Calcium‐ and length‐dependent force production in rat ventricular muscle

Abstract

1. Trabeculae from the right ventricles of rat hearts were ‘skinned’ by immersion for 30 min in a solution containing the non‐ionic detergent Brij‐58 at a concentration of 1%. 2. The average sarcomere length in the central region of the relaxed preparation was estimated by laser diffraction and set at pre‐determined values within the range of 1·9‐2·4 μm by adjustment of muscle length. Isometric contractions were then induced by raising the Ca 2+ concentration under carefully controlled chemical conditions. 3. The dependence of Ca 2+‐activated force production on sarcomere length over the ascending limb of the length—force relation was examined at Ca 2+ concentrations giving partial and full activation of the contractile system of the muscle. 4. The dependence of Ca 2+‐activated force on Ca 2+ concentration was compared at sarcomere lengths on the ascending limb and plateau of the length—force relation. 5. The results obtained from both kinds of experiment showed that the sensitivity of the contractile system to Ca 2+ increases with sarcomere length over the ascending limb of the length—force relation. 6. Possible explanations for this observation have been discussed.