An analysis of potassium distribution in the central nervous system of Bombyx mori

An analysis of potassium distribution in cellular and extracellular compartments of Bombix mori larvae nerve cord was done on the basis of electrophysiological measurements, cation determinations and morphological observations. 2. Sodium and potassium concentrations in the cord were: 43.3 ± 5.5 and 227.2 ± 10.8 mmol/l tissue water, respectively. 3. The measured cellular electrical potentials were correlated with the external potassium concentration [Ko]: V(mV) = 57.8 log ([Ko]/298.1) at [Ko] >= 45.6 mM. 4. The nerve cord, on the basis of electron microscopic observations, was considered a three compartment system: the neuron cell, the extracellular space and the hemolymph. 5. Assuming that the electrical potential difference of the inner barrier is not affected by the ionic composition in the hemolymph, the potassium concentrations in the neuron and in the extracellular space were calculated, and the values are: 298.1 and 14.7 mM, respectively. 6. These results are consistent with the assumption that a well-developed blood-brain barrier plays a role in the regulation of the extraneuronal environment.