Fig. 2. Effect of basolateral ATP on short-circuit current (I_sc) of artificial pondwater (APW)- and high-salinity (HSW)-adapted integuments. Transepithelial Na⁺ current was determined after I_sc had reached steady state (control). Subsequently 1 mmol l^-1 ATP was added to the basolateral compartment and transepithelial Na⁺ current (I_Na) was determined again (ATP) when I_sc had stabilized. Values are means ± S.E.M. (N=5). ATP significantly increased I_Na in HSW-adapted preparations, ^**P<0.005. Hatched columns, transepithelial Na⁺ current; filled columns, residual non-Na⁺ currents.