Analysis of ionic channels involved in burst generation of respiratory neurons in newborn rat medulla in vitro.

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Respiratory neurons in the ventrolateral medulla have high threshold (N,L types), intermediate threshold (P type) and low threshold (T type) Ca^<2+> channels. Using patch clamp method, we investigated high and intermediate throshold Ca^<2+> channels and Ca^<2+>-dependent K^+ channels which are thought to be important in the burst generation, and persistent Na^<2+> channels which are related to intrinsic oscillation of membrane potentials.[Result] 1) Application of P-type Ca channel blocker, omega-Aga-IVA (0.2muM), reduced the burst amplitude. 2) N-type Ca^<2+> channel blocker, omega-CgTx (2muM) increased the burst amplitude and caused partial inactivation of action potentials. omega-CgTx also reduced spike after-hyperpolarization, probably owing to indirect blockade of Ca^<2+>-dependent K^+ channels. 3) Ca^<2+>-dependent K^+ channel blocker, apamine (0.4-1muM) induced an increase in the burst amplitude and partial inactivation of action potentials. 4) L-type Ca^<2+> channel blocker, ni … More fedipine (20muM) shortened the burst duration. 5) After complete inhibition of the burst activity due to Ca^<2+> channel blockade by 0.1 mM Cb^<2+>, Pre-I neurons showed slow depolarizing responses and depolarization-dependent membrane oscillation. The activation threshold was around-45 mV.Subsequent K^+ channel blockade produced spontaneous bursting activity and depolarizing plateau potentials. These responses were blocked by 0.5muM TTX superfusion. [Discussion] We suggest ionic mechanisms of the burst generation as follows : Intrinsic slow depolarization in Pre-I neurons due to activation of TTX-sensitive persistent Na^<2+> channels and P-type Ca^<2+> channels is important in rising phase of burst activity. Then, N and L-Type Ca^<2+> channels are activated to augment the burst. Ca^<2+>-dependent K^+ channels are thought to participate in maintenance and termination of the burst activity. [Conclusion] We revealed ion channels in respiratory neurons in the ventrolateral medulla and suggested function of these channels for the burst generation. Less