Essential role of hemoglobin beta-93-cysteine in posthypoxia facilitation of breathing in conscious mice - PubMed (original) (raw)

Essential role of hemoglobin beta-93-cysteine in posthypoxia facilitation of breathing in conscious mice

Benjamin Gaston et al. J Appl Physiol (1985). 2014.

Abstract

When erythrocyte hemoglobin (Hb) is fully saturated with O2, nitric oxide (NO) covalently binds to the cysteine 93 residue of the Hb β-chain (B93-CYS), forming S-nitrosohemoglobin. Binding of NO is allosterically coupled to the O2 saturation of Hb. As saturation falls, the NO group on B93-CYS is transferred to thiols in the erythrocyte, and in the plasma, forming circulating S-nitrosothiols. Here, we studied whether the changes in ventilation during and following exposure to a hypoxic challenge were dependent on erythrocytic B93-CYS. Studies were performed in conscious mice in which native murine Hb was replaced with human Hb (hB93-CYS mice) and in mice in which murine Hb was replaced with human Hb containing an alanine rather than cysteine at position 93 on the Bchain (hB93-ALA). Both strains expressed human γ-chain Hb, likely allowing a residual element of S-nitrosothiol-dependent signaling. While resting parameters and initial hypoxic (10% O2, 90% N2) ventilatory responses were similar in hB93-CYS mice and hB93-ALA mice, the excitatory ventilatory responses (short-term potentiation) that occurred once the mice were returned to room air were markedly diminished in hB93-ALA mice. Further, short-term potentiation responses were virtually absent in mice with bilateral transection of the carotid sinus nerves. These data demonstrate that hB93-CYS plays an essential role in mediating carotid sinus nerve-dependent short-term potentiation, an important mechanism for recovery from acute hypoxia.

Keywords: S-nitrosothiol; S-nitrosylation; hemoglobin; hypoxia; posthypoxia; ventilation.

Copyright © 2014 the American Physiological Society.

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Figures

Fig. 1.

Fig. 1.

Frequency of breathing (top panel), tidal volume (middle panel), and minute ventilation (bottom panel) in conscious freely moving hB93-CYS mice (n = 15) and hB93-ALA mice (n = 16) before and during a hypoxic challenge (10% O2, 90% N2) and upon subsequent return to room air. The data are presented as means ± SE. Note that the horizontal dashed lines in the panels of Figs. 1–3 and Figs. 5 and 6 denote the average values recorded before hypoxic challenge (data taken from both groups of mice).

Fig. 2.

Fig. 2.

Inspiratory time (top panel), expiratory time (middle panel), and tidal volume/inspiratory time (V

t

/T

i

) (bottom panel) in conscious freely moving hB93-CYS mice (n = 15) and hB93-ALA mice (n = 16) before and during hypoxic challenge (10% O2, 90% N2) and upon return to room air. The data are presented as means ± SE.

Fig. 3.

Fig. 3.

Peak inspiratory (Insp) flow (top panel) and peak expiratory (Exp) flow (bottom panel) in conscious freely moving hB93-CYS mice (n = 15) and hB93-ALA mice (n = 16) before and during hypoxic challenge (10% O2, 90% N2) and upon return to room air. The data are presented as means ± SE.

Fig. 4.

Fig. 4.

Total responses (cumulative %change from pre values) in ventilatory parameters in hB93-CYS mice (n = 15) and hB93-ALA mice (n = 16) during hypoxic challenge (top panel) and upon return to room air (bottom panel). The data are presented as means ± SE. Freq, breathing frequency; V

t

, tidal volume; V

m

, minute ventilation; T

i

, inspiratory time; T

e

, expiratory time; PIF, peak inspiratory flow; PEF, peak expiratory flow; *P < 0.05, significant response. †P < 0.05, hB93-ALA mice vs. hB93-CYS mice.

Fig. 5.

Fig. 5.

Frequency of breathing (top panel), tidal volume (middle panel), and minute ventilation (bottom panel) in conscious freely moving hB93-CYS mice (n = 15) and C57BL6 mice (n = 13) before and during hypoxic challenge (10% O2, 90% N2) and upon subsequent return to room air. The data are presented as means ± SE.

Fig. 6.

Fig. 6.

Frequency of breathing (top panel), tidal volume (middle panel), and minute ventilation (bottom panel) in conscious freely moving sham-operated C57BL6 (SHAM) mice (n = 9) or bilateral carotid sinus nerve-transected C57BL6 (CSNX) mice (n = 9) before and during hypoxic challenge (10% O2, 90% N2) and upon subsequent return to room air. The data are presented as means ± SE.

Fig. 7.

Fig. 7.

Percent fetal hemoglobin in B93-CYS and B93-ALA mice. Each point is from one mouse.

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