In Vitro Activation of Smooth Muscle from the Hog Carotid Artery

Abstract

Very few precise quantitative studies exist on the mechanical properties of vascular smooth muscle (VSM). The lack of data required for an understanding of the basic contractile system in VSM is largely due to the difficulty of obtaining suitable muscle preparations. An arterial smooth muscle preparation obtained from the media of hog carotid arteries was recently developed (1), which because of its large muscle fraction, uniform longitudinal cell orientation, and absence of adventitial connective tissue is well suited for in vitro mechanical and biochemical studies. The purpose of the present study was to characterize the response of this preparation to a variety of stimulating agents of physiological significance, and to differentiate direct actions from neurally mediated contractile responses.

Methods and Materials. Carotid arteries were obtained from hogs 20-60 min after slaughter and immediately immersed in ice-cold physiological salt solution (PSS) (composition given below). After removing loose adventitia, the arteries were stored in fresh PSS at 4° until used. Vascular strips were teased from hog carotid arteries as described previously (1). They were mounted vertically between two stainless steel clips. One clip was attached to a Grass FT.03 strain gauge by a stainless steel jewelry chain and the other was connected to a glass rod mounted on a micrometer. The strips were stimulated electrically at 15 min intervals until a constant isometric contractile response was obtained. Force was recorded by a Grass Model 7 Polygraph, and length could be determined by means of the micrometer. Bath temperature was regulated at 37°. The composition of the bathing solution was (mM): NaCl, 119; KCl, 4.7; KH₂PO₄, 1.18; MgCl₂, 1.17; NaHCO₃, 14.9; dextrose, 5.5; CaNa₂-ethylenediaminetetraacetic acid (EDTA), 0.026; CaCl₂, 1.6. The solution was bubbled continuously with 95% O₂ + 5% CO₂ giving a pH of 7.4.