Fig. 5. Effect of apical 8-(4-chlorophenylthio)-cyclic AMP (cAMP) on short-circuit current (I_sc) of artificial pondwater (APW)-adapted or high-salinity (HSW)-adapted leech integuments under apical Ca²⁺-free conditions. Ca²⁺ was removed from the apical compartment and, when I_sc had stabilized, transepithelial Na⁺ current (I_Na) and non-Na⁺ currents were determined (Control). cAMP (100 µmol l^-1) and 3-isobutyl-1-methyl-xanthine (1 mmol l^-1) were added. I_Na was determined by apical perfusion with Na⁺-free Ringer (cAMP). Values are means ± S.E.M. (N=6). Hatched columns, I_Na; filled columns, residual non-Na⁺ currents.