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Investigation on the positive chronotropic action of 6-nitrodopamine in the rat isolated atria

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Abstract

6-Nitrodopamine (6-ND) is released from rat isolated atria being 100 times more potent than noradrenaline and adrenaline, and 10,000 times more potent than dopamine as a positive chronotropic agent. The present study aimed to investigate the interactions of 6-ND with the classical catecholamines, phosphodiesterase (PDE)-3 and PDE4, and the protein kinase A in rat isolated atria. Atrial incubation with 1 pM of dopamine, noradrenaline, or adrenaline had no effect on atrial frequency. Similar results were observed when the atria were incubated with 0.01 pM of 6-ND. However, co-incubation of 6-ND (0.01 pM) with dopamine, noradrenaline, or adrenaline (1 pM each) resulted in significant increases in atrial rate, which persisted over 30 min after washout of the agonists. The increased atrial frequency induced by co-incubation of 6-ND with the catecholamines was significantly reduced by the voltage-gated sodium channel blocker tetrodotoxin (1 µM, 30 min), indicating that the positive chronotropic effect of 6-ND is due in part to activation of nerve terminals. Pre-treatment of the animals with reserpine had no effect on the positive chronotropic effect induced by dopamine, noradrenaline, or adrenaline; however, reserpine markedly reduced the 6-ND (1 pM)-induced positive chronotropic effect. Incubation of the rat isolated atria with the protein kinase A inhibitor H-89 (1 µM, 30 min) abolished the increased atrial frequency induced by dopamine, noradrenaline, and adrenaline, but only attenuated the increases induced by 6-ND. 6-ND induces catecholamine release from adrenergic terminals and increases atrial frequency independently of PKA activation.

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Acknowledgements

JBJ thanks FAPESP for the post-doctoral fellowship (2021/14414-8). ATL and VF thank FAPESP for PhD fellowship (2021/13593-6, 2022/07737-8). EA and FM thank FAPESP (2017/15175-1). GDN thanks FAPESP (2019/16805-4) and CNPq (303839/2019-8).

Funding

JBJ thanks FAPESP for the post-doctoral fellowship (2021/14414-8). ATL thanks FAPESP for PhD fellowship (2021/13593-6). VF thanks FAPESP for PhD fellowship (2022/07737-8). EA and FM thank FAPESP (2017/15175-1). GDN thanks FAPESP (2019/16805-4) and CNPq (303839/2019-8).

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Contributions

Conceptualization: JBJ, GDN. Data curation: JBJ, GDN. Formal analysis: GDN Funding acquisition: EA, GDN. Investigation: JBJ, ATL, VF, GDN. Methodology: JBJ, ATL, VF, EA, FZM, GDN. Project administration: GDN. Supervision: FZM, EA. Visualization: EA, GDN. Writing—original draft: JBJ, FZM, EA, GDN. The authors declare that all data were generated in-house and that no paper mill was used.

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Correspondence to José Britto-Júnior.

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All experimental protocols were authorized by the Ethics Committee in Animal Use of UNICAMP (CEUA/UNICAMP, protocol numbers 5746-1/2021; 5831-1/2021).

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Fig S01.

Co-incubation of dopamine (DA) with noradrenaline (NA, A) or adrenaline (ADR, B) or co-incubation of noradrenaline with adrenaline (C) on the rat isolated atrium. Data represent the mean ± standard error of the mean (SEM). (PNG 316 kb)

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Britto-Júnior, J., Lima, A.T., Fuguhara, V. et al. Investigation on the positive chronotropic action of 6-nitrodopamine in the rat isolated atria. Naunyn-Schmiedeberg's Arch Pharmacol 396, 1279–1290 (2023). https://doi.org/10.1007/s00210-023-02394-9

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