Selective serotonin reuptake inhibitors (SSRIs) suppress Na+- dependent Mg2+ efflux in rat ventricular myocytes

Abstract

Na⁺/Mg²⁺ exchange transport, the Na⁺ gradient-driven Mg²⁺ extrusion system, plays a key role in cellular Mg²⁺ homeostasis. To date, the molecular entity and selective inhibitors of Na⁺/Mg²⁺ exchanger have not been fully explored. Intracellular free Mg²⁺ concentration ([Mg²⁺]_i) was measured in ventricular myocytes acutely isolated from rat hearts. After soaking the cells in high-Mg²⁺ low-Na⁺ solution to increase [Mg²⁺]_i, the addition of extracellular Na⁺ caused a decrease in [Mg²⁺]_i. We analyzed the rate of decrease in [Mg²⁺]_i as Na⁺/Mg²⁺ exchange transport activity. The suppression of the rate of decrease in [Mg²⁺]_i caused by sertraline, a selective serotonin reuptake inhibitor (SSRI), was concentration dependent (IC₅₀ 8.9 μM) and reversible. Other SSRIs, namely paroxetine and fluvoxamine, were less effective than sertraline. In conclusion, sertraline inhibited Na⁺/Mg²⁺ exchange transport more effectively than any previously reported inhibitors of Na⁺/Mg²⁺ exchanger. Sertraline could be used as a tool to characterize the functions of Na⁺/Mg²⁺ exchanger.

Keywords: Cardiomyocytes; Fluvoxamine; Magnesium; Na(+)-dependent Mg(2+) efflux; Na(+)/Mg(2+) exchange; Paroxetine; Selective serotonin reuptake inhibitor (SSRI); Sertraline.

Fig. 1

Selective serotonin reuptake inhibitors (SSRIs) did not change the Mg²⁺-related signal in vitro. The fluorescence signals [F(382)/F(350)] were measured from solutions including 50 μM furaptra with 50 μM sertraline (□), 50 μM fluvoxamine (○), 50 μM paroxetine (△), or without SSRI (×). Each symbol (mean ± SD, n = 3) was plotted as a function of [Mg²⁺] (mM) of solutions.

Fig. 2

Representative records from separate experiments on the effects of sertraline. Mg²⁺-loaded cells were perfused with Ca²⁺-free Tyrode’s solution in the absence of sertraline (A), or in the presence of 10 μM (B), 20 μM (C) and 50 μM (D) sertraline as indicated at the top of each panel. [Mg²⁺]_i was measured continuously (0.2 s intervals) and smoothed with adjacent averaging of 51 data points (red lines). Black and blue lines were drawn by the least-squares fit to unsmoothed data points. Relative Mg²⁺-efflux rates (shown near the traces) were corrected by initial [Mg²⁺]_i (see Methods) and calculated from these slopes.

Fig. 3

The effect of sertraline on Mg²⁺ influx. [Mg²⁺]_i of Mg²⁺-depleted cells (mean ± SD) was plotted as a function of time, in the Ca²⁺-free Tyrode’s solution in the absence (A, n = 5) or in the presence of 50 μM sertraline (B, n = 5). The red solid line is a single exponential function with mean values of the parameters obtained from each experiment (see Methods).

Fig. 4

Sertraline concentration vs. Mg²⁺ efflux inhibition. Relative Mg²⁺ efflux rates obtained in each cell (■) and their mean ± SD values (□) were plotted as a function of sertraline concentration. The solid line indicates the least-squares fit of the data sets (■) by the Hill-type curve, [Relative Mg²⁺ efflux rate] = 1 − [X]^N/([IC₅₀]^N +[X]^N), defined as the maximum value of 1 and the minimum value (R_min) ≥ 0. [X] is sertraline concentration and N is the Hill coefficient. Relative Mg²⁺ efflux rates after washout of sertraline obtained in each cell (×) and their mean ± SD values (○) were also plotted. The dashed line was drawn by the least-squares fit of the data sets (×) in the same manner as described above for the solid line.

Fig. 5

Comparison of the inhibitory effects of selective serotonin reuptake inhibitors (SSRIs). A, Relative Mg²⁺ efflux rates obtained in the presence of 20 μM of sertraline (■), paroxetine (▲), or fluvoxamine (●) were plotted together with mean ± SD values (bars). *p < 0.05 (Mann-Whitney U-test), B, Fluvoxamine concentration-response curve. Relative Mg²⁺ efflux rates obtained in each cell (•) and their mean ± SD values (○) were plotted against fluvoxamine concentration on the abscissa. The solid line indicates the Hill-type fitting curve analyzed in the same manner as described in Fig. 4 legend.