Inhibitory Effect Of Acidic PH Activated Chloride Channel In Severe Acidosis Induced Contraction From Aorta Of Spontaneously Hypertensive Rats

BackgroundThe extracellular pH (pHo) is generally maintained within a narrow limits, between7.35and7.45, but some pathological conditions, such as ischemia and hypoxia, metabolic disorders, gastrointestinal disorders and renal dysfunction may cause partical even whole extracellular acidosis. Increasing evidences revealed that extracellular acidosis could modulate the vascular tone, such as vasoconstriction effect of aorta in rest and vasodilation effect of aorta precontracted by phenylephrine, and the different results may be induced by different levels of acidosis. Otherwise, the reaction was changed in hypertension.More recently, a novel type of chloride channel activated by severe acidic solution (Icl,acid) had been found in a variety of mammalian cell types such as HEK.-293cells, cardiac myocytes, monocytes and so on. This channel was activated by very acidic extracellular conditions (pHo below5.5), exhibited outward rectification and inhibited by anion channel inhibitor4,4’-diisothiocyanostilbene-2,2’-disulphonic acid(DIDS). Then we studied the role of Icl,acidin severe acidosis induced aorta contraction and in hypertension.Objective1. To observe the change of angiotasis of thoracic aortic rings from both SHR and Wistar rats in different pHo;2. To discuss the role of Ca2+and Icl,acid in severe acidosis induced contraction of thoracic aorta from SHR and Wistar rats;3. To discuss the change of Icl,acid current of SHR aorta smooth muscle cells(SMCs) in severe acidosis.Method12-13weeks old male SHR and age-matched Wistar rats were used in this investigation (n=6for each group). Isometric tension in rat aortas was measured in various acidic pHo(pHo=7.4,6.4,5.4and4.4), also in the presence of chlorine channel inhibitors DIDS (10-4M) and5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB,10-4M), VDCC inhibitor Nifedipine (10-5M) and in calcium free enviroment. The chlorine current density in rat SMCs was detected by whole-cell patch clamp in severe acidic pHo(pHo=7.4and4.4), also in the presence of chlorine channel inhibitors DIDS (10"4M) and NPPB (10-4M).Results1. Effect of slight and severe acidosis on resting tension of thoracic aorta from SHR and Wistar ratsSlight and severe acidosis increased resting tension of thoracic aorta from both SHR and Wistar rats, but there was no difference among the contractions at pHo6.4, pHo5.4and pHo4.4in Wistar rats (P<0.05), as well as at pHo5.4and pHo4.4in SHR (P<0.05). Compared with Wistar rats, acidosis induced contraction in SHR was greater (P<0.05). There was no difference between endothelium-intact and endothelium-denuded thoracic aorta rings (P>0.05)2. Effect of calcium free solution and nifedipine on acidosis induced contraction of thoracic aorta from SHR and Wistar ratsIn calcium-free extracellular solution, acidosis-induced contraction at each pH0was inhibited. VDCC blocker nifedipine (10-5M) also inhibited acidosis induced contraction of thoracic aorta from both SHR and Wistar rats. With nifedipine, the remnant contraction at pHo5.4was higher than that at pHo6.4and pHo4.4(P<0.05). At every pHo, the remnant contractions of SHR were greater than that of normaltensive Wistar rats(P<0.05).3. Effect of chlorine channel inhibitors DIDS and NPPB on acidosis induced contraction of thoracic aorta from SHR and Wistar ratsChloride channel blockers DIDS (10-4M) and NPPB (10-4M) inhibited acidosis induced contraction of thoracic aorta from both SHR and Wistar rats at different pHo. With DIDS and NPPB, the remnant contraction at pHo4.4was higher than that at pH06.4and pHo5.4(P<0.05). At every pHo, the remnant contractions of SHR were greater than that of normaltensive Wistar rats(P<0.05).4. Effect of severe acidosis on IcI, acid chlorine current of smooth muscle cells from SHR and Wistar rats aortaAn outward current was recorded at pHo4.4and current-voltage relationships showed that the current exhibited a clear outward rectification which could be inhibited by DIDS and NPPB. Compared with Wistar rats, the chlorine current density of SMCs from SHR significantly decreased(P<0.05).Conclusion1. The exposure of SHR and Wistar rats thoracic aortic rings in resting potential to extracellular acidosis caused vasoconstriction effects;2. Both extracellular calcium influx and intracellular calcium mobilization took part it in the vasoconstriction effects caused by acid pHo;3-IcI, activactivation inhibited the vasoconstriction effects caused by severe acid pHo;4. SHR thoracic aortic rings contracted more serious under acid pHo, and the inhibition effect of ICI.cid activation decreased in SHR.