Increased Vascular Smooth Muscle Contractility in TRPC6^−/− Mice

Abstract

Among the TRPC subfamily of TRP (classical transient receptor potential) channels, TRPC3, -6, and -7 are gated by signal transduction pathways that activate C-type phospholipases as well as by direct exposure to diacylglycerols. Since TRPC6 is highly expressed in pulmonary and vascular smooth muscle cells, it represents a likely molecular candidate for receptor-operated cation entry. To define the physiological role of TRPC6, we have developed a TRPC6-deficient mouse model. These mice showed an elevated blood pressure and enhanced agonist-induced contractility of isolated aortic rings as well as cerebral arteries. Smooth muscle cells of TRPC6-deficient mice have higher basal cation entry, increased TRPC-carried cation currents, and more depolarized membrane potentials. This higher basal cation entry, however, was completely abolished by the expression of a TRPC3-specific small interference RNA in primary TRPC6^−/− smooth muscle cells. Along these lines, the expression of TRPC3 in wild-type cells resulted in increased basal activity, while TRPC6 expression in TRPC6^−/− smooth muscle cells reduced basal cation influx. These findings imply that constitutively active TRPC3-type channels, which are up-regulated in TRPC6-deficient smooth muscle cells, are not able to functionally replace TRPC6. Thus, TRPC6 has distinct nonredundant roles in the control of vascular smooth muscle tone.

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Increased Vascular Smooth Muscle Contractility in TRPC6−/− Mice

ACKNOWLEDGMENTS

We thank Sumit Sen for the initial characterization of P1 clones and Guylain Boulay, Meisheng Jiang, and Karsten Spicher for their technical advice during the production and breeding of TRPC6-deficient mice. We also thank Tim Plant for helpful discussion and critical advice on the manuscript. The help of Heribert Nau, Kim Ngo, and Rafi Salibian in the genotyping of mice is greatly acknowledged. We are grateful to Christan Walther for his initial help in preparing smooth muscle cells from cerebral arteries and Serdar Sel and Berit Schuhmann for their support in performing light cycler experiments. The excellent technical assistance of Sabine Grüger, Diana Herold, Ilona Kamer, and Winfried Lorenz is greatly appreciated.

This work was supported by the Deutsche Forschungsgemeinschaft (A.D., T.G., and M.G.) and by a grant from the National Heart, Lung and Blood Institute, U.S. Department of Health and Human Services, to L.B. (HL-45198).