Effects of hypoxia induced by Na2S2O4 on intracellular calcium and resting potential of mouse glomus cells

Isolated and cultured glomus cells, obtained from mouse carotid bodies, were superfused with Ham's F-12 equilibrated with air (mean PO2, 119 Torr; altitude 1350 m). [Ca2+]o was 3.0 mM. In one experimental series, dual cell penetrations with microelectrodes measured intracellular calcium ([Ca2+]i) and the resting potential (Em). In another series, [Ca2+]i was measured with Indo-1/AM, dissolved in DMSO. Normoxic cells had a mean Em of -42.4 mV and [Ca2+]i was about 80 nM (measured with both methods). The calculated calcium equilibrium potential (ECa) was 137+/-0.74 mV. Hypoxia, induced by Na2S2O4 1 mM, reduced pO2 to 10-14 Torr. This effect was accompanied by cell depolarization to -19.1 mV. Hypoxia increased [Ca2+]i to 231 nM when detected with Ca-sensitive microelectrodes, but only to 130.2 nM when measured with Indo-1/AM. Calcium increases were preceded by decreases in [Ca2+]i, which also were more pronounced with microelectrode measurements. CoCl2 1 mM blocked the hypoxic [Ca2+]i increase and exaggerated the decreases in [Ca2+]i. Correlations between DeltaEm and Delta[Ca2+]i during hypoxia were significant (p<0.05) in 19% of the cells. But, in 29% of them significance was at the p<0.1 level. In the rest (52%), there was no correlation between these parameters. Thus, voltage-gated calcium channels are rare in mouse glomus cells. Their activation by depolarization cannot explain the two to threefold increase in [Ca2+]i seen during hypoxia. More likely, [Ca2+]i increase may be due to hypoxic inactivation of a Ca-Mg ATPase transport system across the cell membrane. The blunting of hypoxic [Ca2+]i increase, seen in Indo-1/AM experiments, is probably due to its solvent (DMSO), which also depresses hypoxic cell depolarization.