Differential responses of porcine anterior spinal and middle cerebral arteries to carbon dioxide and pH

Coronary hypercontractility to acidosis owes to the greater activity of TMEM16A/ANO1 in the arterial smooth muscle cells

BACKGROUND

Severe acidosis deteriorates cardiac injury. Rat coronary arteries (RCAs) are unusually hypercontractive to extracellular (o) acidosis (EA). TMEM16A-encoded anoctamin 1 (ANO1), a Ca²⁺-activated chloride channel (CaCC), plays an important role in regulating coronary arterial tension.

PURPOSE

We tested the possibility that the activation of CaCCs in the arterial smooth muscle cell (ASMC) contributes to EA-induced RCA constriction.

METHODS

ANO1 expression was detected with immunofluorescence staining and Western blot. TMEM16A mRNA was assessed with quantitative Real-Time PCR. Cl^- currents and membrane potentials were quantified with a patch clamp. The vascular tension was recorded with a myograph. Intracellular (i) level of Cl^- and Ca²⁺ was measured with fluorescent molecular probes.

RESULTS

ANO1 was expressed in all tested arterial myocytes, but was much more abundant in RCA ASMCs as compared with ASMCs isolated from rat cerebral basilar, intrarenal and mesenteric arteries. EA reduced [Cl^-]_i levels, augmented CaCC currents exclusively in RCA ASMCs and depolarized RCA ASMCs to a greater extent. Cl^- deprivation, which depleted [Cl^-]_i by incubating the arteries or their ASMCs in Cl^--free bath solution, decreased EA-induced [Cl^-]_i reduction, diminished EA-induced CaCC augmentation and time-dependently depressed EA-induced RCA constriction. Inhibitor studies showed that these EA-induced effects including RCA constriction, CaCC current augmentation, [Cl^-]_i reduction and/or [Ca²⁺]_i elevation were depressed by various Cl^- channel blockers, [Ca²⁺]_i release inhibitors and L-type voltage-gated Ca²⁺ channel inhibitor nifedipine. ANO1 antibody attenuated all observed changes induced by EA in RCA ASMCs.

CONCLUSION

The greater activity of RCA ASMC CaCCs complicated with an enhanced Ca²⁺ mobilization from both [Ca²⁺]_i release and [Ca²⁺]_o influx plays a pivotal role in the distinctive hypercontractility of RCAs to acidosis. Translation of these findings to human beings may lead to a new conception in our understanding and treating cardiac complications in severe acidosis.

Paradoxical effects of acidosis on the noradrenaline-induced and neurogenic constriction of the rat tail artery at low temperatures

Although vasodilatation evoked by acidosis at normal body temperature is well known, the reports regarding effect of acidosis on the reactivity of the isolated arteries at low temperatures are nonexistent. This study tested the hypothesis that the inhibitory effect of acidosis on the neurogenic vasoconstriction may be increased by cooling. Using wire myography, we recorded the neurogenic contraction of the rat tail artery segments to the electrical field stimulation in the absence and in the presence of 0.03-10.0 µmol/L noradrenaline. The experiments were conducted at 37 °C or 25 °C and pH 7.4 or 6.6 which was decreased by means of CO₂. Noradrenaline at concentration of 0.03-0.1 µmol/L significantly potentiated the neurogenic vasoconstriction at 25 °C, and the potentiation was not inhibited by acidosis. Contrary to our hypothesis, acidosis at a low temperature did not affect the noradrenaline-induced tone and significantly increased the neurogenic contraction of the artery segments in the absence and presence of noradrenaline. These effects of acidosis were partly dependent on the endothelium and L-type Ca²⁺ channels activation. The phenomenon described for the first time might be of importance for the reduction in the heat loss by virtue of decrease in the subcutaneous blood flow at low ambient temperatures.

PACAP and VIP differentially preserve neurovascular reactivity after global cerebral ischemia in newborn pigs

Pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are neuroprotective in numerous models. Impairment of cerebrovascular reactivity (CR) contributes to ischemia/reperfusion (I/R)-induced neuronal damage. We tested whether PACAP and/or VIP preserve CR to I/R-sensitive dilator responses dependent on endothelial and/or neuronal function. Accordingly, changes in pial arteriolar diameters in response to hypercapnia (5-10% CO(2) ventilation) or topical N-methyl-d-aspartate (NMDA, 10(-4) M) were determined before and after I/R via intravital microscopy in anesthetized/ventilated piglets. Local pretreatment with non-vasoactive doses of PACAP (10(-8) M) and VIP (10(-9) M) prevented the attenuation of postischemic CR to hypercapnia; to 10% CO(2), the CR values were 27+/-8% vs 92+/-5% vs 88+/-13% (vehicle vs PACAP38 vs VIP, CR expressed as a percentage of the response before I/R, mean+/-SEM, n=8-8, p<0.05). PACAP, but not VIP, preserved CR to NMDA after I/R, with CR values of 31+/-10% vs 87+/-8% vs 35+/-12% (vehicle vs PACAP38 vs VIP, n=6-6). Unlike PACAP, VIP-induced vasodilation has not yet been investigated in the piglet. We tested whether VIP-induced arteriolar dilation was sensitive to inhibitors of cyclooxygenase (COX)-1 (SC-560, 1 mg/kg), COX-2 (NS-398, 1 mg/kg), indomethacin (5 mg/kg), and nitric oxide synthase (L-NAME, 15 mg/kg). VIP (10(-8)-10(-7)-10(-6) M, n=8) induced reproducible, dose-dependent vasodilation of 16+/-3%, 33+/-6%, and 70+/-8%. The response was unaffected by all drugs, except that the vasodilation to 10(-8) M VIP was abolished by SC-560 and indomethacin. In conclusion, PACAP and VIP differentially preserve postischemic CR; independent of their vasodilatory effect.