6‐Nitrodopamine Potentiates Catecholamine‐Induced Ca ²⁺ i Release in Human Aortic Smooth Muscle and Modulates Vascular Smooth Muscle Contractility

Figures

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  FIGURE 1. Effect of 6‐nitrodopamine (6‐ND), noradrenaline (NA), adrenaline (ADR) and dopamine (DA) on intracellular calcium ([Ca2+]i) in human aortic smooth muscle cells. Panels A and B show the concentration‐dependent increases in [Ca2+]i induced by 6‐ND, NA, ADR and DA, as measured by the peak increase and area under the curve, respectively. Panels C to F show accumulated traces of [Ca2+]i increase at 6‐ND 1 nM (C), NA 1 μM (D), ADR 1 μM (E) and DA 10 nM (F). Data are expressed as mean ± SEM.

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  FIGURE 2. Effect of 6‐nitrodopamine (6‐ND), noradrenaline (NA), adrenaline (ADR) and dopamine (DA) on concentration‐dependent increases in intracellular calcium ([Ca2+]i) in human aortic smooth muscle cells in Hanks’ balanced salt solution (HBSS), with Ca2+ and nominally Ca2+‐free. Panels A, B and C show the effect of 6‐ND on [Ca2+]i, measured by the peak increase and area under the curve (AUC), respectively. Panels D, E and F show the effect of NA on [Ca2+]i, measured by the peak increase, AUC and accumulated [Ca2+]i traces, respectively. Panels G, H and I represent the effect of ADR, and Panels J, K and L represent the effect of DA, on [Ca2+]i as measured by these same parameters. *p < 0.05. Data are expressed as mean ± SEM.

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  FIGURE 3. Synergistic effect of 6‐nitrodopamine (6‐ND) on catecholamine‐induced intracellular calcium ([Ca2+]i) increase in human aortic smooth muscle cells. Panels A, B and C show that pre‐incubation with 6‐ND (1 pM) enhanced the effect of noradrenaline (NA) on [Ca2+]i increase, as measured by the peak increase, area under the curve (AUC) and accumulated [Ca2+]i traces, respectively. Panels D, E and F demonstrate that pre‐incubation with 6‐ND (1 pM) enhanced the effect of adrenaline (ADR) on [Ca2+]i increase, as measured by the peak increase, AUC and accumulated [Ca2+]i traces, respectively. Panels G, H and I show that pre‐incubation with 6‐ND (1 pM) similarly enhanced the effect of DA on [Ca2+]i increase, as measured by the peak increase, AUC and accumulated [Ca2+]i traces, respectively. a,b p < 0.05 compared with 6‐ND (1 pM) and NA, ADR or DA (30 pM). Data are expressed as mean ± SEM.

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  FIGURE 4. Effect of 6‐nitrodopamine (6‐ND) on concentration‐dependent contractions of isolated rat thoracic aortic rings without endothelium, induced by noradrenaline, adrenaline and dopamine. Panels A to C show the concentration‐dependent contractions induced by noradrenaline (NA; 100 pM–100 μM), in the absence or presence of 6‐ND 1 pM (A), 10 pM (B) and 100 pM (C). Panels D to F illustrate the effect of adrenaline (ADR; 100 pM–100 μM) on contraction, in the absence or presence of 6‐ND 1 pM (D), 10 pM (E) and 100 pM (F). Panels G to I show the effect of dopamine (DA; 100 pM–100 μM), in the absence or presence of 6‐ND 1 pM (G), 10 pM (H) and 100 pM (I). *p < 0.05. Data are expressed as mean ± SEM.

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  FIGURE 5. Effect of tetrodotoxin (TTX) on 6‐nitrodopamine (6‐ND), noradrenaline (NA), adrenaline (ADR) and dopamine (DA) induced intracellular calcium ([Ca2+]i) increase in human aortic smooth muscle cells. Panels A and B show the effect of TTX (10 and 100 nM) on the 6‐ND–induced [Ca2+]i increase, measured by peak increase (A) and area under the curve (AUC, B). Panels C and D show the effect of TTX (100 nM) on NA‐induced [Ca2+]i increase, measured by peak (C) and AUC (D). Panels E and F present the effect of TTX (100 nM) on ADR‐induced [Ca2+]i increase, measured by peak (E) and AUC (F). Panels G and H show the effect of TTX (100 nM) on DA‐induced [Ca2+]i increase, measured by peak (G) and AUC (H). Values are expressed as mean ± SEM. *p < 0.05 compared with 6‐ND 30 nM or DA 10 nM; # p < 0.05 compared with TTX 10 nM + 6‐ND 30 nM or TTX 10 nM + DA 10 nM. Data are expressed as mean ± SEM.

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  FIGURE 6. Effect of tetrodotoxin (TTX) on 6‐nitrodopamine–induced contractions in isolated rat thoracic aortic rings without endothelium. Concentration–response curves for 6‐ND were obtained under control conditions and after pre‐incubation with TTX (1 μM). Data are expressed as mean ± SEM.

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  FIGURE 7. Effect of nominally Ca2+‐free solution on agonist‐induced contractions in isolated rat thoracic aortic rings without endothelium. Concentration–response curves for contractions induced by 6‐nitrodopamine (6‐ND; A), adrenaline (ADR; B), dopamine (DA; C) and noradrenaline (NA; D) were obtained in Krebs–Henseleit solution (KHS) containing normal Ca2+ or in nominally Ca2+‐free KHS. Data are expressed as mean ± SEM.

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  FIGURE 8. Effect of prazosin on 6‐nitrodopamine (6‐ND) and noradrenaline (NA)–induced contractions in endothelium‐denuded rat thoracic aorta. Concentration–response curves to 6‐ND (A) and NA (B) were obtained in the absence (control) or presence of prazosin (pre‐incubation 30 min, 100 nM), followed by cumulative agonist addition. Data are expressed as mean ± SEM.