Effects of extracellular calcium and magnesium on central respiratory control in the brainstem-spinal cord of neonatal rat.
The influence of extracellular Ca2+ and Mg2+ concentrations ([Ca2+]ECF and [Mg2+]ECF, respectively) on central respiratory control was analyzed using the isolated brainstem-spinal cord of the neonatal rat. Central respiratory activity was recorded from the C4 ventral roots. The depth profile of [Ca2+]ECF below the ventral medullary surface was measured with ion-sensitive electrodes. The gradient in [Ca2+]ECF disappeared about 1 h after changing superfusate Ca2+ ([Ca2+]CSF) from 2 to 0.5 mM, but not even in 2 h after switching to Ca2+-free superfusate. High [Ca2+]CSF (4 mM) or high [Mg2+]CSF (4, 8 mM) decreased respiratory frequency (fR), whereas low [Ca2+]CSF (0.5 mM) increased fR and augmented the respiratory CO2 responsiveness. High [Ca2+]CSF as well as low [Mg2+]CSF (0.5 mM) disturbed respiratory rhythm and pattern, which were markedly restored by high CO2. The depressing effect of high [Ca2+]ECF and the stimulating effect of low [Ca2+]ECF on the medullary neuronal activity were confirmed by perforated patch recordings. These results suggest that [Ca2+]ECF and [Mg2+]ECF determine the excitability of the respiratory neuron network by modulating the neuronal surface potential, transmembrane Ca2+ influx, Ca2+-sensitive cation channel gating, and synaptic transmission. Furthermore, some of these actions appear to be antagonized by CO2/H+.
Kuwana
S
S
Department of Physiology, Teikyo University School of Medicine, Tokyo 173-0003, Japan. kuwanas@med.teikyo-u.ac.jp
Okada
Y
Y
Natsui
T
T
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D001933:Brain Stem / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002628:Chemoreceptor Cells / Q000502:physiology; D003714:Denervation; D005110:Extracellular Space / Q000378:metabolism*; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism*; D008526:Medulla Oblongata / Q000166:cytology / Q000502:physiology; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D012143:Respiratory Physiological Phenomena; D013116:Spinal Cord / Q000502:physiology*
D008274:Magnesium; D002118:Calcium