Norepinephrine and serotonin increase the vasoconstrictor response of the perfused rat tail artery to changes in cytosolic Ca2+.

Vasoconstriction and changes in cytosolic free Ca2+ concentrations (fura 2 with dual wavelength excitation) were measured simultaneously in the perfused tail artery of the rat. Vasoconstrictors (norepinephrine and 5-HT) appear to modulate contraction not only by changing the cytosolic free Ca2+ concentration but also by modifying the sensitivity of the contractile proteins to Ca2+.