Effect of dinitrophenol on active relaxation of unstriated muscle

Abstract

Some unstriated muscles, such as those of guinea pig uterus and frog stomach muscle, relax without the application of any external force when treated with adrenaline; during such relaxation the oxygen consumption increases. Relaxation is prevented if these muscles are previously asphyxiated or treated with cyanide and can be partially restored with glucose. Asphyxia or cyanide causes relaxation of loaded muscle. On the basis of these experiments it has been suggested that unstriated muscle contains two contractile mechanisms. One is responsible for the phasic response and a kind of tone susceptible to asphyxia and relaxes passively; the other is responsible for the asphyxia-resistant tone, relaxes actively and thus is able to maintain contraction or tension without expenditure of energy.