HETEROGENEITY IN CYTOSOLIC CALCIUM RESPONSES TO HYPOXIA IN CAROTID-BODY CELLS

Previous investigators have reported that intracellular pH responds to hypoxia with a heterogenous pattern in individual glomus cells of the carotid body. The aim of the present study was to examine whether hyp oxia had similar effects on cytosolic calcium ([Ca2+](i)) in glomus ce lls, and if so, whether a heterogenous response pattern is also seen i n other cell types. Experiments were performed on glomus cells from ad ult rat carotid bodies, rat pheochromocytoma (PC12) and vascular smoot h muscle (A7r5) cells. Changes in [Ca2+](i) in individual cells were d etermined by fluorescence imaging using Fura-2. Glomus cells were iden tified by catecholamine fluorescence. [Ca2+](i) in glomus cells increa sed in response to hypoxia (pO(2) = 35 +/- 8 mmHg; 5 min), whereas hyp oxia induced decreases in [Ca2+](i) were not seen. Increases in [Ca2+] (i) were observed in 20% of the isolated cells and strings of cells, b ut clustered glomus cells never responded. The magnitude of the calciu m change in responding cells was proportional to the hypoxic stimulus. Under a given hypoxic challenge, there were marked variations in the response pattern between glomus cells. The response pattern characteri stic of any given cell was reproducible. At comparable levels of hypox ia, PC12 cells also responded with an increase in [Ca2+](i) with a het erogenous response pattern similar to that seen in glomus cells. In co ntrast, increases in [Ca2+](i) in A7r5 cells could be seen only with s ustained hypoxia (similar to 20 min), and little heterogeneity in the response patterns was evident. These results demonstrate that: (a) hyp oxia increases cytosolic calcium in glomus cells; (b) response pattern s were heterogeneous in individual cells; and (c) the pattern of the h ypoxia-induced changes in [Ca2+](i) is cell specific. These results su ggest that hypoxia-induced increases in [Ca2+](i) are faster in secret ory than in non-secretory cells.