Ca2+ Release from Inositol 1,4,5-Trisphosphate-Sensitive Ca2+ Store by Antidepressant Drugs in Cultured Neurons of Rat Frontal Cortex

Abstract: The ability of antidepressant drugs (ADs) to increase the concentration of intracellular Ca²⁺ (Ca²⁺]_i) was examined in primary cultured neurons from rat frontal cortices using the Ca²⁺-sensitive fluorescent indicator fura-2. Amitriptyline, imipramine, desipramine, and mianserin elicited transient increases in Ca²⁺]_i in a concentration-dependent manner (100 μM to 1 mM). These four AD-induced Ca²⁺]_i increases were not altered by the absence of external Ca²⁺ or by the presence of La³⁺ (30 μM), suggesting that these ADs provoked intracellular Ca²⁺ mobilization rather than Ca²⁺ influx. All four ADs increased inositol 1,4,5-trisphosphate (IP₃) contents by 20–60% in the cultured cells. The potency of the IP₃ production by these ADs closely correlated with the AD-induced Ca²⁺]_i responses. Pretreatment with neomycin, an inhibitor of IP₃ generation, significantly inhibited amitriptyline- and imipramine-induced Ca²⁺]_i increases. In addition, by initially perfusing with bradykinin (10 μM) or acetylcholine (10 μM), which can stimulate the IP₃ generation and mobilize the intracellular Ca²⁺, the amitriptyline responses were decreased by 76% and 69%, respectively. The amitriptyline-induced Ca²⁺]_i increases were unaffected by treatment with pertussis toxin. We conclude that high concentrations of amitriptyline and three other ADs mobilize Ca²⁺ from IP₃-sensitive Ca²⁺ stores and that the responses are pertussis toxin-insensitive. However, it seems unlikely that the effects requiring high concentrations of ADs are related to the therapeutic action.