Nigericin-mediated H+, K+ and Na+ transports across vesicular membrane: T-jump studies

Prabhananda, B. S.; Ugrankar, Madhuri M.

doi:10.1016/0005-2736(91)90090-u

Cited by 23 publications

(32 citation statements)

References 22 publications

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“…The SBPL vesicle solutions with 2 mM pyranine inside and other concentration conditions as given in the figure legends were prepared from asolectin (Sigma, St. Louis, MO), following the procedure described elsewhere (Krishnamoorthy, 1986;Prabhananda and Ugrankar, 1991). In our experiments MCl (M ϩ ϭ Li ϩ , Na ϩ , K ϩ , and Cs ϩ ) were used to regulate concentrations of M ϩ in the SBPL vesicle solutions.…”

Section: Methodsmentioning

confidence: 99%

“…Stock solutions of 5 mM CAL (Sigma) in ethanol were added in microliter amounts to vesicle solutions with vortex stirring. T-jump was used to create ⌬pH (ϳ0.02) and the ⌬pH decay was observed at 23 Ϯ 1.5°C by monitoring the fluorescence from the pH indicator pyranine entrapped inside vesicles (Prabhananda and Ugrankar, 1991). The observed ⌬pH decay traces were single exponentials.…”

Section: Methodsmentioning

confidence: 99%

“…The observed ⌬pH decay traces were single exponentials. The ⌬pH relaxation times were measured by comparing the observed trace with those obtained from a calibrated exponential generator (Prabhananda and Ugrankar, 1991).…”

Section: Methodsmentioning

confidence: 99%

“…When the H ϩ transport step is sufficiently fast and the ⌬pH decay rate is limited by the M ϩ transport step, the CAL-species transporting M ϩ across the membrane can be identified by the above procedure. In our experiments, soybean phospholipid (SBPL) vesicles were used as model membranes for reasons mentioned elsewhere, and temperature jump (T-jump) was used to create ⌬pH across the vesicular membrane (Krishnamoorthy, 1986;Prabhananda and Ugrankar, 1991).…”

Section: Introductionmentioning

confidence: 99%

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Evidence for Dimer Participation and Evidence Against Channel Mechanism in A23187-Mediated Monovalent Metal Ion Transport Across Phospholipid Vesicular Membrane

Prabhananda

Kombrabail

1998

Biophysical Journal

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The decay of the pH difference (DeltapH) across soybean phospholipid vesicular membrane by ionophore A23187 (CAL)-mediated H+/M+ exchange (M+ = Li+, Na+, K+, and Cs+) has been studied in the pH range 6-7.6. The DeltapH in these experiments were created by temperature jump. The observed dependence of DeltapH relaxation rate 1/tau on the concentration of CAL, pH, and the choice of M+ in vesicle solutions lead to the following conclusions. 1) The concentrations of dimers and other oligomers of A23187 in the membrane are small compared to the total concentration of A23187 in the membrane, similar to that in chloroform solutions reported in the literature. 2) In the H+ transport cycle leading to DeltapH decay, the A23187-mediated H+ translocation across the membrane is a fast step, and the rate-limiting step is the A23187-mediated M+ translocation. 3) Even though the monomeric Cal-H is the dominant species translocating H+, Cal-M is not the dominant species translocating M+ (even at concentrations higher than [Cal-H]), presumably because its dissociation rate is much higher than its translocation rate. 4) The pH dependence of 1/tau shows that the dimeric species Cal2LiLi, Cal2NaNa, Cal2KH, and Cal2CsH are the dominant species translocating M+. The rate constant associated with their translocation has been estimated to be approximately 5 x 10(3) s-1. With this magnitude for the rate constants, the dimer dissociation constants of these species in the membrane have been estimated to be approximately 4, 1, 0.05, and 0.04 M, respectively. 5) Contrary to the claims made in the literature, the data obtained in the DeltapH decay studies do not favor the channel mechanism for the ion transport in this system. 6) However, they support the hypothesis that the dissociation of the divalent metal ion-A23187 complex is the rate limiting step of A23187-mediated divalent metal ion transport.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evidence for Dimer Participation and Evidence Against Channel Mechanism in A23187-Mediated Monovalent Metal Ion Transport Across Phospholipid Vesicular Membrane

Prabhananda

Kombrabail

1998

Biophysical Journal

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“…Based on their results, we selected P3CA-15C5 for more detailed studies using a well-defined phospholipid vesicle system that provides a more realistic model of biological membranes [21,22]. Our group and others have used this type of system to study the selectivity and mechanisms of cation transport mediated by other ionophores [12][13][14][21][22][23][24][25][26][27]. In this paper, we report the results of transport studies which show that P3CA-15C5 is an effective and selective ionophore for Cd 2+ and Pb 2+ , and that the predominant transport mechanisms in phospholipid bilayer membranes are electrogenic.…”

Section: Introductionmentioning

confidence: 99%