Key Points
- To examine the effects of transient outward potassium current inhibitors on L-type calcium currents and evaluate the molecular mechanisms coupling these channels in ventricular myocytes.
- Measured L-type calcium currents using whole-cell voltage clamp electrophysiology in enzymatically dissociated mouse and guinea pig ventricular myocytes.
- Evaluated the effects of 2 mM 4-aminopyridine in the presence of external calcium or substituted barium, as well as with CaMKII inhibition via 10 μM KN93.
- Application of 2 mM 4-aminopyridine significantly facilitated L-type calcium currents in mouse myocytes by augmenting peak amplitude and slowing inactivation kinetics, an effect that persisted during barium substitution.
- CaMKII activity increased significantly after 4-aminopyridine treatment, while pretreatment with KN93 completely abolished current facilitation.
- In guinea pig myocytes that naturally lack transient outward potassium channels, 4-aminopyridine had no effect on L-type calcium current amplitude or kinetics.
Structured PICO
PPopulationEnzymatically dissociated mouse and guinea pig ventricular myocytes
IInterventionTransient outward current (I(to)) channel blockers: 4-aminopyridine (4-AP) (2 mM) and heteropodatoxin-2 (HpTx2)
CComparatorUntreated cells, and guinea pig ventricular myocytes (which do not express I(to) channels)
OOutcomeL-type calcium current (I(Ca)) amplitude and kineticssurrogate
Inhibition of the transient outward K+ channel facilitates L-type Ca2+ current via CaMKII activation, demonstrating a functional association between these repolarization currents in cardiac myocytes.