Multiple Targets of Chemosensitive Signaling in Locus Coeruleus Neurons: Role of K+ and Ca2+ Channels

We studied chemosensitive signaling in locus coeruleus (LC) neurons using both perforated and whole cell patch techniques. Upon inhibition of fast Na ⁺ spikes by tetrodotoxin (TTX), hypercapnic acidosis [HA; 15% CO ₂ , extracellular pH (pH _o ) 6.8] induced small, slow spikes. These spikes were inhibited by Co ²⁺ or nifedipine and were attributed to activation of L-type Ca ²⁺ channels by HA. Upon inhibition of both Na ⁺ and Ca ²⁺ spikes, HA resulted in a membrane depolarization of 3.52 ± 0.61 mV ( n = 17) that was reduced by tetraethylammonium (TEA) (1.49 ± 0.70 mV, n = 7; P < 0.05) and absent (−0.97 ± 0.73 mV, n = 7; P < 0.001) upon exposure to isohydric hypercapnia (IH; 15% CO ₂ , 77 mM HCO , pH _o 7.45). Either HA or IH, but not 50 mM Na-propionate, activated Ca ²⁺ channels. Inhibition of L-type Ca ²⁺ channels by nifedipine reduced HA-induced increased firing rate and eliminated IH-induced increased firing rate. We conclude that chemosensitive signals (e.g., HA or IH) have multiple targets in LC neurons, including TEA-sensitive K ⁺ channels and TWIK-related acid-sensitive K ⁺ (TASK) channels. Furthermore, HA and IH activate L-type Ca ²⁺ channels, and this activation is part of chemosensitive signaling in LC neurons.