Involvement of deoxygenation-induced increase in tyrosine kinase activity in sickle cell dehydration

Abstract

 Deoxygenation of sickle (SS) cells causes cationic alterations leading to cell dehydration by various mechanisms, including activation of Ca²⁺-sensitive K channels and possibly of K-Cl cotransport. Since an abnormal tyrosine kinase (TK) activity exists in SS cells we investigated the possible role of tyrosine phosphorylation in SS cell dehydration. In density-fractionated SS reticulocytes and discocytes, but not in normal red cells, deoxygenation increased membrane and cytosolic TK activities and tyrosine phosphorylation of band 3, independently of external Ca²⁺. These effects were abolished by the TK inhibitors methyl 2,5-dihydroxycinnamate (DiOH) or tyrphostin 47 (T47). Deoxygenation-induced Ca²⁺ uptake was not affected by the inhibitors and Na⁺ gain was reduced by T47 and not by DiOH. Both inhibitors decreased the loss of K⁺ and cellular dehydration. The effect of the inhibitors on K⁺ efflux was still observed in the absence of external Ca²⁺. These data indicate that the TK inhibitors do not interfere with deoxygenation-induced membrane permeabilization, but affect Ca²⁺-independent K⁺ efflux. It cannot be excluded, however, that the TK inhibitors also attenuate Ca²⁺-sensitive K⁺ efflux. Based on recent evidence from the literature, it is suggested that the diminution of K⁺ efflux results in part from inhibition of K-Cl cotransport activity.