The Mechanisms Underlying Rat Isolated Coronary Artery Vasoconstriction Induced By Acidosis

Objective:To study the effects of acidosis?pHex6.8?on the resting tone of rat isolated coronary artery?CA?,and to explore the underlying mechanisms by inhibitor study.To study the possible involvement of acid-base transporters in the vasoconstriction induced by pHex6.8 in rat isolated CA by observing the effects of inhibitors of Na+-H+ exchanger subtype 1?NHE-1?and Na+-HCO3-cotransporter?NBC?on the vasoconstriction force.To clarify the relationship of chloride transport across the membrane with the constriction induced by pHex6.8 in rat isolated CA by applying chloride channel blockers?NPPB and NFA?and using anionic substitution method.To investigate the role of Rho kinase?ROCK?,protein kinase C?PKC?and extracellular signal-regulated kinase?ERK?in the vasoconstriction by using their respective pharmacological inhibitors.Methods:1.When the male SD rats?230 260 g?were killed by decapitation,the hearts were quickly taken out,and transferred into chilled?4??Physiological saline solution?PSS?that was maintained at pH 7.40 with the gas mixture of 95% O₂+5% CO₂.The rat CA rings were separated under the dissecting microscope,cut into 2 mm-long rings,and then mounted on a wire myograph?Multi Myograph System-610 M,DMT?.The tone of rat isolated CA rings was recorded by PowerLab and DMT systems.2.The rings were incubated with NHE-1 inhibitor HOE-642?30 ?mol/L?and NBC inhibitor S0859?100 ?mol/L?respectively to observe their effects on rat isolated CA constriction induced by pHex6.8.3.The rings were incubated with chloride channel blockers NPPB?10,30,100?mol/L?and NFA?10,30,100 ?mol/L?respectively to observe their effects on rat isolated CA constriction induced by pHex6.8.The rings were incubated with chloride channel blockers NPPB?10,30,100,300 ?mol/L?and NFA?10,30,100,300 ?mol/L?respectively to observe their effects on rat isolated CA constriction induced by KCl?60mmol/L?.Similarly,the effects of NPPB?100 ?mol/L?and NFA?100 ?mol/L?on rat isolated CA constriction induced by TXA2 analogues U46619?1 ?mol/L?were observed respectively.The myogenic effects of pHex6.8,KCl?60 mmol/L?and U46619?1 ?mol/L?were observed in PSS deprived of Cl-by replacing the extracellular NaCl with equimolar sodium asparate.4.The rings were incubated with ROCK inhibitor Y-27632?3 ?mol/L?,PKC inhibitor G? 6983?1 ?mol/L?and ERK inhibitor PD98059?10 ?mol/L?respectively to observe their effects on rat isolated CA constriction induced by pHex6.8.Results:1.pHex6.8 constricted rat isolated CA,the maximum constriction was?3.90 ± 0.95?mN,and accounted for?105.07 ± 10.65?% of the maximal constriction induced by KCl?60 mmol/L?.2.HOE-642?30 ?mol/L?and S0859?100 ?mol/L?both inhibited the pHex6.8-induced constriction,and the inhibitory percentages were?18.46 ± 5.29?%?P <0.01?and?14.90 ± 3.24?%?P < 0.01?,respectively.3.NPPB?10,30,100 ?mol/L?and NFA?10,30,100 ?mol/L?both inhibited the pHex6.8-induced constriction in a concentration-dependent manner,the maximal inhibitory percentages were?66.61 ± 7.07?%?P < 0.01?and?64.48 ± 11.68?%?P < 0.01?,respectively.NPPB?10,30,100,300 ?mol/L?and NFA?10,30,100,300 ?mol/L?both inhibited the KCl-induced constriction in a concentration-dependent fashion,the maximal inhibitory percentages were?83.51 ± 3.13?%?P < 0.01?and?52.37 ± 12.31?%?P < 0.01?,respectively.NPPB?100 ?mol/L?and NFA?100 ?mol/L?both inhibited the U46619-induced constriction,the maximal inhibitory percentages were?44.04 ± 9.68?%?P < 0.01?and?46.23 ± 5.24?%?P < 0.01?,respectively.After replacing the extracellularNaCl with equimolar sodium asparate,it almost completely inhibited the pHex6.8-induced constriction?P < 0.01?,but had no significant effects on the KCl-induced constriction and U46619-induced constriction?P > 0.05?.4.ROCK inhibitor Y-27632?3 ?mol/L?,PKC inhibitor G? 6983?1?mol/L?and ERK inhibitor PD98059?10 ?mol/L?all inhibited the pHex6.8-induced constriction,and the inhibitory percentages were?29.37 ± 13.44?%?P < 0.01?,?29.84 ± 10.58?%?P < 0.01?and?23.14 ± 9.47?%?P < 0.01?,respectively.Conclusion:1.Activations of both NHE-1 and NBC may be involved in acidosis-induced rat coronary constriction.2.Enhanced chloride transport across the membrane and chloride channels might play important role in acidosis-induced rat coronary constriction.3.Activations of ROCK,PKC and ERK may be involved in acidosis-induced rat coronary constriction.