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1 Servicio de Cardiologia, Hospital Universitari Vall d'Hebron, Barcelona, Barcelona, Spain
* To whom correspondence should be addressed. E-mail: dgdorado{at}hg.vhebron.es.
The effect of simulated ischemia (hypoxia, no glucose, pHo 6.4) on cGMP synthesis induced by stimulation of soluble (sGC) or particulate (pGC) guanylyl cyclase was investigated in adult rat cardiomyocytes. Intracellular cGMP content was measured after stimulation of sGC by S-nitrosopenicillamine (SNAP) or of pGC by natriuretic peptides (urodilatin (URO), atrial (ANP) or C-type (CNP)) for 1 min in the presence of phosphodiesterase inhibitors. After 2 h of simulated ischemia, a decrease of >50% was observed in pGC-dependent cGMP synthesis, but no significant change was observed in sGC-dependent cGMP synthesis. The reduction in cGMP synthesis caused by simulated ischemia was mimicked by extracellular acidosis (pHo 6.4) which decreased pGC- without altering sGC-mediated cGMP synthesis. An extreme sensitivity of pGC activity to low pH was also observed in membrane cell fractions. Hypoxia without acidosis (pHo 7.4) profoundly depressed cellular ATP content, but did not change the response to SNAP, URO or ANP (selective agonists of type A receptor of pGC). Only cGMP synthesis in response to CNP (selective agonist of type B receptor of pGC) was significantly reduced by ATP depletion. These data support the relevance of intracellular pH as a modulator of cGMP, and suggest that in ischemic cardiomyocytes synthesis of cGMP would be mainly NO-dependent.
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