Physical properties of biological membranes determined by the fluorescence of the calcium ionophore A23187 (original) (raw)
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Ca2+ transport mediated by a synthetic neutral Ca2+-ionophore in biological membranes
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1977
The effect of a synthetic neutral ligand on the Ca 2÷ permeability of several biological membranes has been investigated. The ligand had been previously shown to possess Ca2*-ionophoric activities in artificial phospholipid membranes. The neutral ionophore is able to transport Ca 2÷ across the membranes of erythrocytes and sarcoplasmic reticulum, when lipophilic anions such as tetraphenylborate or carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) are present, presumably to facilitate the diffusion of the charged Ca 2÷ionophore complex across the hydrophobic core of the membrane. In mitochondria, the neutral ionophore promotes the active transport of Ca 2÷ in response to the negative membrane potential generated by respiration, in the presence of the specific inhibitor of the natural carrier ruthenium red. Abbreviations used: FCCP, carbonylcyanide p-trifluoromethoxyphenylhydrazone; HEPES, N-2hy droxyethylpiperazine-N'-2-cthanesul fonic acid.
The Journal of Membrane Biology, 1977
The kinetics of the transport of the 1-anilino-8-naphthalenesulfonate (ANS-, an anionic fluorescent probe of the membrane surface) across phospholipid vesicle membranes have been studied using a stopped-flow rapid kinetic technique. The method has been used to gain detailed information about the mechanism of transport of this probe and to study ionophore-mediated cation transport across the membrane. The technique has also been exploited to study differences between the inside and outside surfaces of vesicles containing pbosphatidyl choline (PC).
Ion Transport Across a Bilayer Lipid Membrane in the Presence of a Hydrophobic Ion or an Ionophore
Journal of nuclear and radiochemical sciences, 2005
The ion transport from one aqueous phase (W1) to another (W2) across a bilayer lipid membrane (BLM) in a cell system in the presence of a hydrophobic ion or an ionophore was investigated by voltammetry. The ion transport current was observed by addition of a small amount of hydrophobic ion such as tetraphenylborate, dipicrylaminate, etc. into W1 or/and W2 containing a hydrophilic salt serving as a supporting electrolyte. The hydrophobic ion was distributed into the BLM with the counter ion to hold the electroneutrality within the BLM. It was pointed out that the counter ion could transfer between W1 and W2 across the BLM since concentrations of the counter ion in WI, BLM, and W2 were so high as to cause the ion transfer current while concentrations of the hydrophobic ion were very low. The facilitated transports of alkali ions across a BLM containing valinomycin (Val) used as an ionophore were also investigated by considering the hydrophobicity of both the objective cation and the counter anion and the formation of the alkali metal ion-Val complex.
The Journal of Membrane Biology, 1982
port have, in the main, utilized artificial membranes, both planar and vesicular. Systems of biological interest, viz., cells and organelles, resemble vesicles in size and geometry. Methods are, therefore, required to extend the results obtained with planar membranes to liposome systems. In this report we present an analysis of a fluorescence technique, using the divalent cation probe chlortetracycline, in small, unilamellar vesicles, for the study of divalent cation fluxes. An ion carrier (X537A) and a pore former (alamethicin) have been studied. The rate of rise of fluorescence signal and the transmembrane ion gradient have been related to transmembrane current and potential, respectively. A second power dependence of ion conduction-including the electrically silent portion thereof-on X537A concentration, has been observed. An exponential dependence of "current" on "transmembrane potential" in the case of alamethicin is also confirmed. Possible errors in the technique are discussed.
Theoretical calculations of the permeability of monensin–cation complexes in model bio-membranes
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2000
Monensin is one of the best-characterized ionophores; it functions in the electroneutral exchange of cations between the extracellular and cytoplasmic sides of cell membranes. The X-ray crystal structures of monensin in free acid form and in complex with Na , K and Ag are known and we have recently measured the diffusion rates of monensin in free acid form (Mo^H) and in complex with Na (Mo^Na) and with K (Mo^K) using laser pulse techniques. The results have shown that Mo^H diffuses across the membrane one order of magnitude faster than Mo^Na and two orders of magnitude faster than Mo^K. Here, we report calculations of the translocation free energy of these complexes across the membrane along the most favorable path, i.e. the lowest free energy path. The calculations show that the most favorable orientation of monensin is with its hydrophobic furanyl and pyranyl moieties in the hydrocarbon region of the membrane and the carboxyl group and the cation at the water^membrane interface. Further, the calculations show that Mo^H is likely to be inserted deeper than MoN a into the bilayer, and that the free energy barrier for transfer of Mo^H across the membrane is V1 kcal/mol lower than for Mo^Na, in good agreement with our measurements. Our results show that the Mo^K complex is unlikely to diffuse across lipid bilayers in its X-ray crystal structure, in contrast to the Mo^H and Mo^Na complexes. Apparently, when diffusing across the membrane, the Mo^K complex assumes a different conformation and/or thinning defects in the bilayer lower significantly the free energy barrier for the process. The suitability of the model for treating the membrane association of small molecules is discussed in view of the successes and failures observed for the monensin system. ß
The mechanism of monensin-mediated cation exchange based on real time measurements
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1996
Monensin is an ionophore that supports an electroneutral inn exchange acro';s tile lipid bilayeL Because of Ihis. under steady-state conditions• no eleclric signals accompany its reactions. Using Ihe Laser Induced Proton fh.dsc as a synchronizing event we selectively acidify one face of a black lipid membrane impregnated by monensin. The short perturbation temporarily upsets the acid-base equilibrium on one face of the memblar.e, causing a transient cycle of ion exchange. Under such conditions the molecular events could bc discerned us a transienl electric polarization of the membrane lasting approx. 200 /~s. The proton-driven chemical reactions that lead to lhe electric signals had been reconstlucled by numeric integration of differential rate equations which constitute a maximalistic description of the multi equilibria nature of the system (Gutman. M. and Nachliel. E. (1989) Electrochim. Acta 34. Ig01-1g06}. The analysis of the reactions reveals that the ionic selectivity of the monendn (H ' > Na ÷ > K" ) is due to more than one term. Besides the well established different affinity tbr the various cations, the selectivity is also derived from a large difference in the rates of cross membranal diffusivities (Moll > MoNa > MoK). which have never been detueled belk~re. (v) Quantitative analysis of the membrane's crossing rates of the three nemral complexes reveals a major role of the membranal dipolar field in regulating ion transport. The diffusion of Moll, which has no dipole moment, is hindered only by the viscose drag. On the other hand, the dipolar complexes (MoNa and MoK) are delayed by dipole-dipole inlemctitm wilh the membrane. (vi) Comparison of the calculated dipoles with those estimated for the crystalline conformation of the [MoNa(H ~O)_~ ] and [MoK(H zO)z] complexes reveals that the MoNa may exist in the membrane at ils crystal e~mfiguratitm, while the MoK definitely attains a structure having a dipole moment larger than in the crystal.
Mitochondrial transport of cations: channels, exchangers, and permeability transition
1999
I. Introduction 1127 A. Mechanism of energy conservation and cation transport 1128 B. Membrane potential and equilibrium cation distribution 1129 II. Transport of Monovalent Cations 1129 A. Exchangers (antiports) 1130 B. Channels (uniports) 1132 C. Physiological role(s) of mitochondrial K ϩ cycle 1135 III. Transport of Calcium 1135 A. Nonequilibrium Ca 2ϩ distribution 1135 B. Pathways for Ca 2ϩ uptake 1136 C. Pathways for Ca 2ϩ efflux 1138 D. Mitochondria in Ca 2ϩ homeostasis 1140 IV. Permeability Transition 1141 A. Regulation 1141 B. Channel kinetics and population dynamics 1143 C. Consequences and reversibility 1143 D. Potential role in Ca 2ϩ release 1144 V. Appendix 1145 A. Ca 2ϩ-binding proteins 1145 B. Transport of Mg 2ϩ 1145 C. Electrophysiology 1146 D. Mitochondria and cell death 1146