Characteristics of Ca2+- and Mg2+-induced tension development in chemically skinned smooth muscle fibers.

Abstract

A B S T R A C T Chemically skinned fibers from guinea pig taenia caecum were prepared by saponin treatment to study the smooth muscle contractile system in a state as close to the living state as possible. The skinned fibers showed tension development with an increase of Ca 2+ in the solution, the threshold tension occurring as 5 x 10 -7 M Ca 2 § The maximal tension induced with 10 -4 M Ca 2+ was as large and rapid as the potassium-induced contracture in the intact fibers. The slope of the pCa tension curve was less steep than that of skeletal muscle fibers and shifted in the direction of lower pCa with an increase of MgATP. The presence of >1 mM Mg 2+ was required for Ca2+-induced contraction in the skinned fibers as well as for the activation of ATPase and superprecipitation in smooth muscle myosin B. Mg 2+ above 2 mM caused a slow tension development by itself in the absence of Ca 2 § Such a Mg2 § tension showed a linear relation to concentrations up to 8 mM in the presence of MgATP. Increase of MgATP concentration revealed a monophasic response without inhibition of Ca2+-induced tension development, unlike the biphasic response in striated muscle. When MgATP was removed from the relaxing solution, the tension developed slowly and slightly, even though the Mg ~+ concentrations was fixed at 2 mM. These results suggest a substantial difference in the mode of actin-myosin interaction between smooth and skeletal muscle.

Effects of diltiazem on calcium concentrations in the cytosol and on force of contractions in porcine coronary arterial strips

“…This suggests that receptor-mediated stimulation increased Ca2+-sensitivity of the contractile apparatus (Morgan & Morgan, 1984;Bruschi et al, 1988;Himpens & Somlyo, 1988;Rembold & Murphy, 1988;Sato et al, 1988). In addition, the [Ca2 t]i-tension relationship of the Ca2 '-induced contraction during depolarization was similar to the pCa-tension relationship noted with skinned fibres of the porcine coronary artery and of others (Saida & Nonomura, 1978;Kuriyama et al, 1982). (Matsumoto et al, 1989).…”

“…To assess the relationship between Ca2+ concentrations and tension development, mechanically or chemically skinned muscle strips have been used. In such cases, sarcolemmal signal transduction systems might be seriously damaged (Saida & Nonomura, 1978;Kuriyama et al, 1982).…”

Role of extracellular and intracellular sources of Ca2+ in sarafotoxin S6b‐induced contraction of strips of the rat aorta

“…When tissues were exposed to 10;EM H-7, the Ca2"-independent contraction induced by sarafotoxin after a 60 min exposure to Ca2"-free solution was inhibited by 83.6 ± 3.7% (n = 3). (Figure 7) was similar to the pCa-force relationship noted with skinned arterial fibres of various species and organs Saida & Nonomura, 1978;Kuriyama et al, 1982 (Rasmussen et al, 1987;Murphy, 1989 Hirano et al, 1990). In the present study, we used front-surface fluorometry of fura-2 loaded rat aortic strips to examine the roles of extracellular and intracellular Ca2" and of the [Ca2+]J-force relationship in contractions induced by sarafotoxin.…”

Mechanisms underlying the neurokinin A‐induced contraction of the pregnant rat myometrium

“…The strips were permeabilized in a relaxing solution (mM): potassium methanesulphonate 100, Na 2 ATP 2.2, MgCl 2 3.38, ethyleneglycol-bis (b-aminoethylether)-N',N',N',N'-tetra acetic acid (EGTA) 10, creatine phosphate 10, Tris-maleate 20 (pH=6.8) containing 5000 units ml 71 Staphylococcus aureus a-toxin for 60 min. The activating solution containing the indicated concentration of free Ca 2+ was made by adding an appropriate amount of CaCl 2 to the relaxing solution, using the Ca 2+ -EGTA binding constant of 10 6 /M (Saida & Nonomura, 1978). The tension measurements of the permeabilized tissue were all performed at room temperature.…”