INTRACELLULAR CALCIUM SIGNALS IN RESPONSE TO BRADYKININ IN INDIVIDUALNEUROBLASTOMA-CELLS

The Ca indicator fura 2 was used to study the modulation of cytoplasmi c Ca by bradykinin (Bk) in single N1E-115 murine neuroblastoma cells. Increases in cytoplasmic Ca in response to Bk were mediated by the B-2 receptor subtype. Responses to high concentrations of Bk (1-100 nM) w ere homogeneous and characterized by a rapidly rising transient that d ecayed to baseline in the continued presence of agonist, with a half t ime of 15 s. Responses to low concentrations of Bk (100-500 pM) were m ore heterogeneous, with longer latencies and often with oscillations. Pretreatment with thapsigargin for 20 min prevented the Ca response, s howing that the Ca change results from intracellular Ca release. Remov al of external Ca had little effect on the response to Bk, indicating that the agonist does not activate Ca influx. The extent of Ca release and refilling after Bk was tested with ionomycin. A saturating dose o f Bk (20 nM) mobilizes > 90% of stored Ca within 30 s, and this is rep laced slowly. Replacement of external Na by N-methyl-D-glucamine to bl ock Na/Ca exchange affected the Ca response, causing decreases in late ncy and in the period of Ca oscillations and increases in overall dura tion and peak amplitude of the response.