Sodium block and depolarization diminish P2Z-dependent Ca2+ entry in humanB lymphocytes

Despite a high Ca2+-permeability of the P2Z receptor in human B lymphocytes , extracellular ATP(4-) has only a minor effect on global [Ca2+](i). The ai m of this study was to reveal the mechanisms responsible for this discrepan cy. We investigated the relationship between ATP(4-)-application, Ca-i(2+)- response, membrane current and membrane potential in two human B cell lines and in human tonsillar B cells. This Was achieved by a combination of FACS - and voltage clamp measurements and the usage of appropriate voltage- and Ca2+-sensitive fluorescent dyes. ATP(4-)-induced changes in whole-cell curr ent and [Ca2+](i) were blocked by extracellular as well as intracellular Na f. Under current clamp conditions, ATP(4-)-induced Nat-entry diminished the Ca2+ entry via reduction of the driving force. A substantial increase in [ Ca2+-](i) induced by ATP(4-) was only observed in Na+-free solutions. The pathway of signal transduction activated by ATP(4-) via P2Z receptor of human B lymphocytes under physiological conditions seems not to operate by an increase in the global intracellular Ca2+-concentration, but rather by the depolarization of the cell membrane as a result of the Na+-influx. (C) 2001 Harcourt Publishers Ltd.