Coupling of angiotensin II AT1 receptors to neuronal NHE activity and carrier-mediated norepinephrine release in myocardial ischemia.
In ischemia, cardiac sympathetic nerve endings (cSNE) release excessive amounts of norepinephrine (NE) via the nonexocytotic Na(+)-dependent NE transporter (NET). NET, normally responsible for NE reuptake into cSNE, reverses in myocardial ischemia, releasing pathological amounts of NE. This carrier-mediated NE release can be triggered by elevated intracellular Na(+) levels in the axoplasm. The fact that ischemia activates the intracellular pH regulatory Na(+)/H(+) exchanger (NHE) in cSNE is pivotal in increasing intraneuronal Na(+) and thus activating carrier-mediated NE release. Angiotensin (ANG) II levels are also significantly elevated in the ischemic heart. However, the effects of ANG II on cSNE, which express the ANG II receptor, AT(1)R, are poorly understood. We hypothesized that ANG II-induced AT(1)R activation in cSNE may be positively coupled to NHE activity and thereby facilitate the pathological release of NE associated with myocardial ischemia. We tested this hypothesis in a cSNE model, human neuroblastoma cells stably transfected with rat recombinant AT(1A) receptor (SH-SY5Y-AT(1A)). SH-SY5Y-AT(1A) constitutively expresses amiloride-sensitive NHE and the NET. NHE activity was assayed in BCECF-loaded SH-SY5Y-AT(1A) as the rate of the Na(+)-dependent alkalinization in response to an acute acidosis. ANG II activation of AT(1)R markedly increased NHE activity in SH-SY5Y-AT(1A) via a Ca(2+)-dependent pathway and promoted carrier-mediated NE release. In addition, in guinea pig cSNE expressing native AT(1)R, ANG II elicited carrier-mediated NE release. In SH-SY5Y-AT(1A) and cSNE, amiloride inhibited the ANG II-mediated release of NE. Our results provide a link between AT(1)R and NHE in cSNE, which can exacerbate carrier-mediated NE release during protracted myocardial ischemia.
Reid
Alicia C
AC
Department of Physiology and Biophysics, Cornell University, Weill Cornell Medical College, New York, NY 10021, USA.
Mackins
Christina J
CJ
Seyedi
Nahid
N
Levi
Roberto
R
Silver
Randi B
RB
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D020013:Calcium Signaling / Q000502:physiology; D002460:Cell Line; D006168:Guinea Pigs; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D017202:Myocardial Ischemia / Q000378:metabolism*; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000201:enzymology*; D009638:Norepinephrine / Q000378:metabolism*; D050484:Norepinephrine Plasma Membrane Transport Proteins; D011726:Pyridinium Compounds / Q000494:pharmacology; D044140:Receptor, Angiotensin, Type 1 / Q000187:drug effects / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000502:physiology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism; D027981:Symporters / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism
D007527:Isoenzymes; D050484:Norepinephrine Plasma Membrane Transport Proteins; D011726:Pyridinium Compounds; D044140:Receptor, Angiotensin, Type 1; C493227:SLC6A2 protein, human; D017923:Sodium-Hydrogen Exchangers; D027981:Symporters; D000804:Angiotensin II; C026560:1-(4-methoxyphenyl)pyridinium; D012964:Sodium; D009638:Norepinephrine