KMUP-1 relaxes rabbit corpus cavernosum smooth muscle in vitro and in vivo: involvement of cyclic GMP and K(+) channels

Abstract

1. In isolated endothelium-intact or denuded rabbit corpus cavernosum preconstricted with phenylephrine, KMUP-1 (0.001 - 10 microM) caused a concentration-dependent relaxation. 2. This relaxation of KMUP-1 was attenuated by endothelium removed, high K(+) and pretreatments with a soluble guanylyl cyclase (sGC) inhibitor ODQ (1 microM), a NOS inhibitor L-NAME (100 microM), a K(+) channel blocker TEA (10 mM), a K(ATP) channel blocker glibenclamide (1 microM), a voltage-dependent K(+) channel blocker 4-AP (100 microM) and Ca(2+)-dependent K(+) channel blockers apamin (1 microM) and charybdotoxin (ChTX, 0.1 microM). 3. The relaxant responses of KMUP-1 (0.01, 0.05, 0.1 microM) together with a PDE inhibitor IBMX (0.5 microM) had additive actions on rabbit corpus cavernosum smooth muscle (CCSM). 4. KMUP-1 (0.01 - 10 microM) induced increase of intracellular cyclic GMP level in the primary cell culture of rabbit CCSM. This increase in cyclic GMP content was abolished in the presence of ODQ (10 microM). 5. Both KMUP-1 and sildenafil at 0.2, 0.4, 0.6 mg kg(-1) caused increases of intracavernous pressure (ICP) and duration of tumescene (DT) in a dose-dependent manner. These in vivo activities of ICP for sildenafil and KMUP-1 are consistent with those of in vitro effects of cyclic GMP. 6. KMUP-1 has the following merits: (1) inhibition of PDE or cyclic GMP breakdown, (2) stimulation of NO/sGC/cyclic GMP pathway, and (3) subsequent stimulation of K(+) channels, in rabbit CCSM. We suggest that these merits play prominent roles in KMUP-1-induced CCSM relaxation-associated increases of ICP and penile erection.

Figure 1

Chemical structures of KMUP-1 and sildenafil.

Figure 2

Effects of KMUP-1 on phenylephrine (10 μM)-precontracted rabbit corpus cavernosum in the endothelium-denuded EC (−) and endothelium-intact EC (+) corporeal smooth muscle strips. ^*P<0.05, n=12 as compared with the KMUP-1 (two way repeated measures ANOVA followed by Student-Newman-Keuls test).

Figure 3

Effects of KMUP-1 on the rabbit corpus cavernosum, precontracted with phenylephrine (10 μM) and 60 mM KCl, respectively. ^*P<0.05, ^**P<0.01, ^***P<0.001, n=12 as compared with the KMUP-1 (two way repeated measures ANOVA followed by Student-Newman-Keuls test).

Figure 4

Effects of KMUP-1 (A) and Sildenafil (B) on phenylephrine (10 μM)-precontracted rabbit corpus cavernosum in the absence and presence of potassium channel blockers. ^*P<0.05, n=12 as compared with the KMUP-1 (two way repeated measures ANOVA followed by Student-Newman-Keuls test).

Figure 5

Effects of KMUP-1 (A) and Sildenafil (B) on phenylephrine (10 μM)-precontracted rabbit corpus cavernosum in the absence and presence of L-NAME (100 μM), ODQ (1 μM). ^*P<0.05, n=12 as compared with the control, respectively (two way repeated measures ANOVA followed by Student-Newman-Keuls test).

Figure 6

Additive effects of KMUP-1 (0.01, 0.05, 0.1 μM) and IBMX (0.5 μM) on phenylephrine (10 μM)-precontracted rabbit carvernosal strips. Each value represents the mean±s.e., ^*P<0.05, n=8 as compared with the control value. (ANOVA followed by Dunnett's test). Control: solvent control.

Figure 7

Effects of KMUP-1 (0.01, 0.1, 1, 10 μM) and sildenafil (0.01, 0.1, 1, 10 μM) on cyclic GMP levels in rabbit corpus cavernosum smooth muscle cells. Each value represents the mean±s.e. from three independent experiments. ^*P<0.05 as compared with the control (ANOVA followed by Dunnett's test). CTL: solvent control.

Figure 8

Effects of KMUP-1 (10 μM) on cyclic GMP levels in rabbit corpus cavernosal smooth muscle cells and in the absence or presence of ODQ (10 μM) and methylene blue (100 μM). Each value represents the mean±s.e. from three independent experiments. ^**P<0.01 as compared with the KMUP-1 (ANOVA followed by Dunnett's test).

Figure 9

Hypothetical action mechanisms of KMUP-1 in corpus cavernosum smooth muscle.