Effect of pH on intracellular free Mg2+ in isolated adult rat cardiomyocytes.

Changes in intracellular pH (pHi) alters the cytosolic concentrations of many electrolytes including Ca2+ and Na+. The present studies determined the effect of pHi on intracellular Mg2+ ([Mg2+]i) activity in isolated adult rat ventricular myocytes. Intracellular magnesium, [Mg2+]i, and calcium, [Ca2+]i, concentrations were measured with microfluorometry. Basal intracellular [Mg2+]i was 634 +/- 27 microM, n = 42 cells, and was not changed following electrical stimulation (0.5 Hz/s) which resulted in transient increases in [Ca2+]i and cell contractions. An NH4Cl pulse was used to rapidly alkalize and acidify the cytosol. Intracellular Mg2+ concentration within single cells decreased by 129 +/- 13 microM with rapid alkalinization of pH from basal levels of 7.1 to 7.6 following a NH4+ pulse. Removal of NH4Cl bathing solution resulted in cytosolic acidification, pH 6.9, and an increase in [Mg2+]i, from 467 +/- 47 to 569 +/- 41 microM. Intracellular [Ca2+] rose with acidification 80 +/- 4 to 149 +/- 19 nM, n = 5, and returned to normal levels, 89 +/- 5 nM, following recovery of pHi. Intracellular acidosis following exposure to 5% CO2/20 mM HCO3- solutions resulted in a significant increase in [Mg2+]i, to 778 +/- 63 microM. These results indicate that intracellular pH may have significant effects on [Mg2+]i in adult cardiomyocytes.