title: Photosensitization of oesophageal smooth muscle by 3-NO2-1, 4-dihydropyridines: evidence for two cyclic GMP-dependent effector pathways.
abstract: 1. Photoactivated mechanical responses that resulted from exposure to 3-NO2-1,4-dihydropyridines (3-NO2-DHP5) or NO-donors were examined in rat isolated oesophageal smooth muscle with a view to determining the role of calcium and cyclic GMP. 2. Isometric contractile force was recorded in preparations bathed in normal Tyrode or 110 mM K(+)-depolarizing solution. Exposure to (+)-PN 202791, (+/-)-Bay K 8644 and (-)-PN 2020791 or the photodegradable NO-donors, sodium nitroprusside (SNP), streptozotocin (STZ) and sodium nitrite photosensitized precontracted tunica muscularis mucosae preparations in a concentration-dependent fashion. Photosensitizing potency followed the order: (+/-)-PN 202791 > (+/-)-Bay K 8644 > (-)-PN 202791 > SNP > STZ > NaNO2. 3. A low amplitude, slow photorelaxation (slope: 1 mg s-1) was obtained with the L-channel antagonists (-)-PN 202791 and (+)-Bay K 4407. Photosensitization by the agonist enantiomers (+)-PN 202 791 and (-)-Bay K 5407, as well as racemic Bay K 8644, was mimicked by NO donors and showed at least three different components, consisting of (i) a fast relaxation (slope: 140 mg s-1), (ii) a fast "off-contraction', and (iii) a delayed slow relaxation. The fast components, but not the delayed slow relaxation, were abolished by blockade of L-type voltage-operated calcium channels, chelation of extracellular calcium and skinning of the plasmalemma, suggesting their mediation by a process linked to calcium entry through L-channels. 4. Both cyclopiazonic acid (3-30 microM) and ryanodine (30 microM) inhibited the fast response. This inhibition was accelerated in the presence of extracellular calcium and resembled that seen in tissues exposed to the calcium ionophore A 23187 (1 microM). In calcium depleted tissues, cyclopiazonic acid (3 microM) prevented restoration of the cis-dioxolane-induced contraction following re-exposure to a calcium containing high K+ buffer, but failed to inhibit the photoresponse. 5. Both the fast and slow relaxations were potentiated by zaprinast (10 microM) and inhibited by LY B3583 (10 microM). However, in calcium-depleted, calyculin A-precontracted preparations only the slow relaxation was evident. 6. The present results support the conclusion that: (i) functional L-channels are required for the expression of the fast components of the 3-NO2-DHP- or NO-donor-induced photoresponse, (ii) NO photorelease followed by activation of soluble guanylyl cyclase is responsible for the photosensitizing activity of 3-NO2-DHPs and (iii) regulation of the contractile proteins via cyclic GMP-dependent phosphorylation may underlie the slow relaxation.
authors.affiliation: Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Martin-Caraballo
authors.forename: C R
authors.initials: CR
authors.lastname: Triggle
authors.forename: D
authors.initials: D
authors.lastname: Bieger
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004947:Esophagus / Q000187:drug effects; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008387:Marine Toxins; D009130:Muscle, Smooth / Q000187:drug effects*; D009539:Nicotinic Acids / Q000494:pharmacology*; D009569:Nitric Oxide / Q000819:agonists*; D010069:Oxadiazoles / Q000494:pharmacology*; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011688:Purinones / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012433:Ryanodine / Q000494:pharmacology
chemical_list: D000634:Aminoquinolines; D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D002614:Chelating Agents; D007211:Indoles; D008387:Marine Toxins; D009539:Nicotinic Acids; D010069:Oxadiazoles; D010080:Oxazoles; D017319:Photosensitizing Agents; D011688:Purinones; C049834:PN 202-791; D012433:Ryanodine; D009569:Nitric Oxide; D004533:Egtazic Acid; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C059041:calyculin A; C041715:6-anilino-5,8-quinolinedione; D010749:Phosphoprotein Phosphatases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D006162:Guanylate Cyclase; D000252:Calcium-Transporting ATPases; C011145:zaprinast; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; C000543:cyclopiazonic acid