CHANGES IN THE CALDESMON ISOFORM CONTENT AND INTIMAL THICKENING IN THE RABBIT CAROTID-ARTERY INDUCED BY A SILICONE ELASTOMER COLLAR

The presence of a silicone elastomer collar around one carotid artery of a rabbit induces thickening of the tunica intima. We used immunoblo tting to study quantitatively changes in the isoforms of caldesmon, a protein implicated in the regulation of contractility in smooth muscle , while also monitoring the histological changes during 28 days after collaring. Control rabbit carotid arteries (n=28) contained 245+/6.4 n mol/g protein of the larger isoform of caldesmon (CDh) and 68.3+/-3.6 nmol/g protein of the smaller isoform (CDl). Four days after collaring , intimal thickening was slight, but 44% of arterial CDh had been lost ; this loss of CDh was therefore from the tunica media. At 10 days, CD h fell to 37% of the control level. Immunofluorescence using CDh-speci fic antibodies showed that the CDh level was diminished but remained u niform across the wall of collared arteries. At 14 days, when intimal thickening was maximal, there was 30% more CDl than in controls. At 28 days, the neointima had thinned, and CDl had fallen to below control levels. Thus, CDl levels reflected the development and regression of n eointima. Changes in caldesmon isoforms showed that smooth muscle cell phenotypic changes occurred throughout the arterial wall.