Fig. 4.

Cells of the nhe1⁻ mutant have lost the capacity to undergo K⁺ facilitation and K⁺-dependent chemotactic orientation in a spatial gradient of cAMP but have retained Ca²⁺ facilitation and Ca²⁺-dependent chemotactic orientation. (A) Motility parameters for parental control strain Ax2 and the nhe1⁻ and nhe1⁻/nhe1⁺ strains in 40 mM K⁺ solution and 20 mM Ca²⁺ solution. Chemo. index, chemotactic index; % posit. chemo. proportion of cells with positive chemotactic index. See the legend to Fig. 3 for remaining definitions of abbreviations. Parameters are defined in Materials and Methods. (B) 2-D DIAS-generated stacked perimeter tracks of three representative Ax2, nhe1⁻, and nhe1⁻/nhe1⁺ cells in a spatial gradient of cAMP generated in 40 mM K⁺ solution. (C) 2D-DIAS-generated stacked perimeter tracks of three representative Ax2, nhe1⁻, and nhe1⁻/nhe1⁺ cells in a spatial gradient of cAMP generated in 20 mM Ca²⁺ solution. See the Fig. 3 legend for additional explanations.