Fig. 8. Effects of 1 mmoll^-1 NaCN, cAMP and cGMP on voltage differences measured by self-referencing K⁺ microelectrodes. (A) In the lower segment, only NaCN significantly altered K⁺ microelectrode voltage (N=18–24 sites on 5–6 tubules). (B) In the main segment, K⁺ microelectrode voltage was altered significantly (P>0.05) by NaCN, cGMP and cAMP (N=16–27 sites on 4–8 tubules). (C) In the distal segment, none of the stimulants or inhibitors had a significant effect on K⁺ microelectrode voltage (N=10–15 sites on 3–5 tubules). Values are means ± S.E.M. Note that positive voltages denote increases in [K⁺] of the unstirred layer relative to the bath and negative voltages denote decreases in [K⁺] of the unstirred layer relative to the bath.