In vitro effects of extracellular hypercapnic acidification on the reactivity of rat aorta: Rat aorta vasodilation during hypercapnic acidification

• A mixture of CO2 (40%)/O2 (60%) bubbled in organ baths was adequate for producing extracellular acidification.
• Extracellular acidification in arteries pre-contracted with Phe (10−6 M) caused endothelium-dependent relaxation in the pH range from 7.5 to 6.8.
• The relaxation induced by acidification involved the three pathways of signal transduction for endothelium-dependent vasodilation: cGMP/NO, cAMP/PGI2, and hyperpolarization at potassium channels.

The mechanisms by which pH influences vascular tone are not entirely understood, but evidence suggests that the endothelium is involved. Here, we aimed to study the in vitro vascular responses induced by extracellular hypercapnic acidification (HA), as well as the endothelium-dependent mechanisms that are involved in the responses. We bubbled a mixture of CO2 (40%)/O2 (60%) in an organ bath; we constructed a pH-response curve (pH range 7.4–6.6) and registered isometric force simultaneously. Aortic rings from rats were pre-contracted with phenylephrine (10−6 M) and incubated for 30 min in the presence of different chemicals. The relaxations induced by HA occurred in rings with endothelium were: 1) Partially inhibited by indomethacin (10−5 M) (PGI2 pathway inhibitor); 2) Strongly inhibited by NO pathways: L-NAME (10−4 M) and L-NMMA (10−4 M) (no specific NO synthase inhibitors); L-Nil (10−3 M) (specific iNOS inhibitor); ODQ (10−4 M) (specific guanylate cyclase inhibitor), and; 4) Inhibit by tetraethylammonium (10−3 M) (non-specific potassium channel inhibitor), glibenclamide (10−5 M) (specific KATP inhibitor), aminopyridine (10−3 M) (specific Kv inhibitor) and apamin (10−6 M) (specific SKCa inhibitor). In conclusion: 1) HA causes endothelium-dependent relaxation; 2) Indomethacin failed in blocking this relaxation, but the method limitation does not allow ruling out some prostanoid role; 3) The HA vessel relaxation is mediated via cGMP/NO, and; 4) The hyperpolarization occurs by the action of potassium SKCa, KATP and Kv channels without relying on BKCa channels.

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