Fig. 6. Effects of verapamil on tetraethylammonium (TEA) flux (left ordinate) and differential signal (right ordinate) in the lower, main and distal segments of the Malpighian tubule. Mean values + S.E.M. (N=5) are shown for the same tubules before (filled bars) and 20–30 min after (open bars) the addition of verapamil (5 µmol l^–1) to saline containing 100 µmol l^–1 TEA. The asterisk indicates a significant (P<0.05) reduction in TEA influx after the addition of verapamil.