Significance of extracellular potassium in central respiratory control studied in the isolated brainstem-spinal cord preparation of the neonatal rat.
The significance of extracellular potassium in central respiratory control was investigated using the isolated brainstem-spinal cord preparation of the neonatal rat. Depth profiles of extracellular potassium activity ([K+])ECF in the medulla were measured with ion-sensitive microelectrodes. Although [K+]ECF increased with depth in medullary tissue during control (4 mM) and low (1 mM) potassium concentration ([K+])CSF superfusion, this gradient disappeared with higher [K+]CSF. With low [K+]CSF (1 mM), respiratory CO2 responsiveness was abolished, and increased with high [K+]CSF (8 mM). Respiratory frequency (fR) was diminished at low [K+]CSF (1 mM), and increased with elevated [K+]CSF (8 and 16 mM); with yet higher [K+]CSF (32 mM) apnea occurred after a transient increase in fR. Perforated patch recording revealed that high [K+]ECF decreased membrane resistance, depolarized membrane potential, and increased firing frequency in most of the recorded medullary neurons. High [K+]ECF also increased excitatory and inhibitory post-synaptic potentials of medullary neurons and augmented the functional connectivity among neurons. It is concluded that [K+]ECF is of importance in the maintenance of respiratory rhythm and central chemosensitivity.
Okada
Yasumasa
Y
Department of Medicine, Keio University Tsukigase Rehabilitation Center, Tsukigase 380-2, Izu City, Shizuoka-ken 410-3215, Japan. yasumasaokada@1979.jukuin.keio.ac.jp
Kuwana
Shun-ichi
S
Kawai
Akira
A
Mückenhoff
Klaus
K
Scheid
Peter
P
D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001933:Brain Stem / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D002245:Carbon Dioxide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000187:drug effects*; D066298:In Vitro Techniques; D017736:Ion-Selective Electrodes; D008564:Membrane Potentials / Q000187:drug effects; D009433:Neural Inhibition / Q000187:drug effects; D009474:Neurons / Q000145:classification / Q000187:drug effects*; D018408:Patch-Clamp Techniques / Q000379:methods; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012119:Respiration / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects* / Q000502:physiology
D002245:Carbon Dioxide; D011188:Potassium