Proton flux in large unilamellar vesicles in response to membrane potentials and pH gradients

Redelmeier, Thomas E.; Mayer, Lawrence D.; Wong, Kenneth; Bally, Marcel B.; Cullis, Pieter R.

doi:10.1016/s0006-3495(89)82684-0

Cited by 40 publications

(9 citation statements)

References 30 publications

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“…After the initial phase, an exponential decay phase then follows, where the pH i of the cells decreases towards pH ex (figure 4). The relatively good single exponential fit suggests that only passive diffusion controls the change in pH i after the start of the exponential decay [23,33]. As thermal deactivation of transporters and pumps in the cell membrane occurs, the cell will lose the ability to actively regulate the pH i .…”

Section: Discussionmentioning

confidence: 99%

Intracellular pH distribution as a cell health indicator in Saccharomyces cerevisiae

Aabo

Glückstad

Siegumfeldt

et al. 2011

J. R. Soc. Interface.

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Internal pH regulation is vital for many cell functions, including transport mechanisms and metabolic enzyme activity. More specifically, transport mechanisms are to a wide degree governed by internal pH distributions. We introduce the term standard deviation of the intracellular pH (s.d.( pH int )) to describe the internal pH distributions. The cellular pH distributional response to external stress such as heat has not previously been determined. In this study, the intracellular pH ( pH i ) and the s.d.( pH int ) of Saccharomyces cerevisiae cells exposed to supralethal temperatures were measured using fluorescence ratio imaging microscopy (FRIM). An exponential decline in pH i was observed after an initial small decline. For the first time, we report the use of FRIM for determining in vivo plasma membrane proton permeability coefficients in yeast. Furthermore, the exponential decay of pH i and the rupture of the cell plasma membrane, as measured by propidium iodide staining, at 708C were not simultaneous but were separated by a significant temporal difference. Finally, a nonlinear relationship between the pH i and s.d.( pH int ) was found; i.e. the s.d.( pH int ) was significantly more sensitive to supralethal temperatures than pH i . s.d.( pH int ) is therefore proposed as an early health/vitality indicator in S. cerevisiae cells exposed to heat stress.

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Section: Discussionmentioning

confidence: 99%

Intracellular pH distribution as a cell health indicator in Saccharomyces cerevisiae

Aabo

Glückstad

Siegumfeldt

et al. 2011

J. R. Soc. Interface.

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“…pH-partition hypothesis). However, recent studies suggest H + /OH permeability to be surprisingly high, as high as 10 -4 cm/s, greatly exceeding that of about 10 -12 cm/s for Na + [373][374][375][376][377][378][379][380][381]. Biegel and Gould [381] rapidly changed the pH ("acid pulse measurements") of a suspension of SUV (small unilamellar vesicles, soybean PC) from the equilibrated pH 8.2 to the external pH 6.65, and monitored the rate of influx of H + into the vesicles.…”

Section: Water Wires and H + /Oh -Currentsmentioning

confidence: 99%

Physicochemical Profiling (Solubility, Permeability and Charge State)

Avdeef¹

2004

Frontiers in Medicinal Chemistry - Online

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About 30% of drug candidate molecules are rejected due to pharmacokineticrelated failures. When poor pharmaceutical properties are discovered in development, the costs of bringing a potent but poorly absorbable molecule to a product stage by "formulation" can become very high. Fast and reliable in vitro prediction strategies are needed to filter out problematic molecules at the earliest stages of discovery. This review will consider recent developments in physicochemical profiling used to identify candidate molecules with physical properties related to good oral absorption. Poor solubility and poor permeability account for many PK failures. FDA's Biopharmaceutics Classification System (BCS) is an attempt to rationalize the critical components related to oral absorption. The core idea in the BCS is an in vitro transport model, centrally embracing permeability and solubility, with qualifications related to pH and dissolution. The objective of the BCS is to predict in vivo performance of drug products from in vitro measurements of permeability and solubility. In principle, the framework of the BCS could serve the interests of the earliest stages of discovery research. The BCS can be rationalized by considering Fick's first law, applied to membranes. When molecules are introduced on one side of a lipid membrane barrier (e.g., epithelial cell wall) and no such molecules are on the other side, passive diffusion will drive the molecules across the membrane. When certain simplifying assumptions are made, the flux equation in Fick's law reduces simply to a product of permeability and solubility. Many other measurable properties are closely related to permeability and solubility. Permeability (P e) is a kinetic parameter related to lipophilicity (as indicated by the partition and distribution coefficients, log P and log D). Retention (R) of lipophilic molecules by the membrane (which is related to lipophilicity and may predict PK volumes of distribution) influences the characterization of permeability. Furthermore, strong drug interactions with serum proteins can influence permeability. The unstirred water layer on both sides of the membrane barrier can impose limits on permeability. Solubility (S) is a thermodynamic parameter, and is closely related to dissolution, a kinetic parameter. The unstirred water layer on the surfaces of suspended solids imposes limits on dissolution. Bile acids effect both solubility and dissolution, by a micellization effect. For ionizable molecules, pH plays a crucial role. The charge state that a molecule exhibits at a particular pH is characterized by the ionization constant (pK a) of the molecule. Buffers effect pH gradients in the unstirred water layers, which can dramatically affect both permeability and dissolution of ionizable molecules. In this review, we will focus on the emerging instrumental methods for the measurement of the physicochemical parameters P e, S, pKa, R, log P, and log D (and their pH-profiles). These physicochemical profiles can be valuable tools for the medicinal che...

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“…Membrane potentials (negative inside) and transmembrane pH gradients (acidic inside) were assessed by measuring the transbilayer distribution of [3H]TPP+ and ['4C]MeAm employing the minicolumn separation method described above (Rottenberg, 1979;Hope et al, 1985;Redelmeier et al, 1989). [3H]TPP+ was added at 1 ,uCi/ml (corresponds to 0.026 nM) and ['4C]MeAm at 0.24 ,uCi/ml (5.8 ,uM) final concentrations to the vesicle suspensions in the presence or absence of peptide.…”

Section: Determination Of A*4 and Aphmentioning

confidence: 99%

“…The methylamine distribution was translated to a ApH value according to ApH = log ([MeAm]jj/[MeAm]O). Redelmeier et al (1989) have demonstrated that the MeAm distribution provides an accurate measure of the pH gradient between the interior and exterior aqueous compartments.…”

Section: Determination Of A*4 and Aphmentioning

confidence: 99%

“…To elucidate the mechanism by which the peptide attains a localization in the interface of the inner bilayer leaflet, the involvement of the pH gradient and the influence of the pH have been investigated. It is well established that due to the proton permeability of the lipid bilayer, a K+ diffusion potential evokes a transbilayer pH gradient (Nichols et al, 1980;Cafiso and Hubbell, 1983;Redelmeier et al, 1989).…”

Section: The Roles Of Aw Aph and Phmentioning

confidence: 99%

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Ion gradient-induced membrane translocation of model peptides

Kroon¹,

Vogt²,

Hof³

et al. 1991

Biophysical Journal

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The K+ diffusion potential-induced association of synthetic model peptides carrying a single positive charge originating from the NH2-terminal amino function with large unilamellar vesicles (LUV) consisting of phosphatidylcholine (PC) has been reported previously (de Kroon, A. I. P. M., J. de Gier, and B. de Kruijff. 1989. Biochim. Biophys. Acta. 981:371-373). To determine the vesicle localization of the associated peptides, fluorescence measurements utilizing the peptides' tryptophan residue as intrinsic fluorescent probe were performed. The application in these measurements, of vesicles that exhibit an asymmetric transbilayer distribution of brominated PC which is a quencher of tryptophan fluorescence, unequivocally demonstrated that the peptide H3N(+)-AIMLWA-Ome (AIXme+) is accumulated in the interface of the inner leaflet of the vesicle membrane in response to the valinomycin-induced K+ diffusion potential (negative inside). The relative contributions of the membrane potential (delta psi) and the pH gradient (delta pH, acidic inside) induced by the K+ diffusion potential, to the process have been assessed. An analysis of the pH and delta pH dependencies of the process demonstrated that the K+ diffusion potential-induced peptide accumulation is largely determined by a redistribution of peptide according to the transbilayer pH gradient, in agreement with a translocation across the vesicle membrane of the neutral, deprotonated form of the peptide. The general validity of the mechanism proposed for the vesicle-uptake of AIXme+ has been examined by extending the experiments to peptide analogues with a single negative charge and to peptides with two positive charges, and by investigating the effect of incorporating the acidic phospholipid cardiolipin (CL) into the LUV. The incorporation of CL appeared not to affect the K+ diffusion, potential-induced vesicle uptake of AIXme+. The peptide H3N(+)-RMLWA-Ome (RXme2+) showed a small delta pH independent fluorescence response to the delta psi upon raising the CL content of the vesicles to 25%.

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Proton flux in large unilamellar vesicles in response to membrane potentials and pH gradients

Cited by 40 publications

References 30 publications

Intracellular pH distribution as a cell health indicator in Saccharomyces cerevisiae

Intracellular pH distribution as a cell health indicator in Saccharomyces cerevisiae

Physicochemical Profiling (Solubility, Permeability and Charge State)

Ion gradient-induced membrane translocation of model peptides

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