TRPV2 Is a Component of Osmotically Sensitive Cation Channels in Murine Aortic Myocytes

Abstract

Abstract-Changes in membrane tension resulting from membrane stretch represent one of the key elements in blood flow regulation in vascular smooth muscle. However, the molecular mechanisms involved in the regulation of membrane stretch remain unclear. In this study, we provide evidence that a vanilloid receptor (TRPV) homologue, TRPV2 is expressed in vascular smooth muscle cells, and demonstrate that it can be activated by membrane stretch. Cell swelling caused by hypotonic solutions activated a nonselective cation channel current (NSCC) and elevated intracellular Ca 2ϩ ([Ca 2ϩ ] i ) in freshly isolated cells from mouse aorta. Both of these signals were blocked by ruthenium red, an effective blocker of TRPVs. The absence of external Ca 2ϩ abolished this increase in [Ca 2ϩ ] i caused by the hypotonic stimulation and reduced the activation of NSCC. Significant immunoreactivity to mouse TRPV2 protein was detected in single mouse aortic myocytes. Moreover, the expression of TRPV2 was found in mesenteric and basilar arterial myocytes. Treatment of mouse aorta with TRPV2 antisense oligonucleotides resulted in suppression of hypotonic stimulationinduced activation of NSCC and elevation of [Ca 2ϩ ] i as well as marked inhibition of TRPV2 protein expression. In Chinese hamster ovary K1 (CHO) cells transfected with TRPV2 cDNA (TRPV2-CHO), application of membrane stretch through the recording pipette and hypotonic stimulation consistently activated single NSCC. Moreover, stretch of TRPV2-CHO cells cultured on an elastic silicon membrane significantly elevated [Ca 2ϩ ] i . These results provide a strong basis for our purpose that endogenous TRPV2 in mouse vascular myocytes functions as a novel and important stretch sensor in vascular smooth muscles. Key Words: TRPV2 Ⅲ vanilloid receptor Ⅲ mouse aorta Ⅲ membrane stretch Ⅲ vascular smooth muscle D etection of mechanical stimuli is essential for diverse biological functions including audition, touch, and maintenance of vascular myogenic tone. In the latter, elevation of intravascular pressure depolarizes vascular smooth muscle cells via membrane stretch. 1,2 This depolarization activates voltage-dependent L-type Ca 2ϩ channels (VDCC) and increases [Ca 2ϩ ] i , resulting in vasoconstriction and/or myogenic tone. 3 A large component of the elevation of [Ca 2ϩ ] i by myogenic tone can be inhibited by blockers of VDCC. However, some components are resistant to these agents, and instead can be accounted for by a separate nonselective cation channel that is permeable to Ca 2ϩ and also is activated by the intravascular pressure. 4,5 Because stretchactivated channels play obligatory roles in regulation of the myogenic tone, extensive studies have been performed to identify the molecular entity of these channels. Originally, a yeast MID1 gene product (MID1) was shown to be a eukaryotic stretch-activated channel, because CHO cells expressing MID1 responded to membrane stretch. 6 A member of the transient receptor potential channels (TRP), specifically TRPC6, is sensitive ...

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“…Several vanilloid subtypes have been shown to be important mediators of vascular tone, cerebral blood flow, neointimal hyperplasia, and pulmonary hypertension 11, 12, 13. Expression of the transient receptor potential vanilloid 2 (TRPV2) channel was noted in abundance in murine myocardial tissue, specifically in the left ventricle 14.…”

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