Urotensin II promotes vagal‐mediated bradycardia by activating cardiac‐projecting parasympathetic neurons of nucleus ambiguus

Abstract

Urotensin II (U-II) is a cyclic undecapeptide that regulates cardiovascular function at central and peripheral sites. The functional role of U-II nucleus ambiguus, a key site controlling cardiac tone, has not been established, despite the identification of U-II and its receptor at this level. We report here that U-II produces an increase in cytosolic Ca2+ concentration in retrogradely labeled cardiac vagal neurons of nucleus ambiguus via two pathways: (i) Ca2+ release from the endoplasmic reticulum via inositol 1,4,5-trisphosphate receptor; and (ii) Ca2+ influx through P/Q-type Ca2+ channels. In addition, U-II depolarizes cultured cardiac parasympathetic neurons. Microinjection of increasing concentrations of U-II into nucleus ambiguus elicits dose-dependent bradycardia in conscious rats, indicating the in vivo activation of the cholinergic pathway controlling the heart rate. Both the in vitro and in vivo effects were abolished by the urotensin receptor antagonist, urantide. Our findings suggest that, in addition, to the previously reported increase in sympathetic outflow, U-II activates cardiac vagal neurons of nucleus ambiguus, which may contribute to cardioprotection.

Modulation of cardiac vagal tone by bradykinin acting on nucleus ambiguus

“…Cardiac vagal neurons of nucleus ambiguus were retrogradely labeled by intrapericardial injection of rhodamine [X-rhodamine-5-(and-6)-isothiocyanate; 5(6)-XRITC], 40 µl, 0.01%, (Invitrogen, ThermoFisher Scientific, Grand Island, NY), as previously reported (Brailoiu et al, 2014a, Brailoiu et al, 2014b). 24 h after rhodamine injection, rats were euthanized by decapitation, and the brains quickly removed and immersed in ice-cold Hanks’ balanced salt solution (HBSS; Mediatech, Manassas, VA).…”

“…The intracellular Ca 2+ concentration, [Ca 2+ ] i , was assessed, as previously described, in neurons loaded with Fura-2 AM (Brailoiu et al, 2014a, Brailoiu et al, 2014b). Neurons were incubated with Fura-2 AM (5 µM in HBSS, 45 min, at room temperature).…”

“…The changes of membrane potential were assessed in neurons loaded with bis-(1,3-dibutylbarbituric acid)-trimethine-oxonol, DiBAC 4 (3), a voltage-sensitive dye, as reported (Brailoiu et al, 2014a, Brailoiu et al, 2014b). Neurons were incubated with DiBAC 4 (3) (0.5 mM in HBSS, 30 min) and the fluorescence (excitation/emission 480nm/540nm) was monitored.…”

“…Adult male rats (250–300 g) were anesthetized with ketamine hydrochloride (100–150 mg/kg) and acepromazine maleate (0.2 mg/kg), as previously reported (Brailoiu et al, 2014a, Brailoiu et al, 2014b). Nucleus ambiguus was identified based on stereotaxic coordinates (12.24 mm posterior to bregma, 2.1 mm from midline and 8.2 mm ventral to the dura mater); a guide C315G cannula was bilaterally inserted into the nucleus ambiguus.…”

Identification of snake bradykinin-potentiating peptides (BPPs)-simile sequences in rat brain – Potential BPP-like precursor protein?

“…Considering that the rat SOD enzyme has a key role in regulating the BP, acting as an endogenous antioxidant [67], it would be expected that peptide fragments derived from SOD protein sequence could be biologically effective only in conditions suitable for the antioxidant system's triggering. It is well-known that SOD, as an antioxidant, acts in the CNS by reducing the levels of reactive oxygen species (ROS), which in turn increases the excitability of sympathetic premotor neurons, subsequently reducing the sympathetic tone [68], although vagalmediated increase in parasympathetic tone could not be ruled out [69][70][71][72], as angiotensinconverting enzyme (ACE) inhibitors can significantly increase vagal tone [71,72]. Therefore, it would be conceivable that after this primary action, SOD could also be the source of bioactive peptides that could further decrease the BP by a mechanism of action that still need to be unraveled.…”