An essential regulator of cardiac contractility is ?-adrenergic receptor (?AR) signaling. (?1 and ?2 receptors are the primary subtypes expressed in the heart. ?1 receptors produce positive inotropic and lusitropic effects through modulation of the L-type Ca2+ channel, phospholamban (PLB) and troponin I (Tnl). ?2 receptors are unique in that they only function as positive inotropes;these receptors promote contractility through regulation of the L-type Ca2+ channel. ?AR signaling itself can be regulated by nitric oxide (NO) produced via NO synthase (NOS). Within the myocyte, two NOS isoforms are constitutively expressed: NOS1 and NOS3. NOS1 signaling has been shown to augment the functional response to non-specific ?AR stimulation while NOS3 signaling reduces it. However, it remains to be determined what effect specific NOS isoforms have in the regulation of individual ?AR receptors. Interestingly, NOS1 and ?1 receptors have been shown to regulate contractility via similar protein targets (i.e.PLB), while NOS3 and ?2 receptors regulate contractility through the L-type Ca2+ channel. Recently, NOS3 and ?2 receptors have been shown to compartmentalize to similar locations within the myocyte. Therefore, we hypothesize NOS1 will increase the functional response due to ?1 receptor activation with no modulation of ?2 receptor signaling (Aim1). In addition, we hypothesize NOS3 will decrease the functional response due to ?2 receptor activation with no modulation of ?1 receptor signaling (Aim2). Functional experiments (i.e. measurement of Ca2+ transient, shortening amplitude, and L-type Ca2+channel current) and western blotting (PLB-phosphorylation) to investigate this proposed functional interaction will be conducted in isolated myocytes from wild type (WT, control), NOS1 knockout (KO) and NOS3 KO mice exposed to various ?AR stimuli. Our study holds health-relatedness due to the fact that when ?AR signaling is altered, this signaling pathway promotes contractile dysfunction and cardiac remodeling. Thus, it is crucial to determine how ?AR signaling is regulated. With a deeper understanding of this phenomena, our study will make possible the development of new therapeutic treatments.
| Traynham, Christopher J; Roof, Steve R; Wang, Honglan et al. (2012) Diesterified nitrone rescues nitroso-redox levels and increases myocyte contraction via increased SR Ca(2+) handling. PLoS One 7:e52005 |
