Erection(tumescence) is a complex neurophysiologic event that leads to relaxation of the smooth muscle cells in the corpus cavernosum penis which allows filling of blood into the cavernous spaces causing an increase in the size and rigidity of the penis. Flaccidity (detumescence) is initiated and maintained by contraction of the corpus cavernosum smooth muscle (CCSM) cells. The CCSM is unique since it remains in the contracted state most of the time. It is not know whether the Ca2+-calmodulin-MLCK pathway or other then filament- mediated regulation (via the actin-binding protein caldesmon) plays a role in keeping these cells in the contracted state, for the penis to remain flaccid. A third possibility is that the myosin isoforms in CCSM play a role in determining the velocity of force generation and the tonicity. A recent study conducted by this investigator showed that the aortic smooth muscle, which is considered tonic, contains one type of myosin isoform whereas the smooth muscle cells in small muscular arteries contain a different myosin isoform. The latter isoform is encoded by a myosin heavy chain mRNA that is alternatively spliced to insert a 21-nucleotide sequence that encodes a region near the ATP-binding site on the myosin head. This insert encodes a 7-amino acid peptide, and the resulting myosin isoform has a two-fold increase in the actin-activated myosin ATPase activity and an associated increase in shortening velocity (Vmax). Similar studies conducted on CCSM in our lab show that the CCSM contains both inserted (as in small muscular arteries and all visceral smooth muscles which show phasic characteristics) and non-inserted (as in aortic smooth muscle which is tonic) myosin heavy chain isoforms. Specially, using CCSM from normal rabbits, normal humans, and patients with erectile dysfunctions, we will address the following questions: (1) Are the differences in the contractile characteristics of CCSM compared to smooth muscle from other sources due to a difference in the composition of smooth muscle myosin isoforms that are produced by alternative splicing of the myosin pre-mRNA at the 3' end (resulting in SM1 and SM2) or the 5' end (resulting in inserted myosin)? (2) What role does myosin light chain phosphorylation play in erectile function and do CCSM cells have higher kinase or lower phosphatase activity compared to other smooth muscle cells (e.g. bladder smooth muscle)? (3) What is the level of expression of myosin light chain kinase and caldesmon in the CCSM and is it altered in patients with erectile dysfunction? Thus, the results from experiments proposed in this application will provide the molecular mechanisms for the regulation of CCSM contraction and delineate specific steps in the pathways for cross-bridge cycling and contractility of smooth muscle cells in the normal corporus cavernosum penis. It will also provide and explanation for changes in contractility of smooth muscle cells seen in patients with erectile dysfunction.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK055529-03
Application #
6177434
Study Section
Special Emphasis Panel (ZRG4-UROL (01))
Program Officer
Rankin, Tracy L
Project Start
1998-09-29
Project End
2003-06-30
Budget Start
2000-07-01
Budget End
2001-06-30
Support Year
3
Fiscal Year
2000
Total Cost
$159,500
Indirect Cost
Name
University of Pennsylvania
Department
Surgery
Type
Schools of Medicine
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
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Chang, Shaohua; Hypolite, Joseph A; Velez, Marielena et al. (2004) Downregulation of cGMP-dependent protein kinase-1 activity in the corpus cavernosum smooth muscle of diabetic rabbits. Am J Physiol Regul Integr Comp Physiol 287:R950-60
Chang, S; Hypolite, J A; Changolkar, A et al. (2003) Increased contractility of diabetic rabbit corpora smooth muscle in response to endothelin is mediated via Rho-kinase beta. Int J Impot Res 15:53-62
Chang, Shaohua; Hypolite, Joseph A; Zderic, Stephen A et al. (2002) Enhanced force generation by corpus cavernosum smooth muscle in rabbits with partial bladder outlet obstruction. J Urol 167:2636-44
Zheng, Yongmu; Weber, Wilfried T; Wang, Shuqin et al. (2002) Generation of a cell line with smooth muscle phenotype from hypertrophied urinary bladder. Am J Physiol Cell Physiol 283:C373-82