HEAD-ACTIVATOR INDUCED MITOSIS OF NH15-CA2 CELLS REQUIRES CALCIUM INFLUX AND HYPERPOLARIZATION

In NH15-CA2 cells head activator (HA) stimulates cell proliferation by acting in the GUM transition. Cells in mitosis were analyzed by flow cytometry 2-4 h after HA application. HA in a dose-dependent manner st imulated mitosis. Mitosis was prevented by preincubation of cells with pertussis toxin identifying the HA receptor as being G(i)-protein cou pled. As second effect of HA, an increase in intracellular calcium con centration was observed. This increase in calcium concentration was ab olished by inhibiting calcium influx from the extracellular space into NH15-CA2 cells either by chelating extracellular calcium with EGTA, o r by blocking calcium channels. The increase in intracellular calcium concentration led to an activation of calcium-dependent potassium chan nels. The higher potassium conductance resulted in hyperpolarization o f NH15-CA2 cells. Blocking calcium channels with nickel chloride or po tassium channels with tetraethylammonium chloride inhibited the effect of HA on cell proliferation. HA-induced mitosis was inhibited by char ybdotoxin and apamin, but not by a-dendrotoxin confirming the notion t hat Ca2+-dependent potassium channels are involved in mediating the ef fect of HA on cell division.