Impaired intracellular calcium homeostasis during acute prolonged severe hypoxia in rat carotid body cells

Abstract

CB glomus cells depolarize in hypoxia, leading to calcium influx. As a first line defense against hypoxia, their response to prolonged, acute hypoxia is important. We studied the effects of 15 min of severe, acute hypoxia. CBs were harvested from 14–17 day rats, dissociated, loaded with fura‐2, and perfused with HCO3‐buffered salt solution (BSS) equilibrated with 21% O2+5% CO2 (normoxia, N), 0% O2+5% CO2 (severe hypoxia, SH), 1–2% O2+5% CO2 (moderate hypoxia, MH) or 20 mM KCl in N. Cells were exposed to 1 min KCl, 2 min SH, 15 minute SH and final 2 min SH, with 5 min recovery in between. Glomus cells were identified by morphology and response to KCl. Results (n>50): 100% of glomus cells exposed 2 min to SH exhibited a brisk rise in intracellular calcium ([Ca2+]i) and returned to baseline upon return to N. 15 min of SH resulted in a brisk rise in [Ca2+]i and decline to a lower steady state, but [Ca2+]i homeostasis was severely impaired, with persistent elevation of [Ca2+]i. Many cells responded again to hypoxia following SH, indicating viability. 15 min exposure to KCl showed a [Ca2+]i response profile nearly identical to 15 min SH, but [Ca2+]i homeostasis remained intact. Impaired [Ca2+]i handling was also observed with MH (PO2 ~ 8–9 mmHg) but much less with mild hypoxia (~ 15–18 mmHg). Preliminary results suggest that prolonged, acute hypoxia markedly impairs [Ca2+]i homeostasis in CB glomus cells, which may have clinical relevance.