Fig. 3. Time course of the effects of glutamine on secretion rates of 4th instar Rhodnius Malpighian tubules. The experiment represents a typical rescue protocol. Values are means ± S.E.M. All tubules were started in amino-acid-free control saline and were stimulated with 5-HT at t=0 min. The time of glutamine (20 mmol l^-1) addition is indicated by the arrow. Filled circles indicate tubules exposed to the glutamine (N=8), and open circles indicate control tubules (N=8). Asterisks indicate significant differences from the value for the same group at t=75 min.