RESUMEN
Changes in the muscle tissue stiffness are important and necessary signs of the contractile process. The work is devoted to the study of this parameter of the smooth muscle tissue reaction during the action of phorbol esters, (namely, phorbol 12-myristate 13-acetate (PMA)), synthetic imitators of diacylglycerole. The experiments were carried out on isolated native preparations of aorta thoracic area of guinea pig under isometric conditions. Contraction induced by PMA or by the temperature was not accompanied by the stiffness changes. Potassium contraction (its development, amplitude, relaxation) evoked on the plateau of the PMA-induced contraction was similar in all respects to that in control: the stiffness increased significantly. These findings prove independent development of these two types of contractile processes. At the same time, the stiffness invariability and similar ratios of optical density to mechanical strength changes in the contractions induced by PMA action or by temperature show the likeness of the force generation mechanisms in these mechano-chemical reactions. The results obtained cannot be explained in terms of the generally accepted hypothesis of actomyosin interaction. The conclusion is made that phorbolic esters during the action on the smooth muscle tissue activate the mechanical strength generation by the connective tissue matrix.