Figure 9. Hypothetical distribution of K_Ca channel subunits to account for the tonotopic organization of the turtle cochlea.

The hair cell concentration of each isoform is plotted against distance along the cochlea from the low-frequency end. Only the 31:3 α+β, 4:3 α+β, 4:-26 α+β, 4:61 α, and 0:0 α variants are shown, calculated as overlapping Gaussian distributions in decreasing order of time constant. Experimental values for the relaxation time constant (τ) and half-saturating [Ca²⁺] (Ca_0.5) at -50 mV for the different variants are shown above the plot. The Ca_0.5 values given in parentheses were obtained for the avian β2; all other values are for bovine β. Evidence in support of the scheme is described in the text.