Intralaryngeal application of ATP evokes apneic response mainly via acting on P2X3/P2X2/3 receptors of the superior laryngeal nerve (SLN) in postnatal rats

Abstract

ATP is reportedly capable of stimulating bronchopulmonary C‐ and/or Aδ‐fibers to evoke apnea, bronchoconstriction, and bradycardia via acting on P2X (P2X2/3) receptors. Stimulation of the SLN evokes apnea, bradycardia, and hypertension, especially in early life. Although P2X3/P2X2/3 receptors are present in the nodose and jugular (N/J) ganglion neurons, it is undetermined whether ATP applied onto the larynx mucosa can elicit the cardiorespiratory responses via activation of P2X3/P2X2/3 receptors of the SLN. To address this issue, the cardiorespiratory responses to intralaryngeal perfusion of ATP (a non‐selective P2‐receptor agonist, 5–10 mg/ml) or α,β‐methylene ATP (a selective P2X‐receptor agonist, 2.5–5 mg/ml) were recorded in anesthetized rat pups (P14‐P18) under the following conditions: 1) before and after bilateral SLN section and 2) immediately after 5 min intralaryngeal pretreatment with saline (Ctrl) or saline containing A‐317491 (a P2X3/P2X2/3 receptor antagonist, 2.5–5 mg/ml). The immunoreactivity (IR) of P2X3 receptor was then identified in N/J ganglion neurons retrogradely traced by DiI that was previously injected into the SLN 10 days ago. Whole‐cell patch clamp recording was used to determine the ATP‐ or α,β‐methylene ATP‐induced currents of N/J neurons in primary culture, particularly those labeled by DiI. We found that intralaryngeal perfusion of ATP and α,β‐methylene ATP induced similar apnea (latency < 1.0 s), hypertension, and bradycardia, which were eliminated after bilateral section of the SLN. A‐317491 but not saline pretreatment attenuated the apneic response to ATP and α,β‐methylene ATP by 63% and 76% respectively and failed to affect the evoked hypertension and bradycardia. P2X3 receptor‐IR was identified in ~35% of both N/J ganglion neurons. 12% of these neurons were labeled by DiI, ~60% of which expressed P2X3 receptor‐IR. Both ATP‐ and α,β‐methylene ATP‐induced currents were recorded in DiI‐labeled neurons. The former was reduced by 75% and the latter abolished by A‐317491. We conclude that ATP and α,β‐methylene ATP applied onto the laryngeal mucosa elicit an apnea predominately through activation of P2X3/P2X2/3 receptors of the SLN.