Activation by extracellular chymotrypsin. (A) Example time course of chymotrypsin-evoked current increase in an oocyte expressing MEC-4d/10d + MEC-2 + MEC-6. a and b indicate when the curves shown in B were collected. Current amplitude was measured every 4 s at −85 mV. (B) Whole-cell I-V relationship before (a) and during chymotrypsin application (b). In all cases, chymotypsin-evoked current was blocked by amiloride (300 μM). (C) Chymotrypsin-evoked increase in the amiloride-sensitive current in the presence and absence of MEC-2 and MEC-6.