Key result
NOS1 inhibition or knockout in cardiac myocytes leads to decreased contraction and slowed intracellular Ca2+ decline, an effect that is absent in phospholamban knockout myocytes.
NOS1 signaling modulates cardiac contractility and calcium decline by targeting phospholamban serine16 phosphorylation, partially via peroxynitrite.
Should not yet change clinical practice; leaves open NOS1-phospholamban signaling as a contractility target pending in vivo and human validation.
Studies have shown that neuronal nitric oxide synthase (nNOS, NOS1) knockout mice (NOS1-/-) have increased or decreased contractility, but consistently have found a slowed rate of intracellular Ca2+ ([Ca2+]i) decline and relengthening. Contraction and [Ca2+]i decline are determined by many factors, one of which is phospholamban (PLB). The purpose of this study is to determine the involvement of PLB in the NOS1-mediated effects. Force-frequency experiments were performed in trabeculae isolated from NOS1-/- and wild-type (WT) mice. We also simultaneously measured Ca2+ transients (Fluo-4) and cell shortening (edge detection) in myocytes isolated from WT, NOS1-/-, and PLB-/- mice. NOS1-/- trabeculae had a blunted force-frequency response and prolonged relaxation. We observed similar effects in myocytes with NOS1 knockout or specific NOS1 inhibition with S-methyl-l-thiocitrulline (SMLT) in WT myocytes (i.e., decreased Ca2+ transient and cell shortening amplitudes and prolonged decline of [Ca2+]i). Alternatively, NOS1 inhibition with SMLT in PLB-/- myocytes had no effect. Acute inhibition of NOS1 with SMLT in WT myocytes also decreased basal PLB serine16 phosphorylation. Furthermore, there was a decreased SR Ca2+ load with NOS1 knockout or inhibition, which is consistent with the negative contractile effects. Perfusion with FeTPPS (peroxynitrite decomposition catalyst) mimicked the effects of NOS1 knockout or inhibition. beta-Adrenergic stimulation restored the slowed [Ca2+]i decline in NOS1-/- myocytes, but a blunted contraction remained, suggesting additional protein target(s). In summary, NOS1 inhibition or knockout leads to decreased contraction and slowed [Ca2+]i decline, and this effect is absent in PLB-/- myocytes. Thus NOS1 signaling modulates PLB serine16 phosphorylation, in part, via peroxynitrite.
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Wang et al. (2008) studied this question. NOS1 knockout or inhibition vs. Wild-type (WT) mice / myocytes without inhibition was evaluated on Force-frequency response, Ca2+ transient, cell shortening, and [Ca2+]i decline. NOS1 inhibition or knockout in cardiac myocytes leads to decreased contraction and slowed intracellular Ca2+ decline, an effect that is absent in phospholamban knockout myocytes.
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