Intracellular pH

About: Intracellular pH is a research topic. Over the lifetime, 8066 publications have been published within this topic receiving 337175 citations.

Calcium homeostasis in intact lymphocytes: cytoplasmic free calcium monitored with a new, intracellularly trapped fluorescent indicator.

Abstract: A new, fluorescent, highly selective Ca2+ indicator , "quin2", has been trapped inside intact mouse and pig lymphocytes, to measure and manipulate cytoplasmic free Ca2+ concentrations, [Ca2+]i. Quin2 is a tetracarboxylic acid which binds Ca2+ with 1:1 stoichiometry and an effective dissociation constant of 115 nM in a cationic background mimicking cytoplasm. Its fluorescence signal (excitation 339 nm, emission 492 nm) increases about fivefold going from Ca-free to CA-saturated forms. Cells are loaded with quin2 by incubation with its acetoxymethyl ester, which readily permeates the membrane and is hydrolyzed in the cytoplasm, thus trapping the impermeant quin2 there. The intracellular quin2 appears to be free in cytoplasm, not bound to membranes and not sequestered inside organelles. The fluorescence signal from resting cells indicates a [Ca2+]i of near 120 nM. The millimolar loadings of quin2 needed for accurately calibrated signals do not seem to perturb steady-state [Ca2+]i, but do somewhat slow or blunt [Ca2+]i transients. Loadings of up to 2mM are without serious toxic effects, though above this level some lowering of cellular ATP is observed. [Ca2+]i was well stabilized in the face of large changes in external Ca2+. Alterations of Na+ gradients, membrane potential, or intracellular pH had little effect. Mitochondrial poisons produced a small increase in [Ca2+]i, probably due mostly to the effects of severe ATP depletion on the plasma membrane. Thus intracellulary trapped chelators like quin2 offer a method to measure or buffer [Ca2+]i in hitherto intractable cell types.

Sensors and regulators of intracellular pH

Abstract: Protons dictate the charge and structure of macromolecules and are used as energy currency by eukaryotic cells. The unique function of individual organelles therefore depends on the establishment and stringent maintenance of a distinct pH. This, in turn, requires a means to sense the prevailing pH and to respond to deviations from the norm with effective mechanisms to transport, produce or consume proton equivalents. A dynamic, finely tuned balance between proton-extruding and proton-importing processes underlies pH homeostasis not only in the cytosol, but in other cellular compartments as well.

Acid pH in Tumors and Its Potential for Therapeutic Exploitation

Abstract: Measurement of pH in tissue has shown that the microenvironment in tumors is generally more acidic than in normal tissues. Major mechanisms which lead to tumor acidity probably include the production of lactic acid and hydrolysis of ATP in hypoxic regions of tumors. Further reduction in pH may be achieved in some tumors by administration of glucose (+/- insulin) and by drugs such as hydralazine which modify the relative blood flow to tumors and normal tissues. Cells have evolved mechanisms for regulating their intracellular pH. The amiloride-sensitive Na+/H+ antiport and the DIDS-sensitive Na+-dependent HCO3-/Cl- exchanger appear to be the major mechanisms for regulating pHi under conditions of acid loading, although additional mechanisms may contribute to acid extrusion. Mitogen-induced initiation of proliferation in some cells is preceded by cytoplasmic alkalinization, usually triggered by stimulation of Na+/H+ exchange; proliferation of other cells can be induced without prior alkalinization. Mutant cells which lack Na+/H+ exchange activity have reduced or absent ability to generate solid tumors; a plausible explanation is the failure of such mutant cells to withstand acidic conditions that are generated during tumor growth. Studies in tissue culture have demonstrated that the combination of hypoxia and acid pHe is toxic to mammalian cells, whereas short exposures to either factor alone are not very toxic. This interaction may contribute to cell death and necrosis in solid tumors. Acidic pH may influence the outcome of tumor therapy. There are rather small effects of pHe on the response of cells to ionizing radiation but acute exposure to acid pHe causes a marked increase in response to hyperthermia; this effect is decreased in cells that are adapted to low pHe. Acidity may have varying effects on the response of cells to conventional anticancer drugs. Ionophores such as nigericin or CCCP cause acid loading of cells in culture and are toxic only at low pHc; this toxicity is enhanced by agents such as amiloride or DIDS which impair mechanisms involved in regulation of pHi. It is suggested that acid conditions in tumors might allow the development of new and relatively specific types of therapy which are directed against mechanisms which regulate pHi under acid conditions.