Acute pH sensitivity of Ca²⁺ current and CaT unaffected by CaMKII inhibition (rabbit myocytes). The normal pipette filling solution (no BAPTA) was used in all voltage-clamp experiments shown in this figure. (A) 1 µM KN-93 reduced I_Ca,L under control conditions (pH_o 7.4): control, n = 26; KN-93, n = 8. The voltage-clamp protocol used for the KN-93 experiments was identical to that used to generate the results in Fig. 4 (CL = 5 s). (B) In the presence of 1 µM KN-93, intracellular acidosis shifted the I-V curve to the left (red arrow), with no change in the peak (n = 8), the same response observed without KN-93 (compare Fig. 4 B, left). (C) Summarized effects of intracellular acidosis (2 min) on CaT characteristics in the presence (n = 5) and absence (n = 12) of 1 µM KN-93, expressed as percent change. Cells were field stimulated at CL = 2 s. There was no significant difference between the two groups (unpaired). Inset shows example CaTs from a myocyte in KN-93 during control and after 2 min of intracellular acidosis. (D) Effect of combined acidosis on I_Ca,L in the presence of 1 µM KN-93 (n = 8). The response to combined acidosis was very similar to that without KN-93 (compare Fig. 4 C, left).