Role of calcium in the plasticity of venous smooth muscle

Abstract

Helically cut strips from the cat portal vein were arranged for dynamic tension-length studies, and direct recordings obtained of the stress-strain diagrams on an X-Y recorder. Graded doses of norepinephrine were employed to alter the initial length of the strip; plasticity in each case was evaluated in terms of the net work required to complete a stretch cycle, as measured by the area of the stretch "loop." Elevation of the concentration of Ca ion in the external bath was found to increase the plastic resistance to stretch, whether the dominant cation was Na or depolarizing concentrations of K. Similar effects were produced by related cations: Mg, Sr, and Ba. Plastic resistance to stretch was reduced when the Ca concentration was lowered, and almost eliminated when Ca was removed with chelatlng agents. At both low-and high-Ca levels, the correlation of plasticity with Ca concentration persisted throughout a range of tissue lengths produced by activation of the contractile mechanism with norepinephrine. This evidence suggests that the intracellular concentration of Ca ion plays a key role in determining the plastic resistance of smooth muscle to stretch.