Intracellular diffusion in the presence of mobile buffers. Application to proton movement in muscle

Irving, Malcolm; Maylie, James; Sizto, Ning Leung; Chandler, W. K.

doi:10.1016/s0006-3495(90)82592-3

Cited by 60 publications

(69 citation statements)

References 12 publications

(21 reference statements)

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“…Several observations indicate that H ϩ diffusion in oocytes is restricted by the presence of immobile buffers (37)(38)(39). First, the decrease in pH in occurred with a delay after the onset of inward current (Fig.…”

Section: Fig 8 Effects Of Fccp On Oocytesmentioning

confidence: 94%

Permeation and Activation of the M2 Ion Channel of Influenza A Virus

Mould¹,

Drury²,

Frings³

et al. 2000

Journal of Biological Chemistry

148

166

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The M 2 ion channel protein of influenza A virus is essential for mediating protein-protein dissociation during the virus uncoating process that occurs when the virus is in the acidic environment of the lumen of the secondary endosome. The difficulty of determining the ion selectivity of this minimalistic ion channel is due in part to the fact that the channel activity is so great that it causes local acidification in the expressing cells and a consequent alteration of reversal voltage, V rev . We have confirmed the high proton selectivity of the channel (1.5-2.0 ؋ 10 6 ) in both oocytes and mammalian cells by using four methods as follows: 1) comparison of V rev with proton equilibrium potential; 2) measurement of pH in and V rev while Na The M 2 protein of influenza A virus is thought to function as an ion channel that permits protons to enter virus particles during virion uncoating in endosomes. In addition, in influenza virus-infected cells, the M 2 protein causes the equilibration of pH between the acidic lumen of the trans-Golgi network and the cytoplasm (reviewed in Refs. 1 and 2). The activity of the M 2 ion channel is inhibited by the antiviral drug amantadine (3-5). The mature M 2 protein consists of a 23-residue N-terminal extracellular domain, a single internal hydrophobic domain of 19 residues that acts as a transmembrane domain and forms the pore of the channel, and a 54-residue cytoplasmic tail (6). Chemical cross-linking studies showed the M 2 protein to exist minimally as a homotetramer (7-9). Statistical analysis of the ion channel activity of mixed oligomers also indicated that a homotetramer is the minimal active oligomeric form of the protein (10).Despite the small size of the active M 2 oligomer, several lines of evidence indicate that ion channel activity is intrinsic to the M 2 protein. First, ion channel activity has been observed in three different expression systems, Xenopus oocytes (3, 11, 12), mammalian cells (5, 13), and yeast (14). Second, M 2 channel activity has also been recorded in artificial lipid bilayers from a reconstituted peptide corresponding to the transmembrane domain of the M 2 protein (15) and from purified M 2 protein (16). Thus, due to its structural simplicity, the M 2 ion channel is a potentially useful model for the study of ion channels in general.Although a great deal of evidence indicates H ϩ is the biologically relevant ion for the role of M 2 protein in the life cycle of the influenza virus (1, 3, 17-22), other ions have been shown to be capable of flowing through the channel (12). In addition, the ion selectivity measured for the M 2 channel has been found to differ depending on whether the activity was measured in Xenopus oocytes or mammalian cells. When M 2 protein was expressed in oocytes, V rev was found to differ from the proton equilibrium potential, E Hϩ as [H ϩ ] out was varied (12). On the other hand, when M 2 protein was expressed in MEL cells, V rev was found to agree with E Hϩ (5). In a recent study (23), we found I Hϩ of the M 2 ion channel to...

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Section: Fig 8 Effects Of Fccp On Oocytesmentioning

confidence: 94%

Permeation and Activation of the M2 Ion Channel of Influenza A Virus

Mould¹,

Drury²,

Frings³

et al. 2000

Journal of Biological Chemistry

148

166

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“…The values of DEGTA and DC~GTA are both taken to be 1.7 • 10 -6 crn2/s (see first section of Results). The value of OH.app is taken to be 0.5 • 10 -6 cm2/s (Irving, Maylie, Sizto, and Chandler, 1990). With these parameters, the value of kc~ calculated from Eq.…”

Section: A[ca] Can Be Estimated With the Egta-phenol Red Methodsmentioning

confidence: 99%

Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA.

Pape

Jong

Chandler

1995

The Journal of General Physiology

129

295

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Sarcoplasmic reticulum (SR) Ca release was studied at 13-16~ in cut fibers (sarcomere length, 3.4-3.9 I~m) mounted in a double Vaseline-gap chamber. The amplitude and duration of the action-potential stimulated free [Ca] transient were reduced by equilibration with end-pool solutions that contained 20 mM EGTA with 1.76 mM Ca and 0.63 mM phenol red, a maneuver that appeared to markedly reduce the amount of Ca complexed by troponin. A theoretical analysis shows that, under these conditions, the increase in myoplasmic free [Ca] is expected to be restricted to within a few hundred nanometers of the SR Ca release sites and to have a time course that essentially matches that of release. Furthermore, almost all of the Ca that is released from the SR is expected to be rapidly bound by EGTA and exchanged for protons with a 1:2 stoichiometry. Consequently, the time course of SR Ca release can be estimated by scaling the ApH signal measured with phenol red by -13/2. The value of 13, the buffering power of myoplasm, was determined in fibers equilibrated with a combination of EGTA, phenol red, and fura-2; its mean value was 22 mM/pH unit. The Ca content of the SR (expressed as myoplasmic concentration) was estimated from the total amount of Ca released by either a train of action potentials or a depleting voltage step; its mean value was 2,685 I~M in the action-potential experiments and 2,544 IxM in the voltage-clamp experiments. An action potential released, on average, 0.14 of the SR Ca content with a peak rate of release of,'~5 %/ms. A second action potential, elicited 20 ms later, released only 0.6 times as much Ca (expressed as a fraction of the SR content), probably because Ca inactivation of Ca release was produced by the first action potential. During a depolarizing voltage step to 60 mV, the rate of Ca release rapidly increased to a peak value of~3 %/ms and then decreased to a quasi-steady level that was only 0.6 times as large; this decrease was also probably due to Ca inactivation of Ca release. SR Ca release was studied with small step depolarizations that open no more than one SR Ca channel in 7

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“…The diffusive H þ flux must match H þ production with H þ extrusion (and similarly, H þ depletion with H þ loading). However, because of the high intracellular buffering capacity, most H þ ions are bound to buffer molecules and can diffuse only as fast as the H þ buffer complex (Irving et al, 1990;Vaughan-Jones et al, 2002;Swietach et al, 2003). An indispensible role for smaller buffer molecules, such as amino acids, dipeptides, phosphates and carbon dioxide/bicarbonate (CO 2 /HCO 3 À ), is to shuttle H þ ions within cells (Figure 1a).…”

Section: Buffering Reactions and Membrane Transport Regulate Intracelmentioning

confidence: 99%

New insights into the physiological role of carbonic anhydrase IX in tumour pH regulation

et al. 2010

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In this review, we discuss the role of the tumour-associated carbonic anhydrase isoform IX (CAIX) in the context of pH regulation. We summarise recent experimental findings on the effect of CAIX on cell growth and survival, and present a diffusion-reaction model to help in the assessment of CAIX function under physiological conditions. CAIX emerges as an important facilitator of acid diffusion and acid transport, helping to overcome large cell-to-capillary distances that are characteristic of solid tumours. The source of substrate for CAIX catalysis is likely to be CO 2 , generated by adequately oxygenated mitochondria or from the titration of metabolic acids with HCO À 3 taken up from the extracellular milieu. The relative importance of these pathways will depend on oxygen and metabolite availability, the spatiotemporal patterns of the cell's exposure to hypoxia and on the regulation of metabolism by genes. This is now an important avenue for further investigation. The importance of CAIX in regulating tumour pH highlights the protein as a potential target for cancer therapy.

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Intracellular diffusion in the presence of mobile buffers. Application to proton movement in muscle

Cited by 60 publications

References 12 publications

Permeation and Activation of the M2 Ion Channel of Influenza A Virus

Permeation and Activation of the M2 Ion Channel of Influenza A Virus

Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA.

New insights into the physiological role of carbonic anhydrase IX in tumour pH regulation

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