Troponin Subunits are Expressed in the Rat Afferent Arteriole

Abstract

Vascular smooth muscle cells of the renal afferent arteriole are unusual: they must be able to contract very rapidly in response to a sudden increase in systemic blood pressure, thereby protecting the downstream glomerular capillaries from catastrophic damage. We showed that this could be accounted for in part by exclusive expression, at the protein level, of the “fast” (B) isoforms of smooth muscle myosin II heavy chains in the afferent arteriole, in contrast to other vascular smooth muscle cells such as the rat aorta and efferent arteriole, which express exclusively the “slow” (A) isoforms (Shiraishi M et al (2003) FASEB J 17: 2284–2286). Since contraction of the more rapidly‐contracting striated (skeletal and cardiac) muscles is regulated by the thin filament‐associated troponin (Tn) system, we hypothesized that Tn or a Tn‐like system may exist in afferent arteriolar cells and contribute to the unusually rapid contraction of this tissue in response to increased intraluminal pressure. We examined the expression of TnC (Ca2+‐binding subunit), TnI (inhibitory subunit) and TnT (tropomyosin‐binding subunit) in vascular smooth muscle cells of the rat renal afferent arteriole at the mRNA level. Fast skeletal muscle and slow skeletal muscle/cardiac TnC isoforms and slow skeletal muscle and cardiac TnI isoforms were detected by RT‐PCR and confirmed by cDNA sequencing. Furthermore, cardiac and slow skeletal muscle TnI isoforms, but not fast skeletal muscle TnI were detected in isolated afferent arterioles at the protein level by proximity ligation assay. We conclude that, in addition to Ca2+‐mediated phosphorylation of myosin regulatory light chains, contraction of the afferent arteriole may be regulated by a mechanism normally associated with the much more rapidly contracting cardiac and skeletal muscles, which involves Ca2+ binding to TnC, leading to alleviation of inhibition of the actomyosin MgATPase by TnI and tropomyosin and rapid contraction of the vessel.Support or Funding InformationSupported by the Canadian Institutes of Health ResearchThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.