Fig. 4. Exposure to 30%SW significantly changes the Michealis–Menten kinetics of Na⁺ and Cl^– influx at the papillae. Na⁺ or Cl^– influx was calculated using the measurements obtained from the SIET system from a single point on the surface of the anal papillae while changing the bath NaCl concentration. The results obtained from each individual papilla were fitted to the Michaelis–Menten equation using non-linear regression analysis. J_max, maximum rate of transport; K_t, Na⁺ or Cl^– concentration that yields a flux of 50% J_max. (A) Na⁺ and (B) Cl^– influx from single papillae obtained from larvae maintained in FW (freshwater; squares) or in 30%SW (seawater) for 5 h (triangles). (C) K_t and (D) J_max (means ± s.e.m.) for groups of papillae obtained from larvae that were either held in freshwater (FW), had been transferred from FW to 30%SW for 5 h (30%SW), or were held in 30%SW for 5 h and subsequently transferred to FW (30%SW/FW) for 20 h (Na⁺, white bars, N=6–13) or 5 h (Cl^–, black bars, N=8–13). An asterisk denotes a statistically significant difference from the FW group. Kinetic parameters for Na⁺ (N=6) and Cl^– (N=5) uptake by the papillae of intact larvae (in vivo) held in FW are also shown (no difference from FW, t-test, P<0.05).