Effect of Ciguatoxin on sodium transport across the frog skin

Abstract

The effect of Ciguatoxin (CT) on Na transport across isolated frog skin ( Rana pipiens ) was studied by measuring the electrical potential difference (PD) and the short-circuit current (SCC). When NaCl-Ringer was used, CT (0.25–0.5 mg/100 ml) added to the outside bathing medium induced a substantial reduction in PD and a slight reduction in SCC, indicating a reduction in the skin resistance. The recovery was extremely slow and incomplete. The above reduction in SCC was associated with a significant increase in 22 Na outflux in the face of constant 22 Na influx. The CT effect was much less pronounced and more variable when it was added to the inside bathing medium. When Na 2 SO 4 -Ringer was used, the reduction in PD was smaller than that of SCC. The presence of antidiuretic hormone (ADH) in the inside bathing medium did not alter the response of the skin to CT. Similarly, the presence of CT in the outside bathing medium did not affect the response of the skin to ADH. However, the action of CT was not evident in the presence of 10 m m calcium in the outside bathing medium. CT had no effect on the water permeability of the toad urinary bladder preparation. These results suggest that CT primarily increases the passive permeability of the skin to Na, although an effect on the Na pump cannot be ruled out completely.