Figure 2.

Addition of constitutively active CaMK reconstitutes I_Ca facilitation and reciprocally reduces release of Ca²⁺ from intracellular stores. (a) I_Ca facilitation is absent in this cell dialyzed with buffer solution (Buffer Control), but is present after addition of constitutively active CaMK (CaMK). Numerals indicate the beat number as in Fig. 1, and the calibration bars represent 500 pA (vertical) and 100 ms (horizontal). (b) Averaged intracellular Ca²⁺ transients using the fluorescent indicator fluo 3 (see Methods), for beats 1–10 to show the sustained reduction in Ca²⁺ release from intracellular stores by CaMK (n = 5) compared with buffer alone (n = 5). (c) Summary of data showing I_Ca facilitation expressed as the ratio of peak I_Ca during the first to the nth beat [I_Ca(n)], as shown in Fig. 1. I_Ca facilitation was significantly increased by CaMK (n = 5) compared with control (P < 0.05 for beats 2 and 4–10, n = 5). (d) Peak fluo 3 fluorescence signals for each stimulated beat, measured simultaneously with I_Ca reported in c. CaMK significantly reduced peak fluo 3 fluorescence compared with control (P < 0.05 for beats 3, 5, 8–10).