Acidosis and Ca²⁺ current inactivation kinetics. Effect of acidosis on the voltage dependence of I_Ca,L inactivation kinetics. Cells (rabbit) were voltage clamped according to the protocol shown in Fig. 3 (CL = 5 s). τ_f and τ_s were measured as described in Materials and methods, with all acidic results shown in red. The normal pipette filling solution (no BAPTA) was used in all experiments shown in this figure. (A) Extracellular acidosis (n = 6) had little effect on inactivation kinetics. (B) In contrast, intracellular (n = 14) acidosis slowed both τ_f and τ_s over most of the voltage range. (B) Combined acidosis (n = 6) caused the greatest slowing of inactivation. **, P < 0.01; *, P < 0.05, paired; control compared with 2 min of acidosis. The example records were recorded from three different cells in response to a clamp step from −40 to +20 mV.