Spectral Properties Of Sulfur Dioxide And Its Derivatives And Its Ion Channel And Signal Transduction Mechanisms Of Vasorelaxation On Isolated Rat Aortic Rings

As we know, sulfur dioxide (SO2) is a common gaseous pollutant. Our previous studies showed that SO2and its derivatives are systemic toxins, which may cause many kinds of toxicological effects not only in respiratory system but also other system of mammals. Epidemiological studies have shown that SO2was correlative with the cardiovascular diseases such as ischemic heart diseases, myocardial ischemia, spontaneous hypertension, and hypoxic pulmonary hypertension. Compared with epidemiological studies, little research has been made on the mechanism of SO2induced cardiovascular diseases. Our recent studies demonstrated that gaseous SO2had a biological role in regulating cardiovascular functions, and SO2could cause relaxation of rat thoracic aortic rings in a concentration-dependent manner. Nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) were considered as gasotransmitters. Recent studies found that SO2was may be the fourth endogenous gaseous transmitter in the cardiovascular system. To the best of our knowledge, few publications tried to show the spectra of SO2and its derivatives. In present study, the absorption spectra of SO2, sodium sulfite (Na2SO3), sodium bisulfite (NaHSO5) and sodium metabisulfite (Na2S2O5, SMB) in aqueous solution were studied. At the same time, the vasodilator effects and its ion channel and signal transduction mechanisms of Na2SO3, Na2S2O5and NaHSO3on isolated rat aortic rings were investigated.In present paper, we investigated the absorption spectra of SO2, sodium sulfite, sodium bisulfite and sodium metabisulfite in aqueous solution. In the meanwhile, the effects of HCl on spectral properties of SO2and its derivatives were also investigated. The results showed that:(1) Sulfur dioxide in water, ethanol, n-butyl-alcohol and glycerol had a characteristic absorption peak at276,277,276and278nm respectively.(2) The absorption value of SO2in water was much smaller than in ethanol, n-butyl-alcohol and glycerol. We attributed the absorbing power of SO2to SO2molecule, rather than hydrated sulfur dioxide.(3) Na2S2O5and NaHS03exhibited a characteristic absorption peak at257nm. Na2SO3solution did not show a characteristic absorption from200to800nm.(4) The absorption of SO2at276nm was strongly enhanced in the presence of HC1, H2SO4, HNO3, H3PO4and HAc but not KC1, MgCl2, NaCl and CaCl2solution. The absorption of SO2strongly enhanced by HCl at276nm was due to H+, instead of the formation of a complex SO2Cl-.(5) NaHSO3, Na2SO3and Na2S2O5also exhibited an absorption at276nm with the addition of HC1, which was enhanced with the increase of HCl concentration.(6) NaHSO3and Na2S2O5solution in presence of H+may be acted as a donor of SO2in biology and other area.To study the biological role of bisulfite on vascular contractility and its underlying cellular and molecular mechanisms, and to explore whether bisulfite can be used as a SO2donor in the biological experiments, the vasorelaxant effects of sodium bisulfite and sodium sulfite on isolated rat thoracic aortic rings were compared; and the signal transduction pathways and the ion channels involved in the vascular effects of bisulfite were investigated. The results showed that:(1) Sodium bisulfite relaxed rat thoracic aortic rings in a concentration-dependent manner (from100to4000μM); however, sodium sulfite at500and1000μM caused vasoconstriction, and only at higher concentrations (from2000to4000μM) it caused vasorelaxation in a concentration-dependent manner.(2) The EC50values of vasorelaxation effects induced by NaHSO3solution with and without200μM HCl were2078±88.57μM and2326±78.56μM, respectively. The vasorelaxation of isolated rat thoracic aortic rings induced by NaHSO3solution with HCl added was stronger than that of NaHSO3solution without HC1.(3) The vasorelaxation caused by the bisulfite at low concentrations (<500μM) was endothelium-dependent, but at high concentrations (>1000μM) it was endothelium-independent.(4) The vasorelaxant effects induced by the high concentrations (2000,4000μM) NaHSO3solution were partially inhibited by nifedipine (an L-type Ca2+channel blocker). But the vasorelaxant effects induced by the low concentration (400μM) NaHSO3solution were not affected by nifedipine.(5) The vasorelaxant effects induced by NaHSO3at low concentration were partially inhibited by TEA (many different types of K+channel inhibitor) or iberiotoxin (BKCa channel inhibitor), but not by glibenclamide (KATP channel inhibitor). The vasorelaxant effects induced by NaHSO3at high concentrations were partially inhibited by TEA or glibenclamide, but not by iberiotoxin.(6) The vasorelaxation induced by NaHSO3at low concentrations was virtually abolished by L-NNA or NS-2028. However, the vasorelaxation induced by NaHSO3at high concentrations was not altered by L-NNA or NS-2028.(7) Indomethacin (an inhibitor of cycloxygenase, one of PGl2-synthetases) or staurosporine (an inhibitor of PKC) or propranolol (an antagonist of P-noradrenoceptor) did not change the vasorelaxation effect of NaHSO3on isolated rat aortic rings.In the present paper, the vasodilator effects of Na2S2O5and roles of Ca2+and K+channels as well as the cGMP pathway on isolated rat aortic rings were studied. The results show that the removal of functional endothelium abolished the relaxation response to Na2S2O5at low concentrations (<400μM), indicating that vasorelaxation was endothelium-dependent. However, Na2S2O5at high concentrations (>500μM) caused vasorelaxation of both endothelium-intact and endothelium-denuded rings, indicating that the vasorelaxation was endothelium-independent. The maximal endothelium-dependent vasorelaxation of Na2S2O5was rather smaller, approximately20%in comparison with those not depending on the presence of the endothelium was more than90%. We also studied the role of L-type calcium channels in Na2S2O5-induced vasorelaxation. The result showed that the vasorelaxant effects of1000μM Na2S2O5on both endothelium-intact and endothelium-denuded rings were partially inhibited by nifedipine. The relaxation effect induced by1000μM Na2S2O5in presence of1μM nifedipine was lower than that in absence of1μM nifedipine, which suggested a possible involvement of L-type Ca2+channels. We investigated the role of indomethacin in the vasorelaxation effect of Na2S2O5. The result showed that the treatment of indomethacin did not affect the vasorelaxation of Na2S2O5at low and high concentrations, which suggested that the vasorelaxant effect of Na2S2O5was not mediated by PGI2. To clarify the potential involvement of K+channels, aortic rings were pre-incubated with10mM TEA,2.5mM4-AP,100nM iberiotoxin,50nM apamin and10μM glibenclamide for20min prior to the application of Na2S2O5, respectively. The results showed that (1) The Na2S2O5-induced vasorelaxation was partially inhibited by TEA that blocked many K+channels in vascular SMCs, including Kca, Kv and KATP channels. Blocker of Kv channel failed to affect the vascular effects of Na2S2O5.(2) Iberiotoxin partially inhibited the50,200μM Na2S2O5-induced vasorelaxation for the endothelium-intact rings, suggesting that BKCa channels might be responsible for the low concentrations Na2S2O5-induced vasorelaxation. The Na2S2O5-induced vasorelaxation was not affected by apamin, suggesting that small-conductance KCa channels might not be responsible for the Na2S2O5-induced vasorelaxation.(3) Glibenclamide partially inhibited the1000μM Na2S2O5-induced vasorelaxation for both endothelium-intact and endothelium-denuded rings, showing that KATP channel might be attributed to the high concentrations Na2S2O5-induced vasorelaxation.(4) The relaxant effect of Na2S2O5was not affected by4-AP. These results suggested that opening of K+channels (BKCa and KATP) might contribute to the vasorelaxant effect of Na2S2O5. To examine whether the Na2S2O5-induced vasorelaxation was mediated by cGMP pathway, we studied the vascular effect of Na2S2O5in the presence of the sGC inhibitors NS-2028and the NO synthase inhibitor L-NNA, respectively. Relaxation induced by low concentrations Na2S2O5was virtually abolished by L-NNA or NS-2028. However, the high concentrations Na2S2O5-induced relaxation was not altered by L-NNA or NS-2028.In summary, these findings led to the conclusions:(1) Spectral properties of sulfur dioxide and its derivatives dissolved in water were different. Sulfur dioxide in water had a characteristic absorption peak at276rm. And the characteristic aborption peak of Na2S2O5and NaHSO3were257nn. Na2SO3solution did not show a characteristic absorption from200to800nm.(2) The vasodilator effects of Na2SO3, Na2S2O5and NaHSO3on isolated rat aortic rings were different. Na2S2O5or NaHSO3caused relaxation of isolated rat thoracic aortic rings in a concentration-dependent manner. However, Na2SO3could cause constriction in low concentration (<2mM) and relaxation in high concentration.(3) The vasorelaxation of Na2S2O5or NaHSO3at low concentrations was endothelium-dependent and mediated by the cGMP pathway and BKca channel, but that at high concentrations was endothelium-independent and mediated by KATP and L-type Ca2+channels. The vasorelaxant effect of Na2S2O5or NaHSO3was disproved the involvement of PKC, PGI2and β-adrenoceptor pathways.(4) Na2S2O5or NaHSO3in presence of H+can be used as a SO2donor for the study of SO2biology.