Figure 3.

Inhibitory activity of PsTx is sensitive to trypsin proteolysis. Shown are currents recorded from outside-out patches containing the α-subunit of the rat olfactory CNG channel. Pipette contains 2 mM cGMP; the extracellular face of the patch was exposed to control solution containing the substances indicated. Voltage pulses were given as described in Fig. 1B. For the panel labeled “Trypsin,” 20 nM PsTx was incubated in control solution containing 100 μg/ml of trypsin for 36 hr. at 37°C. At that time, a 2-fold molar excess of soybean trypsin inhibitor (STI) was added to halt digestion. In the panel labeled “Trypsin + STI,” trypsin and STI were premixed before incubation.