RESPONSE OF CYTOSOLIC CA2+ TO HYPERCAPNIC ACIDOSIS IN CULTURED GLOMUS CELLS OF THE ADULT-RABBIT CAROTID-BODY

The characteristics underlying the response of cytosolic Ca2+ ([Ca2+](i)) to hypercapnic acidosis in clusters of cultured glomus cells of the adult rabbit carotid body were evaluated using fura-2 microscopic fluorometry. Application of CO2 by bubbling through both superfusions of bicarbonate-buffered saline and HEPES-buffered saline produced a rapid and sustained increase in [Ca2+](i). The [Ca2+](i) response increased correspondingly with a rise in concentrations of CO2 to 20% but at a point between 20 and 50% adapted to CO2 and it decreased its linear assent. The hypercapnic acidosis-induced increase of [Ca2+](i) was diminished by removing external Ca2+. Also the [Ca2+](i) response was reduced in dose-dependent fashion by the addition of the voltage-gated Ca2+ channel blocker D600. An additional response of [Ca2+](i) to acetate was also diminished by Ca2+ removal. These results suggest that the [Ca2+](i) response to hypercapnic acidosis involves an influx of external Ca2+ through voltage-gated Ca2+ channels.