously measure lengths (resolution smaller than 0.2 .mu.m), impose loads and measure force by feedback sensing (resolution of 1 .mu.g). Contraction was induced by ionophoretically released Ca ions. Activation, sequestration of Ca and loading conditions could be controlled independently. The time course of relaxation was governed by the amount of Ca released, and unlike intact preparations from rat or cat heart (but like those from frog), was independent of load and of alterations in load. Relaxation of the cardiac contractile system is determined basically by an activation-dependent mechanism, which is masked by load dependence in intact muscle preparations with a well-developed Ca sequestering membraneous system.