Length-Tension Relationship of Smooth Muscle of the Hog Carotid Artery

Abstract

The length-tension relationships for arterial smooth muscle were determined using vascular strips teased from the media of hog carotid arteries. Histological examination revealed that the strips were (1) free of adventitia and (2) composed of smooth muscle cells oriented parallel to the long axis of the strips. Measurements from electron micrographs indicated that 60% of the cross-sectional area consisted of smooth muscle. At L₀ (the optimal length for tension development) the total cross-sectional area of the strips varied from 0.3 to 0.8 mm². Potassium-induced depolarization was the most effective stimulus for force development. Norepinephrine and electric field stimulation elicited responses which were 70% and 30%, respectively, of that produced by potassium-induced depolarization. At L₀ the intrinsic load-bearing capacity (P₀) of the contractile system was 2.22 x 10⁶ dynes/cm². Tension development fell off gradually at lengths shorter than L₀ and more rapidly at lengths greater than L₀. Passive length-tension curves were determined after quick releases from higher to lower lengths to avoid complications arising from tone. Passive tension was negligible at lengths below 0.9 L₀. At L₀ the passive tension was 10% of P₀.