title: Photodynamic action of aluminium phthalocyanine tetrasulphonate (A1PcS4) on smooth muscle: effects of thiols and a cyclic GMP analogue.
abstract: 1. The smooth muscle system of the guinea-pig taenia caeci has been used in vitro to characterize the photodynamic action of aluminium phthalocyanine tetrasulphonate (A1PcS4) in the presence or absence of the thiol reductants L-cysteine (Cys), N-acetyl-L-cysteine (NAC), DL-dithiothreitol (DTT) or reduced glutathione (GSH). 2. In all photodynamic experiments the muscle was exposed to A1PcS4 (10(-5) M) for 30 min, followed by a 30 min washout period before photon irradiation at 32,000 lux (lambda > 570 nm) for 30 min. Photodynamic contractions were measured relative to the contractile response to carbachol (5 x 10(-5) M) and relaxation responses were determined in muscle precontracted with either carbachol 5 x 10(-5) M or KCl 23.5 mM. 3. Photon-activation of A1PcS4-sensitized smooth muscle evoked a triphasic response: an initial transient contraction and subsequent relaxation followed by a secondary sustained contraction. Cys 10 mM, NAC 10 mM and DTT 5 mM had no effect on the initial photodynamic contraction but significantly decreased the magnitude of the sustained contraction from mean values of 98% to 18%, 95% to 72% and 93% to 6% of the standard carbachol contraction (5 x 10(-5) M), respectively; GSH 10 mM was without significant effect on either the initial or sustained contraction. 4. In the absence of extracellular calcium the A1PcS4-sensitized smooth muscle did not respond to photon activation but re-introduction of calcium after cessation of illumination produced a sustained contraction which was markedly inhibited by Cys 10 mM. 5. In precontracted AlPcS4-treated muscle preparations photon activation produced a triphasic relaxation response, i.e. a rapid relaxation followed by a transient contraction and a secondary more sustained relaxation. The sustained phase of photodynamic relaxation was potentiated significantly by Cys 10 mM,NAC 10 mM, DTT 5 mM and GSH 10 mM, the relaxation being approximately doubled in magnitude from mean values of 34% to 68%, 30% to 73%, 34% to 68%, and 48% to 77%, respectively, relative to the standard carbachol (5 x l0-5 M) response.6. The cyclic GMP analogue, 8-(4-chlorophenylthio)-guanosine-3':5'-cyclic monophosphate (8-PCPTcGMP)(2 x 10-4 M) alone caused a triphasic relaxation response similar to that produced by photon activation of an AIPcS4-sensitized precontracted preparation in the presence of thiol reductants. The pattern of 8-PCPT-cGMP-induced relaxation was similar in muscle precontracted with carbachol 5 x 10-5M or KCI 23.5 mM.7. It is concluded that the rapid generation of reactive intermediates by photon-activation of boundAlPcS4 leads to membrane permeabilization, calcium entry and muscle contraction. These effects may be opposed by a direct stimulatory action of singlet oxygen on guanylate cyclase which is enhanced by the action of thiol reagents and mimicked by the cyclic GMP analogue, 8-PCPT-cGMP.
authors.affiliation: Department of Pharmacology, University of Cambridge.
authors.forename: E K
authors.initials: EK
authors.lastname: Matthews
authors.forename: C
authors.initials: C
authors.lastname: Flaherty
authors.forename: W H
authors.initials: WH
authors.lastname: Smith
mesh_terms: D000818:Animals; D002432:Cecum / Q000187:drug effects; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000096:biosynthesis; D006168:Guinea Pigs; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009942:Organometallic Compounds / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010778:Photochemotherapy; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013438:Sulfhydryl Compounds / Q000494:pharmacology*; D013873:Thionucleotides / Q000494:pharmacology*
chemical_list: D007211:Indoles; D009942:Organometallic Compounds; D010975:Platelet Aggregation Inhibitors; D011838:Radiation-Sensitizing Agents; D013438:Sulfhydryl Compounds; D013873:Thionucleotides; C048577:aluminum tetrasulfophthalocyanine; C055656:8-((4-chlorophenyl)thio)cyclic-3',5'-GMP; D006162:Guanylate Cyclase; D006152:Cyclic GMP