Mo1650 Purinergic Inhibitory Neuromuscular Transmission in Human Jejunum and Guinea Pig Colon

Abstract

The soluble guanylyl cyclase is expressed in guinea-pig gallbladder smooth muscle and agents that stimulate this enzyme activity cause gallbladder relaxation. The compound 5Cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine (BAY 41-2272) is a potent nitric oxide (NO)-independent soluble guanylyl cyclase stimulator, but little is known about its effects in gallbladder smooth muscle. This study investigated the mechanisms underlying the relaxations of guinea-pig gallbladder smooth muscle induced by BAY 41-2272. Gallbladder strips were mounted in 20-ml organ baths for isometric force recording. BAY 41-2272 concentration-dependently relaxed histamine-precontracted gallbladder strips. Prior incubation with the NO synthesis inhibitor L-NAME (0.1 mM) or the soluble guanylyl cyclase inhibitor ODQ (10 μM) caused significant rightward shifts in the concentration-response curves to BAY 41-2272. NO-donor, sodium nitroprusside caused concentration-dependent relaxations, which were greatly potentiated by BAY 41-2272 and almost completely inhibited by ODQ. To evaluate the effect of K+ channels, the relaxant responses of gallbladder muscle to Bay 41-2272 remained unchanged selective K+ channel inhibitor such as glibenclamide (10 μM), 4-aminopyridine (1 mM) or the co-incubation of charybdotoxin (0.1 μM) with apamin (1 μM). To evaluate the participation of prostanoids and cAMP pathway, the cyclooxygenase inhibitor indomethacin (10 μM) and selective phosphodiesterase type 4 inhibitor rolipram (1 μM) failed to significantly affect the BAY 41-2272-induced gallbladder relaxations. BAY 41-2272 shifted to the right the gallbladder contractile responses to either histamine (0.0001-10 μM). BAY 41-2272 (10 μM) also caused a marked rightward shift and decreased the maximal contractile responses to extracellular CaCl2. The effects of an inhibitor of the PKA, Rp-8CPT-cAMPS (10 μM), or the PKG, Rp8-pCPT-cGMPS (10 μM) on relaxation induced by the cumulative adminstration of BAY 41-2272 were studied in precontracted with 1 μM histamine. The relaxing effect of BAY 41-2272 were significantly attenuated by Rp-8-pCPT-cGMPS, but not by Rp-8CPT-cAMPS. These results indicate that BAY 41-2272 causes cGMP-dependent guinea-pig gallbladder smooth muscle relaxations in a synergistic fashion with NO. BAY 41-2272 has also an additional mechanism independently of soluble guanylyl cyclase activation possibly involving Ca2+ entry blockade.