EXOGENOUS HEAT-SHOCK PROTEIN HSP70 ACTIVATES POTASSIUM CHANNELS IN U937 CELLS

With the use of patch clamp technique. the effect of exogenous heat sh ock protein hsp70 on ion channel properties in the plasma membrane of human promonocyte U937 cells has been examined. Cell-attached experime nts showed that the addition of 30-100 mu g/ml hsp70 to the pipette so lution resulted in an activation of outward currents through potassium -selective channels of 9 pS unitary conductance. The activity of K+-se lective channels did not depend on membrane voltage and could be contr olled by the intracellular free calcium concentration as revealed in i nside-out recordings. K+ channels with similar conductance and kinetic behaviour were found in normal cell-attached patches very rarely. Out side-out experiments showed that the addition of hsp70 to the external solution induced a channel-like stepwise increase of inward current w hich may provide cation entry from the extracellular medium. The inter action of extracellular hsp70 with the membrane surface of the native cell and of the excised fragment was found to be different. The result s suggest that hsp70-induced activation of Ca-dependent K channels in monocyte-macrophage cells may be due to a local increase of foe Ca2+ c oncentration just near the inner membrane side.