W. Hamelink, B.W. Treijtel, F.A.M. van Kaam, P.L.T.M Frederix, T.Blangé
Department of Physiology, University of Amsterdam, The Netherlands
Calcium-channel antagonists are reported to enhance tension in skinned skeletal and heart muscle fibres due to increase in stiffness of the actin-myosin interaction site. These antagonists influence the cooperativity of the two different types of binding sites on troponin-C (low- and high-affinity sites). (Schiereck et al.,1993) In this study we examine the effect of two antagonists, diltiazem and isoptin, in an in vitro motility assay with (regulated) actin filaments sliding over a myosin-coated coverglass. Experiments are in progress on measuring an effect on the filament velocity. Subsequently the effect of the antagonists will be studied when putting the actin filament under load. For this purpose we use an in vitro motility assay in which force is applied to magnetisable beads (Dynabeads) attached to actin filaments. The force applied to the Dynabeads is controlled by current through an electromagnet and is constant over the field of view in the plane of the moving filaments. A value of more than 50pN can be reached, while forces in z-direction are still negligible.