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NEUROREGULATION AND MOTILITY

Mechanism of internal anal sphincter relaxation by CORM-1, authentic CO, and NANC nerve stimulation

Division of Gastroenterology and Hepatology, Department of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107

Submitted 11 February 2004 ; accepted in final form 30 March 2004

The present studies compared the effects of CO-releasing molecule (CORM-1), authentic CO, and nonadrenergic noncholinergic (NANC) nerve stimulation in the internal anal sphincter (IAS). Functional in vitro experiments and Western blot studies were conducted in rat IAS smooth muscle. We examined the effects of CORM-1 (50–600 µM) and authentic CO (5–100 µM) and NANC nerve stimulation by electrical field stimulation (EFS; 0.5–20 Hz, 0.5-ms pulse, 12 V, 4-s train). The experiments were repeated after preincubation of the tissues with the neurotoxin TTX, the guanylate cyclase inhibitor 1H-(1,2,4)oxadiazolo-(4,3-a)quinoxalin-1-one (ODQ), the selective heme oxygenase (HO) inhibitor tin protoporphyrin IX (SnPP-IX), the nitric oxide synthase inhibitor N-nitro-L-arginine (L-NNA), and SnPP-IX + L-NNA. We also investigated the effects of the HO substrate hematin (100 µM). CORM-1, as well as CO, produced concentration-dependent IAS relaxation, whereas hematin had no effect. TTX abolished and L-NNA significantly blocked IAS relaxation by EFS without any effect on CORM-1 and CO. ODQ blocked IAS relaxation by CORM-1, authentic CO, and EFS. SnPP-IX had no significant effect on IAS relaxation by CORM-1, CO, or EFS. The presence of neuronal nitric oxide synthase, HO-1, and HO-2 in IAS smooth muscle was confirmed by Western blot studies. CORM-1 and CO, as well as NANC nerve stimulation, produced IAS relaxation via guanylate cyclase/cGMP-dependent protein kinase activation. The advent of CORM-1 with potent effects in the IAS has significant implications in anorectal motility disorders with regard to pathophysiology and therapeutic potentials.

heme oxygenase; inhibitory neurotransmitter; nitric oxide synthase; guanylate cyclase; smooth muscle

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