Na+-induced Ca2+ influx through reverse mode of Na+-Ca2+ exchanger in mouse ventricular cardiomyocyte
Zhen-Yu Yan1,2, Tao Ban1,3, Yao Fan1
1Department of Pharmacology, Harbin Medical University, Harbin, China.
Background:
Dobutamine is commonly used for clinical management of heart failure and its pharmacological effects have long been investigated as inotropics via β-receptor activation. However, there is no electrophysiological evidence if dobutamine contributes inotropic action due at least partially to the reverse mode of Na+-Ca2+ exchanger (NCX) activation.
Methods:
Action potential (AP), voltage-gated Na+ (INa), Ca2+ (ICa), and K+ (Ito and IK1) currents were observed using whole-cell patch technique before and after dobutamine in ventricular cardiomyocytes isolated from adult mouse hearts. Another sets of observation were also performed with Kb-r7943 or in the solution without [Ca2+]o.
Results:
Dobutamine (0.1-1.0 μM) significantly enhanced the AP depolarization with prolongation of AP duration (APD) in a concentration-dependent fashion. The density of INa was also increased concentration-dependently without alternation of voltage-dependent steady-status of activation and inactivation, reactivation as well. Whereas, the activities for ICa, Ito, and IK1 were not changed by dobutamine. Intriguingly, the dobutamine-mediated changes in AP repolarization were abolished by 3 μM Kb-r7943 pretreatment or by simply removing [Ca2+]o without affecting accelerated depolarization. Additionally, the ratio of APD50/APD90 was not significantly altered in the presence of dobutamine, implying that effective refractory period was remain unchanged.
Conclusions:
This novel finding provides evidence that dobutamine upregulates of voltage-gated Na+ channel function and Na+ influx-induced activation of the reverse mode of NCX, suggesting that dobutamine may not only accelerate ventricular contraction via fast depolarization but also cause Ca2+ influx, which contributes its positive inotropic effect synergistically with β-receptor activation without increasing the arrhythmogenetic risk.
Insights
Dobutamine enhances heart contraction by increasing sodium channel function and activating the Na+-Ca2+ exchanger, contributing to its positive inotropic effect without raising arrhythmia risk.
Area of Science:
- Cardiology
- Electrophysiology
- Pharmacology
Background:
- Dobutamine is a common heart failure treatment acting via beta-receptor activation.
- Its positive inotropic effects are well-known, but the electrophysiological mechanisms are not fully understood.
- The role of the Na+-Ca2+ exchanger (NCX) in dobutamine's action is unclear.
Purpose of the Study:
- To investigate the electrophysiological mechanisms of dobutamine's inotropic action.
- To determine if dobutamine activates the reverse mode of the Na+-Ca2+ exchanger (NCX).
- To assess the impact of dobutamine on cardiac action potentials and ion currents.
Main Methods:
- Whole-cell patch-clamp technique used on adult mouse ventricular cardiomyocytes.
- Measurements of action potential (AP), Na+ current (INa), Ca2+ current (ICa), and K+ currents (Ito, IK1).
- Experiments conducted with and without dobutamine, and with NCX inhibitor (Kb-r7943) or calcium-free solution.
Main Results:
- Dobutamine (0.1-1.0 μM) concentration-dependently enhanced AP depolarization and prolonged AP duration (APD).
- Dobutamine increased INa density but did not alter ICa, Ito, or IK1.
- NCX inhibition or calcium removal abolished dobutamine's AP repolarization effects, while accelerated depolarization remained.
Conclusions:
- Dobutamine upregulates voltage-gated Na+ channels, increasing Na+ influx.
- This Na+ influx activates the reverse mode of the NCX, leading to Ca2+ influx.
- Dobutamine synergistically enhances contraction via fast depolarization and NCX-mediated Ca2+ influx, without increasing arrhythmia risk.
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