Sodium block and depolarization diminish P2Z-dependent Caentry in human B lymphocytes

Despite a high Ca²⁺-permeability of the P2Z receptor in human B lymphocytes, extracellular ATP⁴has only a minor effect on global [Ca²⁺]_i. The aim of this study was to reveal the mechanisms responsible for this discrepancy. We investigated the relationship between ATP⁴⁻-application, Ca_i²-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. ATP⁴-induced changes in whole-cell current and [Ca²]_iwere blocked by extracellular as well as intracellular Na⁺. Under current clamp conditions, ATP⁴⁻-induced Na⁺-entry diminished the Ca²⁺entry via reduction of the driving force. A substantial increase in [Ca²⁺]_iinduced by ATP⁴⁻was only observed in Na⁺-free solutions.The pathway of signal transduction activated by ATP⁴via 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.