Transmembrane water influx via aquaporin-1 is inhibited by barbiturates and propofol in red blood cells

Abstract

Aquaporin-1 (AQP1) is known to be expressed at a high level in endothelial cell membranes and participates in water transfer into or across these cells. To evaluate possible effects of anesthetics on AQP1, a model assessing water permeability of erythrocytes was used, AQP1 being the exclusive water channel in red blood cells (RBC). RBC were suspended in hypertonic (1.35%) or hypotonic (0.45%) phosphate-buffered saline (PBS). Optical density was measured continuously in an aggregometer before and during subsequent addition of hypotonic (0.45%) or hypertonic (9%) PBS, respectively. Rates of change of optical density corresponded to the rate of volume change due to osmotic effects on net water flux across the RBC membrane. We compared actions of mercuric chloride (HgCl(2), definitive AQP1-blocker, 0.2 microM), and different anesthetic drugs, such as thiopental (50-200 microg/ml), phenobarbital (30-220 microg/ml), propofol (15-25 microg/ml), ketamine (3.5-11 microg/ml), midazolam (0.2-32.5 microg/ml), halothane (1.5 vol%), and isoflurane (2.3 vol%); the concentrations being in the one- to threefold range of clinically relevant plasma levels. Water transport into RBC (swelling) was inhibited by HgCl(2), thiopental, phenobarbital and propofol while ketamine, midazolam, halothane, and isoflurane had no effect. Efflux of water (shrinking) was also inhibited by HgCl(2), confirming a significant role of AQP1 in this model. In contrast, none of the tested anesthetic substances had any influence on water efflux. Comparison to chemically related drugs suggested oxidation of a strategic SH-group to be the mode of action. The anesthetics thiopental, phenobarbital, and propofol significantly inhibited influx of water into RBC, while water efflux remained unaffected in distinction to HgCl(2). These anesthetics thus acted as vectorial inhibitors, a hitherto undescribed phenomenon. Accordingly, some anesthetics may indeed affect transport of water via aquaporins.

Aquaporin-1 shifts the critical transmural pressure to compress the aortic intima and change transmural flow: theory and implications

“…Pressure-dependent intact aortic hydraulic conductivity, L P t , for blocked AQP1s. Submilimolar concentrations of HgCl 2 block trans-AQP1 channels in red blood cells (32). Nguyen et al (19) measured L P t at three ⌬P values, flushed with 5 M HgCl 2 to block EC AQP1s, remeasured L P t (⌬P), denuded, and measured L P mϩI (⌬P), all on the same vessel.…”

Mercury-sensitive water channels as possible sensors of water potentials in pollen

“…The most frequent use of Hg in physiology is to examine its effect on water transport where extensively applied to roots ( Wan et al , 2004 ; Ionenko et al , 2006 , 2010 , 2012 ; Zhou et al , 2007 ; Dustmamatov and Zholkevich, 2008 ; Ehlert et al , 2009 ; Devi et al , 2012 ) and other cells ( Henzler and Steudle, 2000 ), and in animal systems it has been used in numerous preparations, for example in Xenopus oocytes ( Barnes et al , 1999 ), epithelia ( Patil et al , 2001 ; Castillo et al , 2005 ; Philip et al , 2008 ), and diverse cell types ( Voigtlaender et al , 2002 ; Gao et al , 2005 ; Heo et al , 2008 ; Ismail et al , 2009 ; Campbell et al , 2012 ; Lee et al , 2012 ). In all these systems, other measurements on the cells involved are made subsequent to Hg binding for some time afterwards, involving different aspects of water movement: swelling, osmotic permeability, and hydraulic conductivities, among others.…”

Measurement of absolute cell volume, osmotic membrane water permeability, and refractive index of transmembrane water and solute flux by digital holographic microscopy

“…The high membrane water permeability of human RBCs is mainly determined by the endogenously expressed water channel AQP1. 35,36 In the past, approximately 4-fold higher values for the osmotic water permeability coefficient in human RBCs have been reported. 35 We cannot exclude that this discrepancy with our measurements might be due to a limited solution exchange in the cell chamber (≈1 s) that doesn't yield a sufficiently fast step response in extracellular osmolarity compared to the measured time constant τ, leading to an underestimation of the P f value for the RBC.…”