Tropomyosin-caldesmon/actomyosin systems in platelets and arterial smooth muscle: results from exchange experiments

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Abstract

Tropomyosin and caldesomon reciprocally control the actomyosin system in smooth muscle and some non-muscle cells. To compare this mechanism between arterial smooth muscle and platelets, we carried out extensive exchange experiments. Actin, myosin, tropomyosin from arterial smooth muscle cells and platelets were recombined and the effects of two species of caldesmon (‘caldesmon77’ and ‘caldesmon140’) on the ATPase activities of both systems were examined and analyzed by the method of analysis of variance. (a) The actomyosin system itself is different between artery and platelets, the difference being determined by myosin (P<0.05) and not by actin. (b) Platelet tropomyosin differentiates platelet actin from arterial actin (P<0.01), while arterial tropomyosin does not. Neither does tropomyosin differentiate myosin. (c) The effect of caldesmon77 differentiates the origins of myosin (P<0.01), actin (P<0.05) and tropomyosin (P<0.05). The effect of caldesmon140 differentiates the origin of myosin (P<0.05) and the actin-myosin ‘interaction’ (combination) (P<0.01), but not the origin of tropomyosin (P>0.1). (1) It is concluded that actomyosin/tropomyosin-caldesmon system is distinguishable between platelets and artery. (2) It is suggested that caldesmon is an actomyosin inhibitor which may interact with myosin, in addition to actin and tropomyosin.

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