Relationship between intracellular pH (pHi) and calcium (Cai2+) in avian heart fibroblasts

Measurements of pHi and Cai2+ were made in single isolated avian heart fibroblasts using the fluorescent dyes 2,3-dicyanohydroquinone (DCH) and Indo-1. The resting level of Cai2+ is in part maintained by an influx of Ca2+ from the external medium. This flux was reduced in the absence of Ca0(2+) or by adding 2 mM LaCl3 or CoCl2 to the bathing medium; however, it was insensitive to calcium channel blockers nifedipine and verapamil. BAPTA (25 microM), a calcium chelator, also reduced Cai2+. Changes in Cai2+ brought about by any of these methods were found to be accompanied by an intracellular acidification. Experiments were carried out altering pHi using trimethylamine, propionate, and ammonium chloride to determine whether pHi could influence Cai2+. It was found that an intracellular acidification induced a fall in Cai2+ and any rise in pHi induced a rise in Cai2+. These results suggest a direct interaction between Cai2+ and pHi. Various models are described which may account for the experimental observations. The findings are discussed in terms of the possible roles for pHi and Cai2+ and their interactions to influence cell motility and adhesion.