In vitro and in vivo relaxation of corpus cavernosum smooth muscle by the selective myosin II inhibitor, blebbistatin

Introduction Blebbistatin (BLEB) is a small cell permeable molecule originally reported as a selective inhibitor of myosin II isoforms expressed by striated muscle and non-muscle cells (IC 50 = 0.5–5 µM) with poor inhibition of turkey gizzard smooth muscle (SM) myosin II (IC 50 ∼80 µM). However, recently it was found that BLEB can potently inhibit mammalian arterial SM (IC 50 ∼5 µM). Aim To investigate the effect of BLEB on corpus cavernosum SM (CCSM) tone and erectile function (EF). Methods CC tissue obtained from penile implant patients along with CC, aorta and bladder from adult male rats were used for BLEB organ bath studies. Intracavernosal BLEB was administered to rats and EF was assessed via intracavernous pressure (ICP). Main Outcome Measures Effects of BLEB on agonist-induced CCSM, aorta and bladder contraction in vitro and ICP in vivo. Results BLEB completely relaxed human CCSM pre-contracted with phenylephrine (PE) in a dose-dependent manner decreasing tension by 76.5% at 10 µM. BLEB pre-incubation attenuated PE-induced contraction of human CC by ∼85%. Human CC strips pre-contracted with endothelin-1 or KCl were almost completely relaxed by BLEB. Rat CCSM pre-contracted with PE showed BLEB relaxation comparable to human CCSM. BLEB inhibition was similar for rat aorta but slower for bladder. Both maximal ICP and ICP/mean arterial pressure were dose-dependently increased by BLEB intracavernous injections with full erection at 1 micromole. Conclusion Our novel data reveals that BLEB nearly completely relaxes rat and human CCSM pre-contracted with a variety of potent agonists and exhibits tissue selectivity. Coupled with our in vivo data in which nanomole doses of BLEB significantly increase ICP, our data substantiates an important role for the SM contractile apparatus in the molecular mechanism for EF and suggests the possibility of BLEB binding at myosin II as a therapeutic treatment for ED by targeting SM contractile pathways. Zhang X, Aydin M, Kuppam D, Melman A, and DiSanto ME. In vitro and in vivo relaxation of corpus cavernosum smooth muscle by the selective myosin II inhibitor, blebbistatin. J Sex Med 2009;6:2661–2671.