Effects And Mechanisms Of PH On The Vascular Tone In Rats Isolated Thoracic Aorta Rings

Objective:To observe the effects and the possible mechanisms of different pH on the resting tone and the pre-contracted by NE (norepinephrine) or KCl (potassium chloride) or U46619in rats isolated thoracic aorta rings. To observe the effects of different pH on the diastolic by SNP or DZP in rats isolated thoracic aorta rings.Methods:The method of isolated vascular tension record system was as followed. The experiment was divided into three parts.Part one, effects and mechanisms of pH on the resting tone in rats isolated thoracic aorta rings.(1) Effects of different pH on the resting tone in isolated thoracic rings from adult rats were observed.(2) The vascular reactivity experiments of pH=9.5on the contraction in the thoracic aortic rings were performed in free-Ca2+PSS and CaCl22.5mmol/L, in the presence or absence of calcium channel inhibitor verapamil (VEP,10-5mol/L), Na-/Ca2+exchange inhibitor (KB-R7943,10-6mol/L) and Na+/H+exchange inhibitor amiloride (AM,10-4mol/L).Part two, effects and mechanisms of different pH on the contractions induced by NE or KCl or U46619in the thoracic aortic rings.(1) Effects of different pH on the contractions induced by NE (10-6mol/L) or KCl (60mmol/L) or U46619(10-7mol/L) in the thoracic aortic rings with intact endothelium or denuded endothelium were observed.(2) The effects of various drugs include NG-nitro-L-arginine methyl ester (L-NAME,10-4mol/L), indomethacin (Indo,10-5mol/L) and tetraethyl-ammonium (TEA,10-2mol/L),4-aminopyridine (4-AP,10-3mol/L), glibenclamide (Gli,10-5mol/L), barium chloride(BaCl2,10-3mol/L)were also studied in the rings.Part three, effects of different pH on the diastolic by SNP (10-9～10-5mol/L) or DZP (10-7～10-4mol/L) in rats isolated thoracic aorta rings were also observed.Results:The statement was divided into three parts.Part one, effects and mechanisms of pH on the resting tone in rats isolated thoracic aorta rings.(1) The increase of extracellular pH enhanced the resting tone in rats isolated thoracic aorta rings, but decrease had no effect on the resting tone. When extracellular pH values reached8.5,9.0,9.5and10.0, the Emax were (11.79±6.83)％,(30.25±3.57)％,(92.24±5.73)％and(110.85±7.78)％,respec-tively.(2)Both extracellular Ca2-influx and intracellular Ca2+release involved in the contraction in the thoracic aortic rings of pH=9.5,and it related to VEP (P<0.01).The contraction was diminished by KB-R7943and AM(P<0.01),with the Emax of(48.33±5.75)％and(32.12±4.45)％,respectively.Part two,effects and mechanisms of different pH on the contractions induced by NE or KCl or U46619in the thoracic aortic rings.(1)The decrease of extracellular pH diminished the contraction by10-6mol/L NE in rats isolated thoracic aorta rings.When extracellular pH values reached7.0,6.5,6.0,5.5and5.0,the Emax were(100.26±11.56)％,(76.07±9.54)％,(35.04±9.59)％,(21.52±13.86)％and(14.64±8.92)％,respectively.However,the increase of extracellular pH diminished the contraction by NE in rats isolated thoracic aorta rings.When extracellular pH values reached8.0,8.5,9.0,9.5and10.0,the Emax were (107.27±15.68)％,(77.21±12.17)％,(45.58±3.60)％,(27.52±18.88)％and(0.08±0.10)％,respectively.(2)The decrease of extracellular pH enhanced first and then diminished the contraction by60mmol/L KCl in rats isolated thoracic aorta rings. When extracellular pH values reached7.0,6.5,6.0,5.5,5.0and4.5,the Emax were (113.35±5.04)％,(106.55±5.71)％,(95.38±7.85)％,(66.84±11.86)％,(57.36±4.31)％and(17.33±1.51)％, respectively. However,the increase of extracellular pH enhanced the contraction by KCl in rats isolated thoracic aorta rings. When extracellular pH values reached8.0,8.5,9.0,9.5and10.0,the Emax were (111.73±8.27)％,(112.29±6.29)％,(110.44±5.89)％,(121.15±16.31)％and (3.79±4.40)％,respectively.(3)The decrease of extracellular pH diminished the contraction by10-7mol/L U46619in rats isolated thoracic aorta rings.When extracellular pH values reached7.0,6.5,6.0,5.5and5.0,the Emax were (95.44±3.77)％,(83.38±7.57)％,(65.88±9.54)％,(43.97±3.92)％and(22.48±2.25)％,respectively.However,the increase of extracellular pH diminished the contraction by U46619in rats isolated thoracic aorta rings.When extracellular pH reached8.0,8.5,9.0,9.5and10.0,the Emax were(100.26±2.20)％,(88.44±1.86)％,(71.30±5.34)％,(39.74±3.65)％and(18.53±2.17)％,respectlively.(4) Both pH=6.5and pH=8.5significantly diminished the contraction by10-6mol/L NE in rats isolated thoracic aorta rings,and the effects was restrained by TEA and BaCl2(P<0.01),but had nothing to do with L-NAME,Indo,4-AP and Gli. Part three, effects of different pH on the diastolic by SNP or DZP in rats isolated thoracic aorta rings.(1) Both SNP (10-9～1005mol/L) and DZP (10-7～10-4mol/L) had no effect on the resting tone in different extracellular pH (P>0.05). Both pH=6.5and pH=8.5had no effect on the resting tone, compared with the extracellular pH=7.4(P>0.05).(2) Effects of different pH on the diastolic by SNP(10-9～10-5mol/L) or DZP(10-7～10-4mol/L) induced by NE (10-6mol/L) or KCl (60mmol/L) or U46619(10-7mol/L) in rats isolated thoracic aorta rings were different. Both pH=6.5and pH=8.5significantly enhanced the diastolic in rats isolated thoracic aorta rings, compared with the extracellular pH=7.4(P<0.01).Conclusion:(1) In alkaline conditions, the increase of extracellular pH significantly enhance the resting tone in rats isolated thoracic aorta rings via extracellular Ca2+influx and intracellular Ca2+release. Both Na+/Ca2+exchanger and Na+/H+exchanger are involved in the contraction in the thoracic aortic rings at pH=9.5.(2) Both acidosis and alkalosis significantly diminish the contraction by10-6mol/L NE in rats isolated thoracic aorta rings, and the effects may be related to Kca and Kir, but have nothing to do with endothelium-dependent mechanisms.(3) Both SNP and DZP have no effect on the resting tone in different extracellular pH.(4) Both extracellular acidosis and alkalosis significantly enhance the diastolic in rats isolated thoracic aorta rings.