Gene Transfer of Neuronal Nitric Oxide Synthase to Carotid Body Reverses Enhanced Chemoreceptor Function in Heart Failure Rabbits

Abstract

Abstract-Our previous studies showed that decreased nitric oxide (NO) production enhanced carotid body (CB) chemoreceptor activity in chronic heart failure (CHF) rabbits. In the present study, we investigated the effects of neuronal NO synthase (nNOS) gene transfer on CB chemoreceptor activity in CHF rabbits. The nNOS protein expression and NO production were suppressed in CBs (PϽ0.05) of CHF rabbits, but were increased 3 days after application of an adenovirus expressing nNOS (Ad.nNOS) to the CB. As a control, nNOS and NO levels in CHF CBs were not affected by Ad.EGFP. Baseline single-fiber discharge during normoxia and the response to hypoxia were enhanced (PϽ0.05) from CB chemoreceptors in CHF versus sham rabbits. Ad.nNOS decreased the baseline discharge (4.5Ϯ0.3 versus 7.3Ϯ0.4 imp/s at 105Ϯ1.9 mm Hg) and the response to hypoxia (18.3Ϯ1.2 imp/s versus 35.6Ϯ1.1 at 40Ϯ2.1 mm Hg) from CB chemoreceptors in CHF rabbits (Ad.nNOS CB versus contralateral noninfected CB respectively, PϽ0.05). A specific nNOS inhibitor, S-Methyl-L-thiocitrulline (SMTC), fully inhibited the effect of Ad.nNOS on the enhanced CB activity in CHF rabbits. In addition, nNOS gene transfer to the CBs also significantly blunted the baseline renal sympathetic nerve activity (RSNA) and the response of RSNA to hypoxia in CHF rabbits (PϽ0.05). These results indicate that decreased endogenous nNOS activity in the CB plays an important role in the enhanced activity of the CB chemoreceptors and peripheral chemoreflex function in CHF rabbits. (Circ Res. 2005;97:260-267.)Key Words: nitric oxide Ⅲ gene transfer Ⅲ chemoreceptor Ⅲ hypoxia Ⅲ heart failure T he endogenous production of nitric oxide (NO) plays an important role in cardiovascular homeostasis through its action on the central and peripheral autonomic nervous systems. 1 Although NO plays a significant excitatory role in the nucleus tractus solitarii (NTS), 2-4 many studies have shown that NO produced within the carotid body (CB) is an inhibitory modulator of CB chemoreceptor activity. [5][6][7][8][9][10][11] For example, the administration of the precursor L-arginine, NO donor molecules, 5,6,9 or NO gas 8 to the cat CB perfused in vitro reduces the chemoreceptor response to hypoxia. Conversely, inhibition of nitric oxide synthase (NOS) increases the frequency of CB chemoreceptor discharge in situ and in vitro. 5,12,13 Profound activation of the sympathetic nervous system is characteristic of chronic heart failure (CHF). 14 -16 Peripheral chemoreceptor activation is an excitatory input that increases sympathetic outflow. 17 Peripheral chemoreceptor sensitivity is enhanced in both clinical and experimental CHF 18 -20 and contributes to the tonic elevation in sympathetic function. Our recent studies have shown that a decreased NO production is involved in the enhanced CB chemoreceptor activity in CHF. 13 We found that NOS inhibition enhanced the sensitivity of the CB chemoreceptors 13 and decreased the CB glomus cell outward potassium currents (I K ) 21 in sham rabbits but was without effect in ...

Expression of Neuronal Nitric Oxide Synthase in Rabbit Carotid Body Glomus Cells Regulates Large-Conductance Ca2+-Activated Potassium Currents

“…A specific nNOS inhibitor (SMTC) totally abolished the effect of Ad.nNOS on the K ϩ current in the CB glomus cells from CHF rabbits and also reduced the K ϩ currents in the CB glomus cells from sham rabbits, regardless of gene transfer of Ad.nNOS. Our previous study has demonstrated that Ad.nNOS gene transfer to the CB reverses the enhanced CB chemoreceptor activity and peripheral chemoreflex sensitivity in CHF rabbits (Li et al 2005). These data suggest that the nNOS down-regulation in CB glomus cells reduces the outward K ϩ currents and contributes to the enhanced chemoreceptor activity in CHF rabbits.…”

“…Although our studies have found that NO plays an important role in regulating K ϩ channels of glomus cells, chemoreceptor discharge, and chemoreflex sensitivity in sham and CHF rabbits (Ding et al 2008;Li et al 2004Li et al , 2005Sun et al 1999b), it is unclear whether NOS is present in the rabbit CB glomus cell. In rats and cats, NOS was found to exist in the extensive plexus of nerve fibers and vessels surrounding glomus cells, but not within glomus cells (Dvorakova and Kummer 2005;Wang et al 1993Wang et al , 1994.…”

“…Our previous study documented that a decreased availability of NO reduced K ϩ currents in CB glomus cells from CHF rabbits. Further, we ascertained that down-regulation of NO synthesis in the CB from CHF rabbits contributed to the CB chemoreceptor hypersensitivity (Sun et al 1999b) and transgene overexpression of nNOS (adenoviral nNOS [Ad.nNOS]) significantly reversed enhanced chemoreceptor function in CHF rabbits (Li et al 2005). Therefore our first purpose in the present study was to test the effect of Ad.nNOS on the K ϩ currents in sham and CHF CB glomus cells.…”

Arterial Chemoreceptors and Sympathetic Nerve Activity

“…During this interval, unpaced left ventricular contractility and ejection fraction decline to levels equivalent to moderate compensated CHF in patients. 24,26,27 Single-unit discharge activity of CB chemoreceptors, both at rest and in response to hypoxia, is similarly enhanced over the same time course (Figure 2A). 25 This increased central input from the CB provides a tonic excitatory influence on sympathetic outflow, because hyperoxia reduces resting RSNA in CHF but not control animals ( Figure 2B).…”

“…10 However, basal NO production and nNOS expression within the CB are depressed in CHF. 25,26 Thus, the tonic inhibitory effect of NO on the activity of CB chemoreceptors, demonstrated in the CB of normal rabbits, is virtually absent in CHF rabbits. 25 The marked down regulation of endogenous nNOS in the CB plays a major role in the enhanced CB chemoreceptor activity in CHF rabbits.…”