Effects of CO2, acetate and lowering extracellular pH on cytosolic Ca2+ and pH in cultured glomus cells of the newborn rabbit carotid body.

Microscopic fluorometry was used to examine the effects of CO2, acetate and low extracellular pH (pHo) on cytosolic Ca2+ ([Ca2+]i, fura-2) and on cytosolic pH (pHi, BCECF) in cultured glomus cells of the newborn rabbit carotid body. Applications of CO2 and acetate at a constant pHo of 7.4 rapidly produced a sustained increase in [Ca2+]i and a sustained decrease in pHi. A slightly lowered pHo of 7.0 slowly induced a small increase in [Ca2+]i and an exponential-like decrease in pHi. An approximately linear correlation was seen between the changed values of [Ca2+]i and pHi induced by the weak acidic stimuli. The speed of the initial pHi response to CO2 was faster than the response to low pHo. It is suggested that the induction of increased [Ca2+]i by hypercapnia and acidosis may be mediated by cytosolic acidification, in which exposure to CO2 causes a faster response than exposure to H+.