Figure 4.

Individual AFM tracings obtained with a ROMK1-coated AFM tip at different pH values (panels 1–6; paired study; i.e., an individual ROMK1-coated AFM tip was subsequently exposed to bath solutions with increasing pH; each experiment was repeated several times to test for the reversibility of the pH response). The catalytic subunit of PKA at 20 milliunits/ml and 0.1 mM ATP were present in the intracellular electrolyte solution to maintain the ROMK1 channel protein in an activatable condition. The tracings in panel 7 were obtained with a noncoated AFM tip. They represent the background noise.