The effect of divalent and trivalent cations on the sodium permeability of myelinated nerve fibres of Xenopus laevis.

The effect of external Ca, Mg, Sr, Ba and La concentration was studied in potential clamp experiments on single myelinated nerve fibres of the frog (Xenopus laevis). An increase in cationic concentration caused a positive shift of the Na permeability (PNa) curve along the potential axis, a decrease in max. PNa and a decrease in the slope of the PNa curve. The effectiveness of Mg, Sr and Ba was similar and about 0.6 compared to that of Ca, whereas La was about 80 times more effective than Ca.