SCIENTIFIC THINKING Mercury is known to inhibit the permeability of water channels. To help establish that the protein isolated by Agre's group was a water channel, the researchers incubated groups of RNA-injected oocytes (which thus made aquaporin proteins) in four different solutions: plain buffer, low concentration and high concentration of a mercury chloride (HgCl2) solution, and low concentration of a mercury solution followed by an agent (ME) known to reverse the effects of mercury. The water permeability of the cells was determined by the rate of their osmotic swelling. Interpret the results of this experiment, which are presented in the graph below. Control oocytes not injected with aquaporin RNA were also incubated with buffer and the two concentrations of mercury. Predict what the results of these treatments would be

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1. Observe the graph and note the water permeability (rate of osmotic swelling) for each condition: oocytes in buffer, oocytes in low HgCl2, oocytes in high HgCl2, and oocytes in low HgCl2 followed by ME.
2. Compare the water permeability of oocytes in buffer (control) with those in low and high concentrations of HgCl2. Notice the decrease in water permeability with increasing HgCl2 concentration.
3. Analyze the water permeability of oocytes in low HgCl2 followed by ME. Note that the permeability is restored to a level similar to the control (buffer) condition.
4. Interpret the results: HgCl2 inhibits water permeability in a concentration-dependent manner, indicating that mercury affects the function of aquaporin channels.
5. Predict the results for control oocytes not injected with aquaporin RNA: They should show low water permeability in all conditions (buffer, low HgCl2, high HgCl2) since they lack aquaporin channels.