Role of glia in K+ and pH homeostasis in the neonatal rat spinal cord

Stimulation‐evoked transient changes in extracellular potassium ([K+]e) and pH (pHe) were studied in the neonatal rat spinal cords isolated from 3–13‐day‐old pups. In unstimulated pups the [K+]e baseline was elevated and pHe was more acid than that in Ringer's solution (3.5 mM K+, pH 7.3–7.35). The [K+]e and pHe in 3–6‐day‐old pups was 3.91 ± 0.12 mM and pHe 7.19 ± 0.01, respectively, while in 10–13‐day‐old pups it was 4.35 ± 0.15 mM and 7.11 ± 0.01, respectively. The [K+]e changes evoked in the dorsal horn by a single electrical stimulus were as large as 1.5–2.5 mM. Such changes in [K+]e are evoked in the adult rat spinal cord with stimulation at a frequency of 10–30 Hz. The maximal changes of 2.1–6.5 mM were found at a stimulation frequency of 10 Hz in 3–6‐day‐old animals. In older animals the [K+]e changes progressively decreased. The poststimulation K+‐undershoot was found after a single stimulus as well as after repetitive stimulation.