Intracellular pH Regulation in Neurons from Chemosensitive and Nonchemosensitive Areas of the Medulla

Intracellular pH (pH _i ) regulation was studied in neurons from two chemosensitive [nucleus of the solitary tract (NTS) and ventrolateral medulla (VLM)] and two nonchemosensitive [hypoglossal (Hyp) and inferior olive (IO)] areas of the medulla oblongata. Intrinsic buffering power (β _int ) was the same in neurons from all regions (46 mM/pH U). Na ⁺ /H ⁺ exchange mediated recovery from acidification in all neurons [Ritucci, N. A., J. B. Dean, and R. W. Putnam. Am. J. Physiol. 273 ( Regulatory Integrative Comp. Physiol. 42): R433–R441, 1997]. Cl ⁻ / exchange mediated recovery from alkalinization in VLM, Hyp, and IO neurons but was absent from most NTS neurons. The Na ⁺ /H ⁺ exchanger from NTS and VLM neurons was fully inhibited when extracellular pH (pH _o ) <7.0, whereas the exchanger from Hyp and IO neurons was fully inhibited only when pH _o <6.7. The Cl ⁻ / exchanger from VLM, but not Hyp and IO neurons, was inhibited by pH _o of 7.9. These pH regulatory properties resulted in steeper pH _i -pH _o relationships in neurons from chemosensitive regions compared with those from nonchemosensitive regions. These differences are consistent with a role for changes of pH _i as the proximate signal in central chemoreception and changes of pH _o in modulating pH _i changes.