Dynamic Changes in Extracellular Na⁺, Cl^-, and Ca²⁺ Concentration

Abstract

In addition to [K⁺]_e changes, neuronal activity is accompanied by changes in the concentration of other ions in the microenvironment of the CNS and receptor organs. In the case of Na⁺ and Cl^- it is difficult to measure the changes directly, since the sensitivity of the relevant ISMs is relatively small in the high resting extracellular concentration of these ions. Changes in Na⁺ and Cl^- can therefore only be measured when they exceed several mmol/l; they are thus hard to demonstrate during electrical stimulation and impossible to demonstrate during adequate stimulation. However, the dramatic changes (i.e., the decrease in [Na⁺]_e and in [Cl^-]_e) which occur during anoxia, epilepsy, and spreading depression can be measured dynamically (see Fig. 45; Nicholson 1980; Nicholson et al. 1981).