Effect of nitric oxide donors S‐nitroso‐N‐acetyl‐dl‐penicillamine, spermine NONOate and propylamine propylamine NONOate on intracellular pH in cardiomyocytes

Previous studies suggest that exogenous nitric oxide (NO) and NO‐dependent signalling pathways modulate intracellular pH (pHi) in different cell types, but the role of NO in pHi regulation in the heart is poorly understood. Therefore, in the present study we investigated the effect of the NO donors S‐nitroso‐N‐acetyl‐dl‐penicillamine, spermine NONOate and propylamine propylamine NONOate on pHi in rat isolated ventricular myocytes. Cells were isolated from the hearts of adult Wistar rats and pHi was monitored using the pH‐sensitive fluorescent indicator 5‐(and‐6)‐carboxy seminaphtharhodafluor (SNARF)‐1 (10 μmol/L) and a confocal microscope. To test the effect of NO donors on the Na+/H+ exchanger (NHE), basal pHi in Na+‐free buffer and pHi recovery from intracellular acidosis after an ammonium chloride (10 mmol/L) prepulse were monitored. The role of carbonic anhydrase was tested using acetazolamide (50 μmol/L). 4,4‐Diisothiocyanatostilbene‐2,2′‐disulphonic acid (0.5 mmol/L; DIDS) was used to inhibit the Cl−/OH− and Cl−/ HCO3− exchangers. Acetazolamide and DIDS were applied via the superfusion system 1 and 5 min before the NO donors. All three NO donors acutely decreased pHi and this effect persisted until the NO donor was removed. In Na+‐free buffer, the decrease in basal pHi was increased, whereas inhibition of carbonic anhydrase and Cl−/OH− and Cl−/ HCO3− exchangers did not alter the effects of the NO donors on pHi. After an ammonium preload, pHi recovery was accelerated in the presence of the NO donors. In conclusion, exogenous NO decreases basal pHi, leading to increased NHE activity. Carbonic anhydrase and chloride‐dependent sarcolemmal HCO3− and OH− transporters are not involved in the NO‐induced decrease in pHi in rat isolated ventricular myocytes.