Regulation of myocyte contraction via neuronal nitric oxide synthase: role of ryanodine receptor S‐nitrosylation

The sarcoplasmic reticulum (SR) Ca2+ release channel (ryanodine receptor, RyR2) has been proposed to be an end target of neuronal nitric oxide synthase (NOS1) signalling. The purpose of this study is to investigate the mechanism of NOS1 modulation of RyR2 activity and the corresponding effect on myocyte function. Myocytes were isolated from NOS1 knockout (NOS1−/−) and wild‐type mice. NOS1−/− myocytes displayed a decreased fractional SR Ca2+ release, NOS1 knockout also led to reduced RyR2 S‐nitrosylation levels. RyR2 channels from NOS1−/− hearts had decreased RyR2 open probability. Additionally, knockout of NOS1 led to a decrease in [3H]ryanodine binding, Ca2+ spark frequency (CaSpF) and a rightward shift in the SR Ca2+ leak/load relationship. Similar effects were observed with acute inhibition of NOS1. These data are indicative of decreased RyR2 activity in myocytes with NOS1 knockout or acute inhibition. Interestingly, the NO donor and nitrosylating agent SNAP reversed the depressed RyR2 open probability, the reduced CaSpF, and caused a leftward shift in the leak/load relationship in NOS1−/− myocytes. SNAP also normalized Ca2+ transient and cell shortening amplitudes and SR fractional release in myocytes with NOS1 knockout or acute inhibition. Furthermore, SNAP was able to normalize the RyR2 S‐nitrosylation levels. These data suggest that NOS1 signalling increases RyR2 activity via S‐nitrosylation, which contributes to the NOS1‐induced positive inotropic effect. Thus, RyR2 is an important end target of NOS1. Nitric oxide (NO) is an important regulator of cardiac contraction. NO produced via the neuronal isoform of NO synthase (NOS1) leads to enhanced contraction. We show that part of the enhanced contraction via NOS1 is through the modulation of the sarcoplasmic reticulum Ca2+ release channel (ryanodine receptor). Specifically, we find that NOS1 leads to S‐nitrosylation and increased activity of the ryanodine receptor. We further show that the increased ryanodine receptor activity by NOS1 contributes to the enhanced contraction. These results reveal a mechanism of how NOS1 modulates cardiac contraction and helps us understand how NO influences cardiac function.