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Pkd2^+/– Vascular Smooth Muscles Develop Exaggerated Vasocontraction in Response to Phenylephrine Stimulation

Qi Qian^*,, Larry W. Hunter, Hui Du^*, Qun Ren^*, Young Han and Gary C. Sieck

^* Division of Nephrology and Hypertension, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota

Address correspondence to: Dr. Qi Qian, Department of Medicine and Physiology, Eisenberg S-24, Nephrology, Mayo Clinic College of Medicine, 200 First Street, SW, Rochester, MN 55905. Phone: 507-266-7083; Fax: 507-266-9315; E-mail: qian.qi{at}mayo.edu

Received for publication May 19, 2006. Accepted for publication November 13, 2006.

Vascular complications are the leading cause of morbidity and mortality in autosomal dominant polycystic kidney disease. Although evidence suggests an abnormal vascular reactivity, contractile function in Pkd mutant vessels has not been studied previously. Contractile response to phenylephrine (PE; 10^–10 to 10^–4M), an 1-adrenergic receptor agonist, was examined. De-endothelialized Pkd2^+/– aortic rings generated a higher maximum force (F_max) than that in wild-type (wt; 5.78 ± 0.73 versus 2.69 ± 0.43 mN; P < 0.001) and a significant left shift in PE dosage-response curve. On simultaneous recordings, Pkd2^+/– aortic helical strips also responded to PE with a greater F_max but a lesser [Ca²⁺]_i rise, resulting in a greatly enhanced force/Ca²⁺ ratio than that in wt. At F_max, a higher elevation in the phosphorylated regulatory myosin light chain was observed in Pkd2^+/– strips. Ca²⁺-dependent calmodulin/myosin light-chain kinase–mediated contraction was examined by direct Ca²⁺ (pCa8-5) stimulation to -escin permeabilized aortic strips; the pCa-force curve in Pkd2^+/– strips was not shifted, thereby indicating that PE induced dosage-response alteration that resulted from Ca²⁺-independent mechanisms. Quantitative analyses of contractile proteins demonstrated elevated expressions in smooth muscle -actin and myosin heavy chain in Pkd2^+/– arteries, changes that likely contribute to the higher F_max. Similar to those in aortas, de-endothelialized Pkd2^+/– resistance (fourth-order mesenteric) arteries responded to PE with a stronger contraction but a lesser [Ca²⁺]_i rise than in wt. Taken together, the arterial vasculature in Pkd2^+/– mice exhibits an exaggerated contractile response and increased sensitivity to PE. An enhanced Ca²⁺-independent force generation and elevated contractile protein expression likely contribute to these abnormalities.

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Copyright © 2008 by the American Society of Nephrology. Online ISSN: 1533-3450 Print ISSN: 1046-6673