Dual contractile response of the aorta strip

Abstract

Isotonic contractions of rabbit aorta strips recorded in response to chemical stimuli strongly suggest that the shortening process has a dual character, consisting of a fast (F-) and a slow (S-) component. In the current study evidence for a dual contractile mechanism was sought by attempting to separate one component from the other. The S-component is more altered than the F-component by shifts in electrolyte composition. The S-component is less activated than the F-component by low concentrations of epinephrine or norepinephrine. The F-component is less activated than the S-component by low concentrations of phenylephrine or isopropylarterenol. The differential effect of reduced temperature is the same as that produced by a decrease in concentration of the constrictor. Dibenamine blockade permits a differentiation of the two components since it seems to alter the ratio of available receptors which activate the two components. When norepinephrine was used in high concentrations after Dibenamine blockade it caused a separation of the F- and S-components by imposing a period of relaxation between the two.