FIGURE 4.

Effect of cytosolic and vacuolar K⁺ on single-channel current-voltage relations. (a) Example of single-channel recording on a tiny cytosolic side-out patch bathed in 10-mM K⁺ solution; patch pipette was filled with 100-mM K⁺ solution. Traces were filtered at 1 kHz. Open channel level is indicated by o, dashed line is the baseline corresponding to the closed channel level. (b) Single-channel current amplitudes as a function of membrane voltage were measured in experiments as one presented (a). Pipette (vacuolar side) was filled with 100-mM K⁺ solution; cytosolic side was bathed in solutions with variable K⁺ as indicated (in mM); asterisks are data obtained in 10-mM K⁺ plus 90-mM NMDG⁺ solution. (c) Single-channel current-voltage relationships for vacuolar side-out patches. Pipette (cytosolic side) was filled with 100-mM K⁺ solution, vacuolar K⁺ concentrations (in mM) are indicated. For symmetric 100 mM K⁺, n = 5 patches were analyzed and data are presented as mean ± SD. Those include also controls for two separate experiments where 10 mM K⁺ supplemented by 90-NMDG⁺ solution was tested (asterisks). (d) Single-channel current at potential 100 mV above (cytosolic side-out patch, hollow symbols) or below (vacuolar side-out patches, filled symbols) the reversal potential for single FV channel current as a function of cytosolic or vacuolar K⁺. Data were fitted to Michaelis-Menten equation with dissociation constant values given in the text. Points for 10 mM K⁺ supplemented by 90-mM NMDG⁺ solution (asterisks) are given for the comparison.