Dependence of cellular energy metabolism on the intracellular pH of isolated rabbit parietal cells

Abstract

The cellular energy metabolism under various extracellular pH (pHe) was investigated in parietal cells isolated from rabbit gastric mucosae. Activity of parietal cells was checked by measuring effects of histamine and db-cAMP on the accumulation of aminopyrine in the intracellular canaliculi. The relationship between the intracellular pH (pHi) and pHe was determined by using a fluorescence probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) in suspensions of isolated parietal cell. The pHi was a linear function of pHe and it changed by 0.63 pH unit per 1.0 unit change in pHe. The internal [H+] was equal to the external [H+] at approximately pH 7.0. The respiratory rate of the cell depended on pHi. Values of [ATP] + [ADP] and intracellular inorganic phosphoric acid [Pi] were almost independent of pHi, whereas the [ATP]/[ADP] ratio decreased with increase in pHi. In addition, the standard free energy of ATP(delta Go'ATP) decreases as pHi increases. The calculated available free energy of ATP, which is the sum of delta Go'ATP and -RTlog[ATP]/([ADP] [Pi]), was independent of pHi in the range from pHi 6.2 to 7.6 and its value was about -11.7 kcal/mol. Furthermore, [ATP], [ADP], and [Pi] in the intracellular space were not affected by the presence of histamine or dibutyryl cAMP in media. It was indicated that the available free energy of ATP did not change in the transformation from resting to acid-secreting states, and the phosphorylation potential might have an important role in control of homeostasis in energy metabolism.