Neuronal nitric oxide synthase regulation of calcium cycling in ventricular cardiomyocytes is independent of Cav1.2 channel modulation under basal conditions

Janine Ebner,Bruno K Podesser,Hannes Todt,Karlheinz Hilber,Michal Cagalinec,Helmut Kubista,Xaver Koenig,Livia C Hool,Henrietta Cserne Szappanos,Attila Kiss,Petra L Szabo

doi:10.1007/s00424-019-02335-7

Abstract

Neuronal nitric oxide synthase (nNOS) is considered a regulator of Cav1.2 L-type Ca2+ channels and downstream Ca2+ cycling in the heart. The commonest view is that nitric oxide (NO), generated by nNOS activity in cardiomyocytes, reduces the currents through Cav1.2 channels. This gives rise to a diminished Ca2+ release from the sarcoplasmic reticulum, and finally reduced contractility. Here, we report that nNOS inhibitor substances significantly increase intracellular Ca2+ transients in ventricular cardiomyocytes derived from adult mouse and rat hearts. This is consistent with an inhibitory effect of nNOS/NO activity on Ca2+ cycling and contractility. Whole cell currents through L-type Ca2+ channels in rodent myocytes, on the other hand, were not substantially affected by the application of various NOS inhibitors, or application of a NO donor substance. Moreover, the presence of NO donors had no effect on the single-channel open probability of purified human Cav1.2 channel protein reconstituted in artificial liposomes. These results indicate that nNOS/NO activity does not directly modify Cav1.2 channel function. We conclude that—against the currently prevailing view—basal Cav1.2 channel activity in ventricular cardiomyocytes is not substantially regulated by nNOS activity and NO. Hence, nNOS/NO inhibition of Ca2+ cycling and contractility occurs independently of direct regulation of Cav1.2 channels by NO.

Highlights

During the plateau phase of the ventricular action potential, Ca2+ influx through Cav1.2 L-type Ca2+ channels into the cytosol of cardiomyocytes elicits Ca2+-induced Ca2+ release from the sarcoplasmic reticulum (SR), which triggers contraction
These results are consistent with the established inhibitory effect of Neuronal nitric oxide synthase (nNOS)/nitric oxide (NO) activity on Ca2+ cycling in ventricular cardiomyocytes
Cells originated from four mouse hearts. d Comparison of Ba2+ current amplitudes in rat ventricular cardiomyocytes in the absence and presence of L-VNIO. ctl and drug-treated cells showed no significant difference (p = 0.90, paired Student’s t test; n = 9 for ctl, 9 for drug-treated, and 7 for wash)

Summary

Introduction

During the plateau phase of the ventricular action potential, Ca2+ influx through Cav1.2 L-type Ca2+ channels into the cytosol of cardiomyocytes elicits Ca2+-induced Ca2+ release from the sarcoplasmic reticulum (SR), which triggers contraction. This process is called excitation-contraction (EC) coupling. Besides upregulation of Cav1.2 activity in response to β-adrenergic signalling, neuronal nitric oxide synthase (nNOS) is considered a regulator of Cav1.2 and downstream Ca2+ cycling in the heart. The most widely accepted view is that nitric oxide (NO), generated by nNOS activity in cardiomyocytes, reduces the currents through Cav1.2 channels This gives rise to a diminished Ca2+ release from the SR, as reflected by a smaller amplitude of intracellular Ca2+

Methods

Results

Conclusion