Analysis of ionic channels of medullary respiratory neurons by whole-cell patch-clamp recordings

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The purpose of the present study was to analyze properties of membrane ionic channels of mammalian medullary respiratory neurons by whole-cell patch-clamp recordings. I focused on analysis of mainly Ca channels of pre-inspiratory (Pre-I), inspiratory (Insp) and tonic-expiratory (Exp) neurons in brainstem-spinal cord preparations isolated from newborn rats. These respiratory neurons were recorded in the rostral ventrolateral medulla. After Na-channel blockade by TTX and K-channel blockade by Cs^+ and TEA^+, at least 4types of Ca-dependent membrane potential responses were revealed : 1) High-threshold Ca^<2+> spike (HTS) which has the threshold of -40 to -20mV.The HTS was observed in all types of respiratory neurons analyzed. 2) Rebound responses including low-threshold Ca^<2+> spike (LTS) ; depolarizing responses to termination of hyperpolarizing current pulses. The LTS that was induced at holding potential below -50mV,was observed frequently in Pre-I,Insp or Exp neurons that tended to … More show continuous firings (i.e.tonic pacemaker activity) in the perfusate with or without TTX.3) Low-threshold Ca^<2+> after-depolarization (L-ADP). This was observed at holding potential more negative than -45 to -50 mV and the amplitude increased with progressive membrane hyperpolarization. The L-ADP was observed in some Insp neurons. 4) Intermediate-threshold Ca^<2+> plateau potential (ITP) of which threshold ranged from -50 to -40mV.This response was characterized with slow regenerative depolarization induced by brief depolarization from resting potential level (about -50mV) and with afterdepolarization at termination of depolarizing current pulse injection. The amplitude decreased with membrane hyperpolarization. The ITP was detected in about half of Pre-I neurons and type III (receiving inhibitory synaptic input from Pre-I) Insp neurons. Pharmacological study suggested that P-and also N-type Ca channels are involved in ITP responses. The present study shows that medullary respiratory neurons in newborn rat preparations have a complex set of Ca-dependent membrane conductances, which may be relevant for the respiratory burst generation and maintenance. Less