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This Article Full Text Full Text (PDF) All Versions of this Article: 297/5/H1930    most recent 00129.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Smolock, E. M. Articles by Moreland, R. S. PubMed PubMed Citation Articles by Smolock, E. M. Articles by Moreland, R. S.

siRNA-mediated knockdown of h-caldesmon in vascular smooth muscle

Departments of ¹Pharmacology and Physiology and ²Pathology and Laboratory Medicine, Drexel University College of Medicine, and ³Division of Urology, Department of Surgery, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania

Submitted February 6, 2009 ; accepted in final form September 15, 2009

Smooth muscle contraction involves phosphorylation of the regulatory myosin light chain. However, this thick-filament system of regulation cannot account for all aspects of a smooth muscle contraction. An alternate site of contractile regulation may be in the thin-filament-associated proteins, in particular caldesmon. Caldesmon has been proposed to be an inhibitory protein that acts either as a brake to stop any increase in resting or basal tone, or as a modulatory protein during contraction. The goal of this study was to use short interfering RNA technology to decrease the levels of the smooth muscle-specific isoform of caldesmon in intact vascular smooth muscle tissue to determine more carefully what role(s) caldesmon has in smooth muscle regulation. Intact strips of vascular tissue depleted of caldesmon produced significant levels of shortening velocity, indicative of cross-bridge cycling, in the unstimulated tissue and exhibited lower levels of contractile force to histamine. Our results also suggest that caldesmon does not play a role in the cooperative activation of unphosphorylated cross bridges by phosphorylated cross bridges. The velocity of shortening of the constitutively active tissue and the high basal values of myosin light chain phosphorylation suggest that h-caldesmon in vivo acts as a brake against contractions due to basally phosphorylated myosin. It is also possible that phosphorylation of h-caldesmon alone in the resting state may be a mechanism to produce increases in force without stimulation and increases in calcium. Disinhibition of h-caldesmon by phosphorylation would then allow force to be developed by activated myosin in the resting state.

myosin light chain; shortening velocity; cooperativity; carotid artery; cross-bridge cycling