Myofilament Ca2+ desensitization mediates positive lusitropic effect of neuronal nitric oxide synthase in left ventricular myocytes from murine hypertensive heart

Abstract

Neuronal nitric oxide synthase (NOS1 or nNOS) exerts negative inotropic and positive lusitropic effects through Ca(2+) handling processes in cardiac myocytes from healthy hearts. However, underlying mechanisms of NOS1 in diseased hearts remain unclear. The present study aims to investigate this question in angiotensin II (Ang II)-induced hypertensive rat hearts (HP). Our results showed that the systolic function of left ventricle (LV) was reduced and diastolic function was unaltered (echocardiographic assessment) in HP compared to those in shams. In isolated LV myocytes, contraction was unchanged but peak [Ca(2+)]i transient was increased in HP. Concomitantly, relaxation and time constant of [Ca(2+)]i decay (tau) were faster and the phosphorylated fraction of phospholamban (PLN-Ser(16)/PLN) was greater. NOS1 protein expression and activity were increased in LV myocyte homogenates from HP. Surprisingly, inhibition of NOS1 did not affect contraction but reduced peak [Ca(2+)]i transient; prevented faster relaxation without affecting the tau of [Ca(2+)]i transient or PLN-Ser(16)/PLN in HP, suggesting myofilament Ca(2+) desensitization by NOS1. Indeed, relaxation phase of the sarcomere length-[Ca(2+)]i relationship of LV myocytes shifted to the right and increased [Ca(2+)]i for 50% of sarcomere shortening (EC50) in HP. Phosphorylations of cardiac myosin binding protein-C (cMyBP-C(282) and cMyBP-C(273)) were increased and cardiac troponin I (cTnI(23/24)) was reduced in HP. Importantly, NOS1 or PKG inhibition reduced cMyBP-C(273) and cTnI(23/24) and reversed myofilament Ca(2+) sensitivity. These results reveal that NOS1 is up-regulated in LV myocytes from HP and exerts positive lusitropic effect by modulating myofilament Ca(2+) sensitivity through phosphorylation of key regulators in sarcomere.

Neuronal nitric oxide synthase modulation of intracellular Ca2+ handling overrides fatty acid potentiation of cardiac inotropy in hypertensive rats

“…1 Although cardiac metabolism and -oxidation may have downregulated in hypertrophy and in heart failure myocardium, it may not be the case in the model of the current study. Our previous reports clearly presented in echocardiography assessment that myocardial contraction was not altered despite pressure-overload in these rats [13]. F-FTHA uptake in both groups.…”

“…In the myocytes from healthy heart, nNOS-derived NO attenuates basal contractility of cardiac myocytes by modulating the activities of L-type Ca 2+ channels (LTCC) in the plasma membrane to reduce the amplitude of [Ca 2+ ] i transient or promoting Ca 2+ decline by increasing phospholamban phosphorylation [26,34]. Recently, we have shown that nNOS protein expression and activity are up-regulated in left ventricular (LV) myocytes from hypertensive rat hearts whereas endothelial NOS (eNOS) protein expression is reduced [13]. nNOS facilitated myocardial lusitropy by reducing myofilament Ca 2+ sensitivity; myofilament Ca 2+ desensitization, in turn, increased Ca 2+ handling [13,33].…”

“…Recently, we have shown that nNOS protein expression and activity are up-regulated in left ventricular (LV) myocytes from hypertensive rat hearts whereas endothelial NOS (eNOS) protein expression is reduced [13]. nNOS facilitated myocardial lusitropy by reducing myofilament Ca 2+ sensitivity; myofilament Ca 2+ desensitization, in turn, increased Ca 2+ handling [13,33].…”

Afterload-induced diastolic dysfunction contributes to high filling pressures in experimental heart failure with preserved ejection fraction

“…Changes in protein kinase G activity (28), changes in myofilament composition, namely regarding titin, a giant sarcomeric protein that mediates restoring forces and lengthdependent deactivation during the early phase of diastole (12) and that we have shown to be hypophosphorylated in this experimental model (9), as well as disturbances in calcium kinetics (13) may justify disturbed cross-bridge detachment and relaxation kinetics. Relaxation is dependent on both crossbridge detachment and calcium kinetics, and impaired protein kinase G signaling that has been reported in HFpEF patients (28) may be involved not only in titin hypophosphorylation but also in increased calcium sensitivity of the myofilaments and slow cross-bridge detachment (14). Recently, in old hypertensive dogs with HFpEF decreased troponin I, Myosin binding protein C, and myosin light chain 2 hypophosphorylation along with increased calcium sensitivity were also described and related to altered protein kinase activity (10), further supporting changes in regulatory myofilament proteins as a likely molecular explanation for delayed relaxation in HFpEF.…”

Chemokine (C-X-C Motif) Receptor 4 and Atypical Chemokine Receptor 3 Regulate Vascular α1-Adrenergic Receptor Function

“…Left ventricular cardiomyocytes were superfused in 141.4 mmol/L NaCl, 4 mmol/L KCl, 0.33 mmol/L NaH 2 PO4, 1 mmol/L MgCl 2 , 10 mmol/L HEPES, 5.5 mmol/L glucose, 1.8 mmol/L CaCl 2 and 14.5 mmol/L mannitol, pH 7.4, fieldstimulated (20 V, 2 Hz, 6 ms pulse duration) and changes in sarcomere length during contractions after addition of vehicle or various concentrations of CXCR4/ACKR3 ligands (1 nmol/L to 10 μmol/L) measured using a videosarcomere detection system (IonOptix Corp), as described (38,39). Measurements of 60 steady state contractions were averaged for each condition.…”