Fluorocitrate-mediated depolarization of astrocytes in the retrotrapezoid nucleus stimulates breathing

Author(s)

Sobrinho, Cleyton R. ; Goncalves, Christopher M. ; Takakura, Ana C. ; Mulkey, Daniel K. ; Moreira, Thiago S.

• Document type: Journal article
• Source: Journal of Neurophysiology; v. 118, n. 3, p. 1690-1697, SEP 2017.
• Web of Science Citations: 6

Abstract

Evidence indicates that CO2 /H+-evoked ATP released from retrotrapezoid nucleus (RTN) astrocytes modulates the activity of CO2-sensitive neurons. RTN astrocytes also sense H+ by inhibition of Kir4.1 channels; however, the relevance of this pH-sensitive current remains unclear since ATP release appears to involve CO2-dependent gating of connexin 26 hemichannels. Considering that depolarization mediated by H+ inhibition of Kir4.1 channels is expected to increase sodium bicarbonate cotransporter (NBC) conductance and favor Ca2+ influx via the sodium calcium exchanger (NCX), we hypothesize that depolarization in the presence of CO2 is sufficient to facilitate ATP release and enhance respiratory output. Here, we confirmed that acute exposure to fluorocitrate (FCt) reversibly depolarizes RTN astrocytes and increased activity of RTN neurons by a purinergic-dependent mechanism. We then made unilateral injections of FCt into the RTN or two other putative chemoreceptor regions (NTS and medullary raphe) to depolarize astrocytes under control conditions and during P2-recepetor blockade while measuring cardiorespiratory activities in urethane-anesthetized, vagotomized, artificially ventilated male Wistar rats. Unilateral injection of FCt into the RTN increased phrenic (PNA) amplitude and frequency without changes in arterial pressure. Unilateral injection of pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS, a P2-receptor antagonist) into the RTN dampened both PNA amplitude and frequency responses to FCt. Injection of MRS2179 (P2Y1-receptor antagonist) into the RTN did not affect the FCt-induced respiratory responses. Fluorocitrate had no effect on breathing when injected into the NTS or raphe. These results suggest that depolarization can facilitate purinergic enhancement of respiratory drive from the RTN. NEW \& NOTEWORTHY Astrocytes in the retrotrapezoid nucleus (RTN) are known to function as respiratory chemoreceptors; however, it is not clear whether changes in voltage contribute to astrocyte chemoreception. We showed that depolarization of RTN astrocytes at constant CO2 levels is sufficient to modulate RTN chemoreception by a purinergic-dependent mechanism. These results support the possibility that astrocyte depolarization can facilitate purinergic enhancement of respiratory drive from the RTN. (AU)

• FAPESP's process: 14/22406-1 - Respiratory anatomofunctional changes observed in an experimental model of Parkinson Disease
• Grantee: Ana Carolina Takakura Moreira
• Support Opportunities: Regular Research Grants
• FAPESP's process: 11/13462-7 - The interaction between retrotrapezoid nucleus astrocytes and neurons on respiratory responses promoted by central chemoreflex activation
• Grantee: Cleyton Roberto Sobrinho
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 15/23376-1 - Retrotrapezoid nucleus, respiratory chemosensitivity and breathing automaticity
• Grantee: Thiago dos Santos Moreira
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 15/12827-2 - Acetylcholine and ventilation: Modulation by cholinergic inputs from pedunculopontine tegmental nucleus to the retrotrapezoid nucleus
• Grantee: Cleyton Roberto Sobrinho
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 16/22069-0 - Amelioration of the brainstem vascular imbalances in an spontaneously hypertensive rats with exercise
• Grantee: Thiago dos Santos Moreira
• Support Opportunities: Regular Research Grants