Measurement of potassium and chloride ion concentrations in the cupulae of the lateral lines of Xenopus laevis.

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Abstract
Potential measurements were made with double barrel ion selective electrodes from the cupulae of lateral line organs in the aquatic toad X. laevis. A positive endocupular potential (ECP) of 15-50 mV was recorded within the cupula, immediately above the hair cells. Increases in the Cl- and K+ potentials were recorded when the ion selective electrodes touched the cupula. Cupular Cl- and K+ varied between 35-70 mM and 24-100 mM, respectively. This variation existed between, rather than within, different animals. S.c. injections of 0.4 ml 2 mM ouabain greatly reduced the ECP and cupular K+, whereas 0.4 ml of Xenopus Ringer had no effect. Changing the bath Cl- a hundredfold had no effect on the ECP. The ECP was apparently produced by an electrogenic K+ pump which maintained high K+ levels within the cupula.