The effect of length on the sensitivity to phenylephrine and calcium in intact and skinned vascular smooth muscle

The length dependency of the sensitivity to activators of the smooth muscle of different blood vessels is not yet fully understood. Muscle preparation s of the aorta, the femoral artery and the portal vein of the rabbit were i nvestigated for the length dependency of the sensitivity to phenylephrine a nd calcium in both intact and triton X-100 skinned preparations. For intact smooth muscles we found that at increased preparation length, the sensitiv ity of contraction was increased. The femoral artery showed the largest eff ect and the portal vein the smallest. In the skinned preparations of the th ree preparations the calcium sensitivity was not dependent on the preparati on length. We conclude that the changes of the sensitivity in intact prepar ations are not caused by changes of the calcium sensitivity of the contract ile proteins.