Fig. 1

Intracellular pH (pH_i) changes induced by ionomycin (IM) in the presence of HCO₃ ⁻. a 5 μM IM in HCO₃ ⁻-containing solution. IM (5 μM) induced no pH_i decrease in Ca²⁺-free solution. The re-introduction of Ca²⁺ induced a large transient pH_i decrease followed by a rapid pH_i increase. The plateau pH_i was slightly higher than that before re-introduction of Ca²⁺. b τ Plot of a. The pH_is for 4 min after re-introduction of Ca²⁺ were used for the τ plot. The τ plot clearly shows that the pH_i increase following the rapid pH_i decrease consisted of two phases: the first phase followed by the second phase. c 1 μM IM in HCO₃ ⁻-containing solution. The re-introduction of Ca²⁺ induced a large transient pH_i decrease followed by a rapid pH_i increase. The plateau pH_i was slightly lower than that before the re-introduction of Ca²⁺. d τ plot of c. The pH_is for 4 min after re-introduction of Ca²⁺ were used. The τ plot revealed that the pH_i increase following the rapid pH_i decrease consisted of the single component during 1 μM IM stimulation