Effects Of Acidosis On Rat Coronary Tone And Related Mechanisms Study

Background:Physiological events or pathophysiological diseases result in the increasing need to energy in critical organs, such as brain and heart. The excessive requirement to energy of the high energy-intensive tissues in the long or short term leads to likely that tricarboxylic acid cycle cannot afford the require of overmuch energy, and that the process of glycolysis is enhanced to increase the output of acidic metabolite, such as pyruvate and lactate. Acidosis induced by the release of acidic metabolite affects the arterial tone of different regions of vascular tree. Ischemia/hypoxia of local tissue in myocardial infarction induces the severe acidosis which produces the harmful injury to the local tissue, such as CA ASMCs and myocardial cells. The present studies indicate that acidosis can induce vasodilation in the CA of rabbit and pig. Conversely, acidosis can induce the increase of arterial tone in rat aorta and pulmonary artery. Controversially, acidosis dilated rat CA to enhance coronary arterial flow. So far it is elusive that acidosis develops the inconsistently vascular function in different species and different regions of the vascular tree. What’s more, the present studies also verify that acidosis jeopardizes myocardium and proper alkalinization of extracellular fluid may be cardioprotective. The above opinions indicate that the recovery of CA reperfusion in myocardial infarction and the therapy of acidosis are likely of importance to recover the injured myocyte. Therefore, it is vital to clarify the effects of acidosis to CA tone, the mechanisms of acidosis-induced CA contraction, and the different vascular functions of acidosis that would contribute to provide the interesting guideline for doctors to remedy the ischemia/hypoxia diseases. Objectives:we established the current study to demonstrate:1. Effects of acidosis on the resting tone of CA and the dose-response curve of CA constriction induced by vasoconstrictors.2. To explore the likely differences among vasoconstrictions induced by acidosis in CA, RIA and MA.3. To observe the effects of acidosis on the current amplitude of LTCC and Kv in CA, RIA and MA owing to they are the vital regulators of vascular function.4. Acidosis rapidly affects SMC pHin that is adjusted by the acid-base transporters in cell membrane. Therefore, it is essential that we focus on the effects of the inhibitors of acid-base transporters on the arterial force, ASMCs [Ca2+]in and pHin.5. To clarify the relationship of among pHin, pHex and CA tone.Research contents and methodsMale Wistar rats weighing200-220g were used. To study the effects of acidosis on CAtone and related mechanisms study.The first section To observe the effect of acidosis on CPF of the isolated heart with Langendorff method. Meanwhile, the direct effect of acidosis on CA diameter was observed by cannulated and pressurized artery in order to remove the effects of heart rate and myocardial contractility.The second section Effects of acidosis on the basic force of CA, RIA and MA and vasoconstriction induced by vasoconstrictors in CA were observed by wire myograph method. The releasing of organelles Ca2+and influx of extracellular Ca2+were focused during pHex6.8-induced contraction in CA. Effects of acid-base transporter inhibitors, such as1μM or3μM Lans,10μM Amil,10μM DIDS, and1μM KB R7943(Na+/Ca2+exchanger inhibitor), simultaneously, on acidosis-induced CA contraction were the focal points.The third section To observe the morphological changes of SMC in CA, RIA and MA during acidosis in order to demonstrate the its direct action on ASMCs. In the whole-cell patch clamp method, we observed the action of changes of pHex and pHin on LTCC of ASMCs and effect of pHex changes on KV. To clarify the effects of pHex on pHin and acid-base transporters during vasoconstriction of CA in acidosis, we observed the likely actions of acid-base transporter inhibitors, such as1μM or3uM Lans,10μM Amil and10μM DIDS, in the process of changes of SMC [Ca2+]in and pHin due to the acidic pHex.Results:1. Acidosis attenuated the LVP and CPF in the isolated Langendorff rat hearts, and narrowed the cannulated CA.2. Acidosis augmented singly the basic force of CA, but there was no effect on the resting tone of RIA and MA. It was logically consistent that acidosis contributed to vasoconstriction triggered by KCl and U46619in CA.3. Vasoconstriction induced by acidosis was mainly dependent on influx of extracellular Ca2+in CA.4. Inhibitors of proton pump and Na+/HCO3-transporter attenuated both pHex6.8-induced vasoconstriction of CA. Especially, the decreasing action of DIDS was stronger than that of Lans. There was no effect of Amil on acidosis-triggered CA contraction. Na+/Ca2+exchanger inhibitors, KB-R7943, slightly weakened the above vasoconstriction.5. Acidosis only decreased the length and area of CA SMC.6. Lowing pHex augmented ASMCs Ba2+current in CA, attenuated in MA, and did not affect in RIA. There was no difference in the current amplitude change induced by pHin variation in CA and MA SMC.7. Acidic pHex diminished SMC Kv current of CA specifically, and did not alter the amplitude of KV current in RIA and MA ASMCs:8. Acidic pHex increased ASMCs [Ca2+]in in CA specifically, and did not alter [Ca2+]in in RIA and MA. The increasing [Ca2+]in of CA inhibited by Lans and DIDS. Function of DIDS is bigger than Lans. Another inhibitor, Amil, did not vary the [Ca2+]in increasing in CA.9. Acidic pHex led to the increasing pHin in CA and the decreasing pHin in MA. The increasing pHin was reversed by DIDS, and became lowing pHin. Acidosis did not affect the physiological pHin owing to pretreatment of Lans. However, Amil did not alter the increasing pHin induce by acidosis in CA ASMCs. Conclusion:Acidosis induced and contributed to RCA constriction, while did not affect significantly the basic force of RIA and MA. Acidic pHex enhanced LTCC current and decreased KV current of RCA ASMCs. Lower pHex and alkalized pHin increased both its LTCC current amplitude. The cytoplasmic alkalization induced by acidic pHex was attenuated by Na+/HCO3-transporter inhibitor (DIDS) and proton pump inhibitor (Lans) in RCA ASMCs. According to the above results, we thought that vasoconstriction, pHin increasing and the changes of electrophysiological characteristics were involved in Na+/HCO3-transporter and proton pump of cell membrane in RCA ASMCs.