Effects of amrinone on shortening velocity and force development in skinned skeletal muscle fibres

Abstract

The effects of amrinone were studied on single skinned fibres isolated from rat hindlimb muscles. In each fibre a force-velocity relation was determined during maximal calcium activation (pCa = 4.45) in control conditions and in the presence of amrinone. The MgATP concentration was 3.93 mM, close to the physiological value. After the experiment the fibre was classified as fast or slow on the basis of its reactivity with anti-myosin monoclonal antibodies. In fast fibres amrinone (3 mM) potentiated isometric tension (Po) by 13.8 +/- 2.9% (n = 13), reduced maximum shortening velocity (Vmax) by 32.6 +/- 3.2% and the curvature of the force-velocity relation (a/Po) was increased by 98.9 +/- 46.0%. All these effects were less pronounced in slow fibres, where Vmax was reduced only by 11.4 +/- 3.6 (n = 16). The effects of amrinone (0.3-6 mM) on the ATPase activity of myofibrils and myosin prepared from fast (tibialis anterior) and slow (soleus) rat skeletal muscles were studied. Amrinone was found to depress Ca-Mg dependent ATPase activity of myofibrillar preparations of the tibialis anterior (up to 16.6 +/- 2%) and, to a lesser extent, of the soleus (up to 7.2 +/- 1.2%). On the contrary, Ca-stimulated myosin ATPase activity was significantly increased by amrinone in myosin preparations from the tibialis anterior. Experiments were carried out to test whether amrinone (3 mM) might affect the sensitivity of the contractile system to MgATP concentration ([MgATP]). The results obtained showed that (1) the [MgATP] value at which isometric tension reached its maximum was shifted by amrinone from 0.1 mM to 0.3 mM, (2) the slope of the negative relation between [MgATP] and a/Po was made more steep by amrinone, and (3) the Km of the hyperbolic relation between [MgATP] and Vmax was increased from 0.39 to 1.71 mM by amrinone, thus indicating a reduced affinity of myosin for MgATP. These results are in accordance with the hypothesis that amrinone exerts a direct effect on the contractile mechanism.

Drug Effect Unveils Inter-head Cooperativity and Strain-dependent ADP Release in Fast Skeletal Actomyosin

“…In all the fast myosin preparations, the effect of about 1 m m amrinone on isometric force was associated with characteristic changes of the force-velocity relationship (Fig. 1 B ), including a reduced maximum velocity of shortening (19–22) and a reduced curvature of the force-velocity relationship (19–22). The latter effect was accompanied (20, 21) by a less pronounced deviation of the force-velocity relationship from the hyperbolic shape (23) at high loads.…”

“…1 A ) has been found to increase the isometric force production of fast intact skeletal muscles of the frog (19, 20) and mouse (21) and also of fast (but much less slow) skinned muscle fibers of the rat (22). In all the fast myosin preparations, the effect of about 1 m m amrinone on isometric force was associated with characteristic changes of the force-velocity relationship (Fig.…”

“…There have been different interpretations of the drug effects. It has been proposed (20–22) that amrinone might competitively inhibit the MgATP binding by myosin. However, more recently, results from in vitro motility assay experiments (24) challenged this idea.…”

A novel method for the synthesis of 1(2H)‐phthalazinones using silica‐supported perchloric acid

“…Phthalazine scaffold have shown its potential as a privileged structure for the generation of drug-like libraries in drug-discovery process [2]. 2H-Phthalazin-1-ones are of considerable interest due to their antidiabatic [3] and antiallergic activities [4], and its bioactivity has been researched extensively [5][6][7][8]. They are also useful intermediates for the synthesis of inhibitors of the VEGF (vascular endothelial growth factor) receptor tyrosine kinases for the treatment of cancer [9].…”

Crystal structure, antitumor activities and DNA-binding properties of the La(III) complex with Phthalazin-1(2H)-one prepared by a novel route

“…Phthalazin-1(2H)-one was synthesized many years ago [14], its bioactivity has been researched extensively [15][16][17][18][19]. However, its rare earth complexes seem not to be reported.…”