Mitogen-induced oscillations of cytosolic Ca2l and transmembrane Ca2+ current in human leukemic T cells

A rapid rise in the level of cytosolic free calcium ([Ca2+],) is believed to be one of several early trig-gering signals in the activation of T lymphocytes by antigen. Although Ca2 " release from intracellular stores and its contribution to Ca2+ signaling in many cell types is well documented, relatively little is known regarding the role and mechanism of Ca2 ' entry across the plasma membrane. We have investigated mitogen-triggered Ca2+ signaling in individual cells of the human T-leukemia-derived line, Jurkat, using fura-2 imaging and patch-clamp recording techniques. Phytohemagglutinin (PHA), a mitogenic lectin, in-duces repetitive [Ca2]i oscillations in these cells peaking at micromolar levels with a period of 90-120 s. The oscillations depend critically upon Ca2+ influx across the plasma membrane, as they are rapidly terminated by removal of extracellular Ca2+, addition of Ca2"-channel blockers such as Ni2+ or Cd2+, or membrane depolarization. Whole-cell and perforated-patch recording methods were combined with fura-2 measurements to identify the mitogen-activated Ca2+ conductance involved in this response. A small, highly selective Ca2+ conductance becomes activated spontaneously in whole-cell recordings and in re-sponse to PHA in perforated-patch experiments. This conductance has properties consistent with a role in T-cell activation, including activation by PHA, lack of voltage-dependent gating, inhibition by Ni2+ or Cd2+, and regulation by intracellular Ca2. Moreover, a tight temporal correlation between oscillations of Ca2+ conductance and [Ca2+]i suggests a role for the membrane Ca2+ conductance in generating [Ca2+] oscillations in activated T cells