Long-term effects of verapamil on aortic smooth muscle cells cultured in the presence of hypercholesterolemic serum.

Smooth muscle cells derived from rabbit and bovine aorta were cultured for up to 5 weeks in the presence of d less than 1.019 g/ml fraction of hypercholesterolemic rabbit serum. When this fraction was added to serum containing culture medium, there was a significant increase in DNA, protein, and cholesteryl ester per dish. Addition of 50 microM verapamil markedly reduced the stimulatory effect of the d less than 1.019 g/ml fraction on both DNA and protein content per dish. The effect of verapamil on cholesteryl ester content was more complex: there was an increase within the first week, but later the net accumulation of cholesteryl ester per dish was lower than in untreated dishes. The recovery of less DNA in verapamil-treated dishes was not due to increased cell loss, as evidenced by retention of a residualizing marker, 3H-cholesteryl linoleyl ether. Moreover, verapamil did reduce incorporation of 3H-thymidine into DNA. In verapamil-treated dishes, there was flattening and a cobblestone appearance of the cells. A hypothesis is proposed to explain the inhibitory effect of verapamil on the development of atheroma formation in cholesterol-fed rabbits: Assuming that macrophages play an active role in cholesteryl ester removal from atheroma, verapamil, which reduces lysosomal cholesteryl ester hydrolysis in macrophages, would permit the lipid-laden macrophage to remove more cholesteryl ester per cell from the arterial wall. In addition, the presently reported results support the possibility that verapamil may impede the development of atheroma formation by reduction of smooth muscle cell proliferation.