Thiopental Elevates Steady-State Levels of Intracellular Ca2+ and Zn2+ in Rat Thymic Lymphocytes

Abstract

Thiopental is an ultra-short-acting barbiturate and has been used commonly in the induction phase of general anesthesia. However, the toxic effect of thiopental is not completely clear. The effect of thiopental on intracellular Ca2+ ([Ca2+]i) levels was investigated in non-excitable cells. Experiments were carried out using a flow-cytometric technique, rat thymic lymphocytes (as non-excitable cells), and appropriate fluorescent probes. Treatment of cells with 300 µM thiopental increased Fluo-3 fluorescence intensity, indicating elevation of [Ca2+]i. This increase was partially attenuated by a chelator of intracellular Zn2+. Thus, thiopental elevated both [Ca2+]i and intracellular Zn2+ ([Zn2+]i) levels. Under intracellular Zn2+-free conditions, 100–300 µM thiopental was still able to induce a statistically significant increase in [Ca2+]i, whereas removal of extracellular Ca2+ greatly reduced the increase in [Ca2+]i induced by this dose of thiopental. Therefore, the thiopental-induced increase in [Ca2+]i was mainly due to an increased influx of Ca2+. Treatment of cells with 300 µM thiopental increased FluoZin-3 fluorescence intensity, indicating the presence of [Zn2+]i, both in the presence and absence of extracellular Zn2+. The thiopental-induced elevation of [Zn2+]i was due to an increase in both influx of Zn2+ and intracellular Zn2+ release. Concanavalin A (10 µg/mL) augmented Fluo-3 fluorescence in the presence of an intracellular Zn2+ chelator. The combination of concanavalin A and 100–300 µM thiopental synergistically increased [Ca2+]i. Results suggest that thiopental increases [Ca2+]i in both quiescent and activated lymphocytes, possibly resulting in modulation of immune system function.