Abstract
In contrast to rat and human erythrocytes, nucleated erythrocytes from two fish species ( Cyprinus carpio and Salmo trutta) underwent almost complete haemolysis in 20 min of EDTA addition. Using Ca 2+/Mg 2+ EGTA-citrate buffer, we observed that half-maximal haemolysis of fish erythrocytes occurs at [Ca 2+] o ∼10 μM independently of extracellular Mg 2+ concentration. Attenuation of [Ca 2+] o with EGTA also decreased stability of the plasma membrane of vascular smooth muscle cells (VSMC) and HeLa cells, indicated by a three- to five-fold elevation of lactate dehydrogenase release and passive permeability of plasma membrane for Na +. In VSMC, EGTA lowered [Ca 2+] i by ∼20%. This effect was absent in VSMC-loaded with the intracellular Ca 2+ chelator BAPTA. In contrast to EGTA, BAPTA did not affect haemoglobin release from fish erythrocytes and passive permeability for Na + in VSMC. Viewed collectively, our data show that in nucleated cells, extracellular Ca 2+ plays a crucial role in the maintenance of plasma membrane integrity.
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