Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA036

Poster Communications

Calcium/calmodulin-dependent protein kinase II is partly responsible for beta-adrenergic stimulation of slow delayed and inward rectifier potassium currents

N. Szentandrassy2,1, B. Horvath1,4, R. Veress1, D. Baranyai1, B. Kurtán1, D. Kiss1, C. Dienes1, J. Magyar1,3, P. Nánási2,1, T. Bányász1

1. Department of Physiology, University of Debrecen, Debrecen, Hungary. 2. Department of Dental Physiology and Pharmacology, University of Debrecen, Debrecen, Hungary. 3. Division of Sport Physiology, Department of Physiology, University of Debrecen, Debrecen, Hungary. 4. Faculty of Pharmacy, University of Debrecen, Debrecen, Hungary.

Introduction and aim: During acute β-adrenergic receptor (β-AR) stimulation the ventricular action potential (AP) shortens by a robust increase of cardiac potassium currents. Besides the well-established protein kinase A pathway, some of the downstream effects of β-AR stimulation are mediated by calcium/calmodulin-dependent protein kinase II (CaMKII). Our aim was to investigate the extent of CaMKII involvement in mediating the effect of β-AR activation on the most important potassium currents flowing during canine ventricular AP. Methods: Experiments were performed on canine left ventricular cardiomyocytes produced by enzymatic digestion using the segment perfusion technique. Adult mongrel dogs were anesthetized with I.M. injections of 10 mg/kg ketamine + 1 mg/kg xylazine as approved by the local ethical committee. A "canonical" AP was used to stimulate every cell under action potential voltage clamp conditions at 37 C without intracellular calcium buffering. Rapid delayed rectifier potassium current (IKr), slow delayed rectifier potassium current (IKs), transient outward current (Ito) and inward rectifier potassium current (IK1) were measured in this order by using their specific blockers in a cumulative manner (1 µM E4031, 0.5 µM HMR-1556, 100 µM Chromanol 293-B and 50 µM BaCl2, respectively). Data were collected in four study groups: Tyrode solution (CTRL), after beta-adrenergic stimulation with 10 nM isoproterenol (ISO), inhibition of CaMKII with 1 µM KN-93 (KN-93), after beta-adrenergic stimulation with inhibited CaMKII (KN-93+ISO). Results: Neither Ito nor IKr differed significantly in the four groups studied. Moreover, there was no difference in either IKs or IK1 among CTRL and KN-93 group. On the contrary, IKs amplitude and total charge were larger in ISO than in CTRL or in KN-93 conditions by about 6- and 8-fold, respectively. In the KN-93+ISO group, IKs showed an about 2.5 times smaller amplitude and carried roughly half as much total charge compared to the ISO group. The total charge carried by IK1 in the ISO group was 25% and 15% larger compared to CTRL and to KN-93+ISO group, respectively. Under beta-adrenergic stimulation, IK1 starts to activate earlier during the AP plateau. IK1 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, IK1 density was about 60% and 90% larger at +20 mV and at 0 mV, respectively, in KN-93+ISO compared to KN-93. Conclusion: CaMKII activation plays an important role in beta-adrenergic stimulation of potassium currents. Part of the beta-adrenergic enhancement of IKs and IK1 is caused by CaMKII activation.

Where applicable, experiments conform with Society ethical requirements