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- Author or Editor: M. Mizuno x
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Abstract
The stability constants
, of monochloride complex of Eu(III) in the tracer concentrations have been determined in the mixed system of dimethyl sulfoxide
(DMSO) and water with 1.0 mol·dm−3 ionic strength using a solvent extraction technique. The values of
decrease up to about 0.2 mole fraction of DMSO (X
s
) in the mixed solvent system and then increase. Calculation of Eu3+−Cl− distance using a Born-type equation of the Gibbs' free energy derived from the
revealed that the estimated distance between Eu3+ and Cl− (d
Eu−Cl) increases linearly withX
s
in 0≤X
s
<0.043 and 0.043<X
s
<0.172, but their slopes are different. The line in the first region means a linear enlargement of the thickness of the primary
solvation sphere of Eu3+ with increasingX
s
. The larger slope againstX
s
in 0.043<X
s
<0.172 is attributable to lowering of
, based on the increase in the solvation number of the primary solvation sphere of Eu3+. The considerably large value ofd
Eu−Cl atX
s
=0.202 might result from lowering of
by a coordination of ClO
4
−
into the secondary solvation sphere of Eu3+ and the extremely drop ofd
Eu−Cl atX
s
=0.276 might reflect on a conversion of the ion-pair type, i.e., the coexistence of two kinds of a solvent-shared ion-pair
and a contact one by the appearance of the contact one.
Abstract
Purpose
Acid-base transport in renal proximal tubules (PTs) is mainly sodium-dependent and conducted in coordination by the apical Na+/H+ exchanger (NHE3), vacuolar H+-adenosine triphosphatase (V-ATPase), and the basolateral Na+/HCO3 - cotransporter. V-ATPase on PTs is well-known to play an important role in proton excretion. Recently we reported a stimulatory effect of insulin on these transporters. However, it is unclear whether insulin is involved in acid-base balance in PTs. Thus, we assessed the role of insulin in acid-base balance in PTs.
Methods
V-ATPase activity was evaluated using freshly isolated PTs obtained from mice, and specific inhibitors were then used to assess the signaling pathways involved in the observed effects.
Results
V-ATPase activity in PTs was markedly enhanced by insulin, and its activation was completely inhibited by bafilomycin (a V-ATPase-specific inhibitor), Akt inhibitor VIII, and PP242 (an mTORC1/2 inhibitor), but not by rapamycin (an mTORC1 inhibitor). V-ATPase activity was stimulated by 1 nm insulin by approximately 20% above baseline, which was completely suppressed by Akt1/2 inhibitor VIII. PP242 completely suppressed the insulin-mediated V-ATPase stimulation in mouse PTs, whereas rapamycin failed to influence the effect of insulin. Insulin-induced Akt phosphorylation in the mouse renal cortex was completely suppressed by Akt1/2 inhibitor VIII and PP242, but not by rapamycin.
Conclusion
Our results indicate that stimulation of V-ATPase activity by insulin in PTs is mediated via the Akt2/mTORC2 pathway. These results reveal the mechanism underlying the complex signaling in PT acid-base balance, providing treatment targets for renal disease.
