Beta-Adrenergic Activation of the Inward Rectifier K+ Current Is Mediated by the CaMKII Pathway in Canine Ventricular Cardiomyocytes

Figures

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  Figure 1. (A) Command action potential and (B) representative IK1 current traces obtained under APVC conditions in untreated control cells (CTRL), with ß-adrenergic stimulation in the presence of 10 nM ISO (ISO), ß-adrenergic stimulation following CaMKII inhibition with 1 µM KN-93 (KN-93 + ISO), ß-adrenergic stimulation following PKA inhibition with 3 µM H-89 (H-89 + ISO), and ß-adrenergic stimulation with the inhibition of both kinases (KN-93 + H-89 + ISO).

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  Figure 2. The effect of ß-adrenergic stimulation on IK1 and the suppressibility of this effect by CaMKII inhibition (KN-93) and PKA inhibition (H-89). Data obtained in 5 groups of myocytes are compared: untreated control (CTRL; n = 7/5), ß-adrenergic stimulation alone (ISO; n = 7/6), ß-adrenergic stimulation following CaMKII inhibition (KN-93 + ISO; n = 7/6), ß-adrenergic stimulation following PKA inhibition (H-89 + ISO; n = 10/7), and ß-adrenergic stimulation with the inhibition of both kinases (KN-93 + H-89 + ISO; n = 9/7). The “n” numbers in parentheses indicate the number of cells over the number of animals used in that experimental group. (A) Mid-plateau current densities, (B) peak current densities, (C) current integrals. Symbols and bars are mean ± SEM, and small dots represent individual data. Asterisks (*) indicate significant differences (p < 0.05) between groups. NS: not significant.

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  Figure 3. (A) Command action potential (above) and representative enlarged IK1 current traces flowing during the action potential plateau (below). Dashed lines indicate the corresponding voltage and current values at 0 mV and at +20 mV. (B,C) IK1 densities measured at +20 mV and at 0 mV, respectively, in the 5 cell groups of control (CTRL; n = 7/5), ß-adrenergic stimulation alone (ISO; n = 7/6), ß-adrenergic stimulation following CaMKII inhibition (KN-93 + ISO; n = 7/6), ß-adrenergic stimulation following PKA inhibition (H-89 + ISO; n = 10/7), and ß-adrenergic stimulation with the inhibition of both kinases (KN-93 + H-89 + ISO; n = 9/7). The “n” numbers in parentheses indicate the number of cells over the number of animals used in that experimental group. Symbols and bars are mean ± SEM, and small dots represent individual data. Asterisks (*) indicate significant differences (p < 0.05) between groups. NS: not significant.

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  Figure 4. The effects of ISO alone and in the presence of KN-93 and H-89 on the IK1 density under conventional voltage clamp conditions. (A) IK1 densities measured at the end of various test potentials (shown on the abscissa) lasting for 250 ms and rising from the holding potential of −80 mV in the 4 cell groups of control (CTRL; n = 11/3), ß-adrenergic stimulation alone (ISO; n = 9/5), ß-adrenergic stimulation following CaMKII inhibition (KN-93 + ISO; n = 10/3), and ß-adrenergic stimulation following PKA inhibition (H-89 + ISO; n = 9/5). The “n” numbers in parentheses indicate the number of cells over the number of animals used in that experimental group. Detailed statistical analyses of the IK1 densities measured at −20 mV and 0 mV are depicted in panels (B) and (C), respectively. Symbols and bars are mean ± SEM, and small dots represent individual data. On panel (A), daggers (†) and hash signs (#) indicate significant differences (p < 0.05) between the control and ISO groups and between the ISO and KN-93 + ISO groups, respectively. On panels (B,C), asterisks (*) indicate significant differences (p < 0.05) between groups. NS: not significant.

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  Figure 5. CaMKII inhibition with KN-93 or PKA inhibition with H-89 has no effect on IK1 under baseline conditions. The cell groups of control (CTRL; n = 7/5), CaMKII inhibition (KN-93; n = 8/5), and PKA inhibition (H-89; n = 7/4) were compared. The “n” numbers in parentheses indicate the number of cells over the number of animals used in that experimental group. (A) Command action potential (above) and the corresponding representative IK1 current traces flowing during the action potential (below). (B) Mid-plateau current densities, (C) peak current densities, and (D) current integrals. Symbols and bars are mean ± SEM, and small dots represent individual data. The arithmetic means of the groups were not significantly different in any parameters with one-way ANOVA.

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  Figure 6. The effects of PKA and CaMKII inhibition with or without ß -adrenergic receptor activation on IKr. The cell groups of control (CTRL; n = 7/5), CaMKII inhibition under baseline conditions (KN-93; n = 9/5), PKA inhibition under baseline conditions (H-89; n = 7/4), ß-adrenergic stimulation alone (ISO; n = 7/6), ß-adrenergic stimulation following CaMKII inhibition (KN-93 + ISO; n = 11/6), and ß-adrenergic stimulation following PKA inhibition (H-89 + ISO; n = 8/6). The “n” numbers in parentheses indicate the number of cells over the number of animals used in that experimental group. (A) Command action potential (above) and the corresponding representative IKr current profiles flowing during the action potential (below). (B) Mid-plateau current densities, (C) peak current densities, and (D) current integrals. Symbols and bars are mean ± SEM, and small dots represent individual data. The arithmetic means of the groups were not significantly different in any parameters with one-way ANOVA.