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

Abstract

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%. 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 .mu.m by adjustment of muscle length. Isometric contractions were then induced by raising the Ca2+ concentration under carefully controlled chemical conditions. The dependence of Ca2+-activated force production on sarcomere length over the ascending limb of the length-force relation was examined at Ca2+ concentrations giving partial and full activation of the contractile system of the muscle. The dependence of Ca2+-activated force on Ca2+ concentration was compared at sarcomere lengths on the ascending limb and plateau of the length-force relation. The results obtained from both kinds of experiment showed that the sensitivity of the contractile system to Ca2+ increases with sarcomere length over the ascending limb of the length-force relation. Possible explanations for this observation were discussed.