Effect of stress-like concentrations of cortisol on gonadotroph function in orchidectomized sheep

The effects of the small noncatalytic subunit of myosin light chain phosphatase (MLCPsr) on the Ca2+-induced contraction of smooth muscle were investigated in the Triton X-100-permeabilized porcine renal artery. The full-length recombinant chicken MLCPsr obtained by the bacterial expression system induced an additional contraction at a constant Ca2+]i and shifted the Ca2+]i-force relation curve to the left. A deletion mutant containing the N-terminal 78 amino acids of MLCPsr retained the full action, compared with the full-length MLCPsr, while the deletion of this region completely abolished its effect. The process of relaxation was also delayed by the fragment containing the N-terminal 78 amino acids. These results indicated that MLCPsr increases the Ca2+ sensitivity of the contractile apparatus while the N-terminal 78 amino acids are responsible for this effect in vascular smooth muscle.