Effects of Divalent Cations, Trypsin, and Phospholipases on the Passive Permeability to Sodium of Inside-Out Vesicles From Human Red Cells
✍ Scribed by Robert A. Colvin; James W. Green
- Publisher
- John Wiley and Sons
- Year
- 1982
- Tongue
- English
- Weight
- 784 KB
- Volume
- 18
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
Abstract
Inside‐out vesicles (IOV) were prepared from human red blood cells. Steady‐state uptake of ^22^Na was observed to generally follow an exponential time course with a rate constant of 1.57 ± 0.09 h^−1^ (SE). One week of cold storage (0–4°C) increased the rate constant to 2.50 ± 0.12 h ^−1^ (SE). Mg^2+^, Ca^2+^, or Sr^2+^ decreased the rate of ^22^Na uptake with no observable differences between the three divalent cations when tested at concentrations of 50 __μ__M. Mg^2+^ was shown to decrease the rate of ^22^Na uptake at concentrations as low as 5 __μ__M with maximal effect at 50 to 100 __μ__M. The decrease in rate of ^22^Na uptake induced by Mg^2+^ could be enhanced by exposure of IOV to Mg^2+^ for longer periods of time. Trypsin treatment of IOV increased the rate of uptake of ^22^Na and was dependent on the concentration of trypsin added between 5 to 25 __μ__g/ml (treated for 5 min at 25°C). The ability of Mg^2+^ (50 __μ__M) to decrease the rate of ^22^Na uptake was still observed after maximal trypsin treatment. Phospholipase A~2~ or phospholipase C treatment of IOV increased the rate of ^22^Na uptake and was dependent on the amount of phospholipase A~2~ (0.1 to 1.0 units/ml) or phospholipase C (0.25 to 2.5 units/ml) added (treated for 5 min at 25°C). After phospholipase A~2~ treatment, the observed decrease in the rate of ^22^Na uptake induced by Mg^2+^ (50 __μ__M) was generally greater than controls. After phospholipase C treatment, the observed decrease in rate of ^22^Na uptake induced by Mg^2+^ (50 __μ__M) was less or absent when compared with controls. Phospholipase C treatment was less effective in preventing the Mg^2+^ effect the longer IOV were exposed to Mg^2+^. The results suggest that Mg^2+^ binds to phospholipid head‐groups to reduce Na permeability perhaps by inducing a change in bilayer structure or phospholipid association.