Calcium/calmodulin-dependent protein kinase II stimulates the inward rectifier potassium current in beta-adrenergic adaptation of ventricular cardiomyocytes

Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): NEW NATIONAL EXCELLENCE PROGRAM OF THE MINISTRY FOR INNOVATION AND TECHNOLOGY FROM THE SOURCE OF THE NATIONAL RESEARCH, DEVELOPMENT AND INNOVATION FUND. Introduction and purpose Acute β-adrenergic receptor (β-AR) stimulation shortens the ventricular action potential (AP). This effect is mainly regulated by the β- adrenergic stimulation of the cardiac potassium currents. Our aim was to investigate the extent of calcium/calmodulin-dependent protein kinase II (CaMKII) involvement in mediating the effect of β-AR activation on the inward rectifier potassium current – I K1 . Methods We carried out our experiments on isolated cardiomyocytes originating from canine left ventricles. The inward rectifier potassium current – I K1 was measured under a "canonical" AP under action potential voltage clamp conditions. Data were collected in four study groups [1] Control conditions (CTRL) [2] Inhibition of CaMKII with 1 µM KN-93 (KN-93) [3] Inhibition of PKA with 3 µM H-89 (H-89) [4] Acute β-adrenergic stimulation with 10 nM isoproterenol (ISO) [5] β-adrenergic stimulation with CaMKII inhibition (KN-93 + ISO) [6] β-adrenergic stimulation with PKA inhibition (H-89 + ISO) [7] β-adrenergic stimulation with inhibited PKA and CaMKII (KN-93 + H-89 + ISO) Results I K1 current amplitude did not differ among the studied groups, the total carried charge however was significantly, about 30 % larger in the ISO group compared to CTRL, and about 20 % larger compared to KN-93 + ISO. Under beta- adrenergic stimulation, I K1 starts to activate earlier during the AP plateau. I K1 density was about 3 times greater both at +20 mV and at 0 mV membrane potential under the command "canonical" AP in ISO compared to CTRL. Similarly, I K1 density was about 60 % and 90 % larger at +20 mV and at 0 mV, respectively, in KN-93 + ISO compared to KN-93. Similar results have been obtained by conventional voltage-clamp technique. Conclusion Based on the results of our researches the CaMKII activation plays an important role in β -adrenergic stimulation the I K1 potassium current.