The Tension-sensitive Ion Transport Activity of MSL8 is Critical for its Function in Pollen Hydration and Germination

Block copolymers composed of polyoxyethylene and polyoxypropylene were found to increase the influx of Na+ and the efflux of K+ from human erythrocytes. They were, however, ineffective at promoting the transport of Ca2+. The size of the ion fluxes induced by the copolymers correlated with their efficacy in stimulating inflammation. These compounds were also found to induce conductance increases in planar lipid bilayers in a nonvoltage dependent and nonstepwise manner. In both experimental systems, ion transport was facilitated only under temperature and ionic-strength conditions in which the polymers form aggregates in aqueous solution. In neither system did the concentration dependence of transport activity exhibit a pronounced cooperativity. These observations are consistent with the view that aqueous monomers of these surface active agents partition into the membrane, where they facilitate the conductive movement of monovalent cations by means of a carrier type mechanism. As a novel class of ionophores, these substances are of practical interest because they can be water soluble and are potentially reversible.

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Altered pHi regulation and Na+/HCO3− transporter activity in choroid plexus of cilia-defective Tg737orpk mutant mouse

AJP Cell Physiology ◽

10.1152/ajpcell.00408.2006 ◽

2007 ◽

Vol 292 (4) ◽

pp. C1409-C1416 ◽

Cited By ~ 43

Author(s):

Boglarka Banizs ◽

Peter Komlosi ◽

Mark O. Bevensee ◽

Erik M. Schwiebert ◽

Phillip D. Bell ◽

...

Keyword(s):

Ion Transport ◽

Choroid Plexus ◽

Perinatal Period ◽

Ependymal Cells ◽

Intracellular Camp ◽

Transport Activity ◽

Wild Type ◽

Choroid Plexus Epithelium ◽

Fluid Movement ◽

Camp Levels

Tg737 orpk mice have defects in cilia assembly and develop hydrocephalus in the perinatal period of life. Hydrocephalus is progressive and is thought to be initiated by abnormal ion and water transport across the choroid plexus epithelium. The pathology is further aggravated by the slow and disorganized beating of motile cilia on ependymal cells that contribute to decreased cerebrospinal fluid movement through the ventricles. Previously, we demonstrated that the hydrocephalus phenotype is associated with a marked increase in intracellular cAMP levels in choroid plexus epithelium, which is known to have regulatory effects on ion and fluid movement in many secretory epithelia. To evaluate whether the hydrocephalus in Tg737 orpk mutants is associated with defects in ion transport, we compared the steady-state pHi and Na+-dependent transport activities of isolated choroid plexus epithelium tissue from Tg737 orpk mutant and wild-type mice. The data indicate that Tg737 orpk mutant choroid plexus epithelium have lower pHi and higher Na+-dependent HCO3− transport activity compared with wild-type choroid plexus epithelium. In addition, wild-type choroid plexus epithelium could be converted to a mutant phenotype with regard to the activity of Na+-dependent HCO3− transport by addition of dibutyryl-cAMP and mutant choroid plexus epithelium toward the wild-type phenotype by inhibiting PKA activity with H-89. Together, these data suggest that cilia have an important role in regulating normal physiology of choroid plexus epithelium and that ciliary dysfunction in Tg737 orpk mutants disrupts a signaling pathway leading to elevated intracellular cAMP levels and aberrant regulation of pHi and ion transport activity.

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Modulation of the Na,K-pump function by beta subunit isoforms.

The Journal of General Physiology ◽

10.1085/jgp.103.4.605 ◽

1994 ◽

Vol 103 (4) ◽

pp. 605-623 ◽

Cited By ~ 106

Author(s):

F Jaisser ◽

P Jaunin ◽

K Geering ◽

B C Rossier ◽

J D Horisberger

Keyword(s):

Ion Transport ◽

Pump Current ◽

Beta Subunit ◽

Beta Subunits ◽

Transport Activity ◽

Apparent Affinity ◽

Significant Difference ◽

Ouabain Sensitivity ◽

External K

To study the role of the Na,K-ATPase beta subunit in the ion transport activity, we have coexpressed the Bufo alpha 1 subunit (alpha 1) with three different isotypes of beta subunits, the Bufo Na,K-ATPase beta 1 (beta 1NaK) or beta 3 (beta 3NaK) subunit or the beta subunit of the rabbit gastric H,K-ATPase (beta HK), by cRNA injection in Xenopus oocyte. We studied the K+ activation kinetics by measuring the Na,K-pump current induced by external K+ under voltage clamp conditions. The endogenous oocyte Na,K-ATPase was selectively inhibited, taking advantage of the large difference in ouabain sensitivity between Xenopus and Bufo Na,K pumps. The K+ half-activation constant (K1/2) was higher in the alpha 1 beta 3NaK than in the alpha 1 beta 1NaK groups in the presence of external Na+, but there was no significant difference in the absence of external Na+. Association of alpha 1 and beta HK subunits produced active Na,K pumps with a much lower apparent affinity for K+ both in the presence and in the absence of external Na+. The voltage dependence of the K1/2 for external K+ was similar with the three beta subunits. Our results indicate that the beta subunit has a significant influence on the ion transport activity of the Na,K pump. The small structural differences between the beta 1NaK and beta 3NaK subunits results in a difference of the apparent affinity for K+ that is measurable only in the presence of external Na+, and thus appears not to be directly related to the K+ binding site. In contrast, association of an alpha 1 subunit with a beta HK subunit results in a Na,K pump in which the K+ binding or translocating mechanisms are altered since the apparent affinity for external K+ is affected even in the absence of external Na+.

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SOS2 Promotes Salt Tolerance in Part by Interacting with the Vacuolar H+-ATPase and Upregulating Its Transport Activity

Molecular and Cellular Biology ◽

10.1128/mcb.00430-07 ◽

2007 ◽

Vol 27 (22) ◽

pp. 7781-7790 ◽

Cited By ~ 142

Author(s):

Giorgia Batelli ◽

Paul E. Verslues ◽

Fernanda Agius ◽

Quansheng Qiu ◽

Hiroaki Fujii ◽

...

Keyword(s):

Salt Stress ◽

Salt Tolerance ◽

Atpase Activity ◽

Ion Transport ◽

Affinity Purification ◽

Tandem Affinity Purification ◽

Mass Spectrometry Analysis ◽

Transport Activity ◽

Sos Pathway

ABSTRACT The salt overly sensitive (SOS) pathway is critical for plant salt stress tolerance and has a key role in regulating ion transport under salt stress. To further investigate salt tolerance factors regulated by the SOS pathway, we expressed an N-terminal fusion of the improved tandem affinity purification tag to SOS2 (NTAP-SOS2) in sos2-2 mutant plants. Expression of NTAP-SOS2 rescued the salt tolerance defect of sos2-2 plants, indicating that the fusion protein was functional in vivo. Tandem affinity purification of NTAP-SOS2-containing protein complexes and subsequent liquid chromatography-tandem mass spectrometry analysis indicated that subunits A, B, C, E, and G of the peripheral cytoplasmic domain of the vacuolar H+-ATPase (V-ATPase) were present in a SOS2-containing protein complex. Parallel purification of samples from control and salt-stressed NTAP-SOS2/sos2-2 plants demonstrated that each of these V-ATPase subunits was more abundant in NTAP-SOS2 complexes isolated from salt-stressed plants, suggesting that the interaction may be enhanced by salt stress. Yeast two-hybrid analysis showed that SOS2 interacted directly with V-ATPase regulatory subunits B1 and B2. The importance of the SOS2 interaction with the V-ATPase was shown at the cellular level by reduced H+ transport activity of tonoplast vesicles isolated from sos2-2 cells relative to vesicles from wild-type cells. In addition, seedlings of the det3 mutant, which has reduced V-ATPase activity, were found to be severely salt sensitive. Our results suggest that regulation of V-ATPase activity is an additional key function of SOS2 in coordinating changes in ion transport during salt stress and in promoting salt tolerance.

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