Abstract
The Na+/H+ antiport and Na(+)-HCO3- coinflux carrier contribute to recovery from intracellular acidosis in cardiac tissue. The effects of angiotensin II (10(-12)-10(-6) M) on H+ fluxes after intracellular acid loading and during reperfusion after myocardial ischemia have been investigated in the isovolumic, Langendorff-perfused ferret heart. Intracellular pH (pHi) was estimated using 31P nuclear magnetic resonance (NMR) spectroscopy from the chemical shift of intracellular deoxyglucose-6-phosphate or inorganic phosphate. Angiotensin II produced concentration-dependent stimulation (maximum at 10(-6) M: 67%) of 5-(N-ethyl-N-isopropyl)amiloride (EIPA)-sensitive Na(+)-dependent of H+ efflux consistent with stimulation of the Na+/H+ antiport. Half-maximal stimulation of H+ efflux occurred at approximately 10(-9) M, which is close to the dissociation constant of the cardiac angiotensin AT1 receptor. Stimulation via this receptor was confirmed with the nonpeptide AT1 receptor blocker, GR-117289. Angiotensin II had less pronounced effects on HCO3(-)-dependent pHi recovery after acid loading with no effect on pHi recovery after intracellular alkalosis. During reperfusion, angiotensin II significantly increased H+ extrusion but impaired contractile recovery. The results support the hypothesis that angiotensin II facilitates H+ extrusion in the heart. This may help maintain physiological homeostasis, but the hypothesized obligated Na+ influx could exacerbate cellular dysfunction during reperfusion.
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