Modulation by protease-activated receptors of the rat duodenal motility in vitro: possible mechanisms underlying the evoked contraction and relaxation.
1 The present study examined effects of agonist enzymes and receptor-activating peptides for protease-activated receptors (PARs) on duodenal motility in the rat, and also investigated possible mechanisms underlying the evoked responses. 2 Thrombin at 0.03-0.1 microM and the PAR-1-activating peptide SFLLR-NH2 at 3-100 microM or TFLLR-NH2 at 10-50 microM produced a dual action, relaxation followed by contraction of the duodenal longitudinal muscle. The PAR-2-activating peptide SLIGRL-NH2 at 10-100 microM elicited only small contraction. Trypsin at 0.08 microM induced small contraction, or relaxation followed by contraction, depending on preparations. The PAR-4-activating peptide GYPGKF-NH2 at 1000 microM exhibited no effect. 3 The contractile responses of the duodenal strips to TFLLR-NH2 and to SLIGRL-NH2 were partially attenuated by the L-type calcium channel blocker nifedipine (1 microM), the protein kinase C inhibitor GF109203X (1 microM) and the tyrosine kinase inhibitor genistein (15 microM), but were resistant to indomethacin (3 microM) and tetrodotoxin (1-10 microM). 4 The relaxation of the preparations exerted by TFLLR-NH2 was unaffected by indomethacin (3 microM), propranolol (5 microM), NG-nitro-L-arginine methyl ester (100 microM) and tetrodotoxin (1-10 microM). This relaxation was resistant to either GF109203X (1 microM) or genistein (15 microM), but was, remarkably, attenuated by combined application of these two kinase inhibitors. 5 Apamin (0.1 microM), an inhibitor of calcium-activated, small-conductance potassium channels, but not charybdotoxin (0.1 microM), completely abolished the PAR-1-mediated duodenal relaxation, and significantly enhanced the PAR-1-mediated contraction. 6 These findings demonstrate that PAR-1 plays a dual role, suppression and facilitation of smooth muscle motility in the rat duodenum, while PAR-2 plays a minor excitatory role in the muscle, and that PAR-4 is not involved in the duodenal tension modulation. The results also suggest that the contractile responses to PAR-1 and PAR-2 activation are mediated, in part, by activation of L-type calcium channels, protein kinase C and tyrosine kinase, and that the relaxation response to PAR-1 activation occurs via activation of apamin-sensitive, but charybdotoxin-insensitive, potassium channels, in which both protein kinase C and tyrosine kinase might be involved synergistically.
Kawabata
A
A
Department of Pathophysiology & Therapeutics, Faculty of Pharmaceutical Sciences, Kinki University, 3-4-1 Kowakae, Higashi-Osaka 577-8502, Japan.
Kuroda
R
R
Nishikawa
H
H
Kawai
K
K
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects; D004386:Duodenum / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005769:Gastrointestinal Motility / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018179:Receptors, Thrombin / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D009842:Oligopeptides; D018179:Receptors, Thrombin; D013779:Tetrodotoxin; D011433:Propranolol; D014357:Trypsin; D013917:Thrombin; D019331:NG-Nitroarginine Methyl Ester