Downrgulation of L‐type calcium channels increase media thicknes and change smooth muscle phenotype in rat resistance arteries in vivo.

Abstract

The voltage‐gated L‐type Ca channels (LTCCs) are important in smooth muscle excitation‐transcription coupling. We have developed a method for downregulation of the LTCC in rat small mesenteric arteries in vivo by the use of siRNA. Transfection with specific siRNA decreased LTCC expression by ~75%. The downregulated arteries developed reduced wall stress in response to K‐induced depolarization which resembled control arteriess pre‐treated with nifedipine. Changes in wall stress correlated with smaller changes in [Ca2+]i in the arteries downregulated for LTCC. Similar changes were seen with noradrenalin and vasopressin.In contrast to the effect of LTCC blocker chronic treatment, the LTCC downregulated arteries had increase in media thickness in comparison to the controls. The remodeling was associated with phenotypic changes of the VSMCs: contractile phenotype markers (myocardin, tropomyosin 4, smooth muscle myosin heavy chain, smooth muscle α‐actin and h‐caldesmon) were significantly downregulated, while marker genes for the proliferative phenotype (l‐caldesmon and ki‐67) were significantly upregulated. In α‐toxin permeabilized arteries downregulated for LTCC the force development to calcium was reduced compared to control arteries. We conclude that LTCC expression and/or activity are crucial in determining VSMC phenotype as well as the structure of small resistance arteries.