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 (E_m). In another series, Ca²⁺]_i was measured with Indo-1/AM, dissolved in DMSO. Normoxic cells had a mean E_m of −42.4 mV and Ca²⁺]_i was about 80 nM (measured with both methods). The calculated calcium equilibrium potential (E_Ca) 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 ΔE_m and ΔCa²⁺]_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.