Calcium-dependent stress maintenance without myosin phosphorylation in skinned smooth muscle

Stress development depended on calcium-stimulated myosin phosphorylation in an arterial smooth muscle preparation in which the concentration of calcium was controlled. However, developed stress was maintained at a concentration of calcium that did not support phosphorylation. These results, in conjunction with other evidence, suggest that the interaction of two regulatory mechanisms with different calcium sensitivities regulate both stress and the rate and energetics of contraction.     

Phosphorylation of myosin light chains in mouse fast-twitch muscle associated with reduced actomyosin turnover rate

Phosphorylation of the 18,000-dalton light chains of the fast-twitch myosin in mouse extensor digitorum longus muscles was correlated with reduction in the rate of the actomyosin adenosinetriphosphatase in vivo, but neither of these changes occurred in the soleus muscle. These results suggest that actomyosin interactions can be down-regulated by a reversible covalent modification of myosin light chains, that a mechanism for thick-filament regulation occurs in vertebrate skeletal muscle, and that the expression of this regulation may be limited to a specific fiber type.     

Increased phosphorylation of myosin light chain kinase after an increase in cyclic AMP in intact smooth muscle

The role of cyclic adenosine monophosphate-mediated phosphorylation of myosin light chain kinase in relaxing smooth muscle was examined. The kinase was immunoprecipitated from tissue extracts and the phosphate content was determined. The addition of forskolin to resting or methacholine-contracted muscles resulted in an increase in myosin light chain kinase phosphorylation of myosin light chain kinase is one of the reactions in the process by which cyclic adenosine monophosphate causes relaxation of smooth muscle.     

Phosphorylation of muscle membranes: identification of a membrane-bound protein kinase

A membrane-bound protein kinase occurs in membranes derived from rat skeletal muscle and appears limited to a surface membrane fraction. The enzyme is magnesium dependent, is only minimally stimulated by cyclic nucleotides, and phosphorylates serine and to a lesser extent threonine residues of three membrane proteins with molecular weights of less than 30,000.     

Contraction of granulation tissue in vitro: similarity to smooth muscle

Strips of granulation tissue from three different experimental models contract in vitro when treated with substances that induce contraction of smooth muscle. Because the fibroblasts in such tissues have some ultrastructural features typical of smooth muscle, our findings indicate that fibroblasts are able to modulate toward a cell type that is morphologically and functionally close to smooth muscle.     

Muscle relaxation: evidence for an intrafibrillar restoring force in vertebrate striated muscle

Observations of contracting muscle fibrils in cultured cells indicate that the force which restores the resting length of the sarcomere comes from the contractile elements themselves and not from external elasticity, as is now generally accepted. In light of biochemical studies on the contraction-relaxation cycle, it is postulated that the elongating force is one of internal elasticity in the sarcomere, which arises during contraction from the distortion of bonds between filaments and/or structural proteins. This mechanism of restoration may serve to establish optimal sarcomere length for production of maximum contractile force, and in cardiac muscle this mechanism may be a factor in ventricular filling.     

Angiotensin II: rapid localization in nuclei of smooth and cardiac muscle

Five to ten nanograms of labeled angiotensin II rapidly injected in the left ventricle of adult rats was found to induce significant ultrastructural endothelial changes, resulting in net increases in number and size of pinocytotic vesicles as well as widening of intercellular spaces. This effect was followed by preferential localization of the compound in the nuclear zone of vascular and cardiac muscle cells. The selective cellular localization of angiotensin II suggests that this vasoactive agent or some of its metabolic fragments may have specific effects on nuclear function.     

Localization of calcium pump activity in smooth muscle

A microsomal fraction isolated from longitudinal smooth muscle of guinea pig ileum actively sequesters calcium ion in the presence of magnesium and adenosine triphosphate in a fashion previously described for microsomes of the rabbit aorta. This activity in guinea pig ileum appears to be associated primarily with the plasma membrane as is found in the red cell. By contrast the uptake of calcium in aortic smooth muscle appears to be associated to an appreciable extent with intracellular membranes, possibly analogous to the sarcoplasmic reticulum of skeletal muscle.     

Cytosolic-free calcium transients in cultured vascular smooth muscle cells: microfluorometric measurements

Microfluorometric recordings were made of changes in the concentration of cytosolic-free calcium in cultured rat vascular smooth muscle cells treated with quin 2, an intracellularly trapped dye, under several conditions. Nitroglycerin decreased calcium in both the presence and absence of extracellular calcium and strongly and progressively decreased the extent of transient increases in calcium induced by repeated applications of caffeine in the absence of extracellular calcium. Therefore nitroglycerin probably decreases cytosolic-free calcium by accelerating the extrusion of calcium through the sarcolemmal membrane.     

Cyclic adenosine monophosphate: potassium-dependent action on vascular smooth muscle membrane potential

Dibutyryl cyclic adenosine monophosphate and theophylline hyperpolarize smooth muscle of rabbit main pulmonary artery in low concentrations of potassium (1 millimole per liter) but do not have a significant effect on the membrane potential in the presence of high concentrations of potassium (10 millimoles per liter). The dependence of the hyperpolarizing effect on a low external concentration of potassium is similar to that observed with isoproterenol. Prior treatment with theophylline potentiated the hyperpolarizing action of isoproterenol. These findings are compatible with the assumption that potassium-dependent, beta-adrenergic hyperpolarization is mediated by cyclic adenosine monophosphate.     

Regulation of calcium concentration in voltage-clamped smooth muscle cells

The regulation of intracellular calcium concentration in single smooth muscle cells was investigated by simultaneously monitoring electrical events at the surface membrane and calcium concentration in the cytosol. Cytosolic calcium concentration rose rapidly during an action potential or during a voltage-clamp pulse that elicited calcium current; a train of voltage-clamp pulses caused further increases in the calcium concentration up to a limit of approximately 1 microM. The decline of the calcium concentration back to resting levels occurred at rates that varied with the calcium concentration in an apparently saturable manner. Moreover, the rate of decline at any given calcium concentration was enhanced after a higher, more prolonged increase of calcium. The process responsible for this enhancement persisted for many seconds after the calcium concentration returned to resting levels. Thus, the magnitude and duration of a calcium transient appear to regulate the subsequent calcium removal.     

Cat hemoglobin: pH-dependent cooperativity of oxygen binding

Cat hemoglobin has a lower cooperativity and oxygen affinity than most mammalian hemoglobins. In contrast to the usual invariance of cooperativity with pH, a rise in cooperativity with pH is predicted by the allosteric model for low-affinity hemoglobins. Such a pH-dependent cooperativity for cat hemoglobin has been found.     

Continued expression of neonatal myosin heavy chain in adult dystrophic skeletal muscle

The expression of myosin heavy chain isoforms was examined in normal and dystrophic chicken muscle with a monoclonal antibody specific for neonatal myosin. Adult dystrophic muscle continued to contain neonatal myosin long after it disappeared from adult normal muscle. A new technique involving western blotting and peptide mapping demonstrated that the immunoreactive myosin in adult dystrophic muscle was identical to that found in neonatal normal muscle. Immunocytochemistry revealed that all fibers in the dystrophic muscle failed to repress neonatal myosin heavy chain. These studies suggest that muscular dystrophy inhibits the myosin gene switching that normally occurs during muscle maturation.     

Vascular smooth muscle: aerobic glycolysis linked to sodium and potassium transport processes

Under aerobic conditions, glucose is primarily catabolized by vascular smooth muscle to lactate, in spite of an adequate oxidative capacity. Although this is often considered to be indicative of some nonspecific metabolic insufficiency, there is evidence that aerobic glycolysis is specifically coupled to sodium and potassium transport processes, whereas oxidative metabolism is couple to contracticle energy requirements.     

Antagonistic adrenergic-muscarinic regulation of M current in smooth muscle cells

The beta-adrenergic agonist isoproterenol and analogs of adenosine 3',5'-monophosphate (cAMP) induced a potassium current, M current, in freshly dissociated gastric smooth muscle cells. Muscarinic agonists suppress this current, apparently by acting at a locus downstream from regulation of cAMP levels by adenylate cyclase and phosphodiesterase. Thus, M current can be induced by an agent and regulated in antagonistic fashion by beta-adrenergic and muscarinic systems.     

Cooperative critical thermal transition of potassium accumulation in smooth muscle

The steady-state levels of potassium and sodium of taenia coli of guinea are critically affected by varying temperature in the narrow range 12 degrees to degrees C. For the accumulation of both cations the critical temperature, T(c), is 13.8 degrees C the presence of millimolar external potassium. The value of T(c), decreases 10.0 degrees C when the external potassium is raised to 10 millimolar. Since, at a fixed Temperature, the potassium accumulation follows a cooperative mechanism, the results are compared with the quantitative predictions of this approach. The itical thermal transition behavior can be described in terms of the cooperative cumulation process.