Concentration-response relationship for protons with or without the pre-application of prokineticin 2. (A) Sequential currents evoked by different pHs in the absence or presence of PK2. (B) The concentration-response curves for protons with or without PK2 (1 nM) pre-application. Each point represents the mean ± SEM of 7 to 11 neurons. All current values were normalized to the current response induced by pH 4.5 applied alone (marked with asterisk). The curves shown are a best fit of the data to the logistic equation I = I
max/[1 + (EC50/C)n], where C is the concentration of protons, I is the normalized current response value, EC50 is the proton concentration that produced half the maximal current response to protons, and n is the Hill coefficient. The curves for protons without and with PK2 pre-application were drawn according to the equation described above (the Hill coefficients are 1.29 with PK2 pre-application and 1.31 without). The pretreatment of PK2 shifts the concentration-response curve for protons upwards. PK2: prokineticin 2; SEM: standard error of the mean.