Submitted on February 15, 2006
Accepted on May 1, 2006
Regional differences in myosin heavy chain isoform expression and maximal shortening velocity of the rat vaginal wall smooth muscle
Maureen Basha1, Shaohua Chang1, Elaine M. Smolock2, Robert S. Moreland3, Alan J. Wein1, and Samuel Chacko4*
1 Division of Urology, University of Pennsylvania, Philadelphia, Pennsylvania, United States
2 Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States
3 Drexel University College of Medicine, Philadelphia, Pennsylvania, United States
4 Division of Urology, University of Pennsylvania, Philadelphia, Pennsylvania, United States; Department of Pathobiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States
* To whom correspondence should be addressed. E-mail: chackosk{at}mail.med.upenn.edu.
Contractility of the proximal and distal vaginal wall smooth muscle may play distinct roles in the female sexual response and pelvic support. The goal of this study was to determine if differences in contractile characteristics of smooth muscle from these regions resides in differences in the expression of isoforms of myosin, the molecular motor for muscle contraction. Adult female Sprague-Dawley rats were sacrificed on the day of estrus and the vagina was dissected into proximal and distal segments. The Vmax at peak force was greater for tissue strips of the proximal vagina compared to that of distal (P<0.01), although, at steady state, the Vmax for the muscle strips from the two regions was not different. Furthermore, at steady state, muscle stress was higher (P<0.001) for distal vaginal strips (n=5). Consistent with the high Vmax for the proximal vaginal strips, RT-PCR results revealed a higher %SM-B (P<0.001) in the proximal vagina. A greater expression of SM-B protein (P<0.001) was also detected by Western blotting (n=4). Interestingly, there was no regional difference noted in SM-1/SM-2 isoforms (n=6). The proximal vagina had a higher expression of myosin heavy chain protein (P<.01) and a greater % of smooth muscle bundles (P<0.001). The results of this study are the first demonstration of a regional heterogeneity in Vmax and myosin isoform distribution in the vagina wall smooth muscle and confirm that the proximal vaginal smooth muscle exhibits phasic contractile characteristics compared to the distal vaginal smooth muscle which is tonic.
