The effects of vascular smooth muscle caldesmon on force production by 'desensitised' skeletal muscle fibres.

Smooth muscle caldesmon inhibits actomyosin MgATPase in the absence of Ca2+ and is the key regulatory component of Ca2+-regulated thin filaments. We now show that caldesmon can affect contractility as well. Glycerinated skeletal muscle fibres were treated so as to produce substantial contractions without Ca2+ as an activator. Addition of caldesmon caused reductions in force in a concentration- and time-dependent manner. Perfusion with caldesmon concentration for less than 5 min gave up to 48% reduction in isometric tension with a half-maximal effect at 1.5 micron caldesmon. Perfusion with 15 microM caldesmon for 30 min gave an irreversible tension drop.