Effects of pH conditions on Ca2+ transport catalyzed by ionophores A23187, 4-BrA23187, and ionomycin suggest problems with common applications of these compounds in biological systems

Biophysical Journal
W L ErdahlD R Pfeiffer

Abstract

Phospholipid vesicles loaded with Quin-2 and 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) have been used to investigate the effects of pH conditions on Ca2+ transport catalyzed by ionophores A23187, 4-BrA23187, and ionomycin. At an external pH of 7.0, a delta pH (inside basic) of 0.4-0.6 U decreases the rate of Ca2+ transport into the vesicles by severalfold under some conditions. The apparent extent of transport is also decreased. In contrast, raising the pH by 0.4-0.6 U in the absence of a delta pH increases both of these parameters, although by smaller factors. The relatively large effects of a delta pH on the transport properties of Ca2+ ionophores seem to reflect a partial equilibration of the transmembrane ionophore distribution with the H+ concentration gradient across the vesicle membrane. This unequal distribution of ionophore can cause a very slow or incomplete ionophore-dependent equilibration of delta pCa with delta pH. A second factor of less certain origin retards full equilibration of delta pCa when delta pH = 0. These findings call into question several ionophore-based methods that are used to investigate the regulatory activities of Ca2+ and other divalent cations in biological systems. Notable amo...Continue Reading

Citations

Nov 20, 2013·Neuroscience Letters·Daniel TorrenteRubem Carlos Araújo Guedes
Nov 27, 2001·Biophysical Journal·E WangD R Pfeiffer
Sep 27, 2008·Current Protocols in Cell Biology·Herve Barriere, Gergely L Lukacs
Mar 4, 2000·The Journal of Biological Chemistry·W L ErdahlD R Pfeiffer

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