Effects of carbon dioxide on extracellular potassium accumulation and volume in isolated frog spinal cord

A 6–10-fold increase inpCO₂ in the superfusing Ringer solution increased the volume of the extracellular space (ECS) and changed the spatial distribution and amplitude of the extracellular K⁺ accumulation which resulted from dorsal root stimulation. Using the increase in tetraethylammonium concentration (TEA⁺]) resulting from iontophoretic injection of that ion in the extracellular fluid as an indication of the volume of the ECS, it was found that in highpCO₂ the ECS volume in spinal dorsal horn increased by more than 60%. In addition, in the presence of raisedpCO₂ we also observed the following: (1) The rate of diffusion of TEA⁺ into the dorsal horn increased. (2) The accumulation of K⁺ ovoked by single or tetanic stimulation of the dorsal root was less. (3) The clearance of K⁺ was slowed down. (4) The regions where K⁺ accumulated were more restricted. (5) The K⁺ evoked depolarization of the primary afferent fibres decreased. (6) In contrast to TEA⁺, the rate of diffusion of K⁺ into the dorsal horn decreased. The effects of an increase inpCO₂ on K⁺ accumulation and clearance appear to result from an increase in ECS volume and a possible decrease in glial electrical coupling which interferes with glial spatial buffering of K⁺.