Post-SSRI Sexual Dysfunction: A Bioelectric Mechanism?

Selective serotonin reuptake inhibitor (SSRI) drugs, targeting serotonin transport, are widely used. A puzzling and biomedically important phenomenon concerns the persistent sexual dysfunction following SSRI use seen in some patients. What could be the mechanism of a persistent physiological state brought on by a transient exposure to serotonin transport blockers? In this study, we briefly review the clinical facts concerning this side effect of serotonin reuptake inhibitors and suggest a possible mechanism. Bioelectric circuits (among neural or non-neural cells) could persistently maintain alterations of bioelectric cell properties (resting potential), resulting in long-term changes in electrophysiology and signaling. We present new data revealing this phenomenon in planarian flatworms, in which brief SSRI exposures induce long-lasting changes in resting potential profile. We also briefly review recent data linking neurotransmitter signaling to developmental bioelectrics. Further study of tissue bioelectric memory could enable the design of ionoceutical interventions to counteract side effects of SSRIs and similar drugs.

Inhibition of the Voltage-Dependent K+ Current by the Tricyclic Antidepressant Desipramine in Rabbit Coronary Arterial Smooth Muscle Cells

We describe the effect of a tricyclic antidepressant drug desipramine on voltage-dependent K⁺ (Kv) currents in freshly isolated rabbit coronary arterial smooth muscle cells using a conventional whole-cell patch clamp technique. Application of desipramine rapidly decreased the Kv current amplitude in a concentration-dependent manner, with an IC₅₀ value of 5.91 ± 0.18 μM and a Hill coefficient of 0.61 ± 0.09. The steady-state inactivation curves of the Kv channels were not affected by desipramine. However, desipramine shifted the steady-state inactivation curves toward a more negative potential. Application of train pulses (1 or 2 Hz) slightly reduced the Kv current amplitude. Such reduction in the Kv current amplitude by train pulses increased in the presence of desipramine. Furthermore, the inactivation recovery time constant was also increased in the presence of desipramine, suggesting that desipramine-induced inhibition of the Kv current was use-dependent. Application of a Kv1.5 inhibitor (DPO-1) and/or a Kv2.1 inhibitor (guangxitoxin) did not change the inhibitory effect of desipramine on Kv currents. Based on these results, we concluded that desipramine directly inhibited the Kv channels in a dose- and state-dependent manner, but the effect was independent of norepinephrine/serotonin reuptake inhibition.

Blockade of voltage-dependent K+ current in rabbit coronary arterial smooth muscle cells by the tricyclic antidepressant clomipramine

We investigated the effect of the tricyclic antidepressant clomipramine on voltage-dependent K⁺ (Kv) channels in native rabbit coronary arterial smooth muscle cells. Our results showed that clomipramine inhibited vascular Kv channels in a concentration-dependent manner, with an IC₅₀ value of 8.61 ± 4.86 μM and a Hill coefficient (n) of 0.58 ± 0.07. The application of 10 μM clomipramine did not affect the activation curves of the Kv channels; however, the inactivation curves of the Kv channels were shifted toward a more negative potential. The clomipramine-induced inhibition of Kv currents was not changed by the application of train pulses (1 or 2 Hz), which demonstrated that clomipramine inhibited Kv current in a state (use)-independent manner. Pretreatment with the Kv1.5 and Kv2.1 inhibitors, DPO-1 and guangxitoxin, respectively, partially reduced the clomipramine-induced inhibition of Kv currents. Therefore, we concluded that clomipramine inhibited vascular Kv channels in a concentration-dependent, but state (use)-independent manner, regardless of its own function.

Inhibitory effect of the tricyclic antidepressant amitriptyline on voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

Amitriptyline, a tricyclic antidepressant (TCA) drug, is widely used in treatment of psychiatric disorders. However, the side effects of amitriptyline on vascular K⁺ channels remain to be determined. Therefore, we investigated the effect of the tricyclic antidepressant and serotonin reuptake inhibitor amitriptyline on voltage-dependent K⁺ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells, using the whole-cell patch clamp technique. The Kv current amplitudes were inhibited by amitriptyline in a concentration-dependent manner, with an apparent IC₅₀ value of 2.2 ± 0.14 μmol/L and a Hill coefficient of 0.87 ± 0.03. Amitriptyline shifted the activation curve to a more positive potential, but had no significant effect on the inactivation curve, suggesting that amitriptyline altered the voltage sensitivity of Kv channels. Pretreatment with Kv1.5 and Kv1.2 channel inhibitors did not alter the inhibitory effect of amitriptyline on Kv channels. Additionally, application of train pulses (1 and 2 Hz) did not affect amitriptyline-induced inhibition of Kv currents, which suggested that the action of amitriptyline on Kv channels was not use (state)-dependent. From these results, we concluded that amitriptyline inhibited the channels in a concentration-dependent, but state-independent manner.

The selective serotonin reuptake inhibitor dapoxetine inhibits voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

We investigated the inhibitory effect of dapoxetine, a selective serotonin reuptake inhibitor (SSRI), on voltage-dependent K⁺ (Kv) channels using native smooth muscle cells from rabbit coronary arteries. Dapoxetine inhibited Kv channel currents in a concentration-dependent manner, with an IC₅₀ value of 2.68±0.94 μmol/L and a slope value (Hill coefficient) of 0.63±0.11. Application of 10 μmol/L dapoxetine accelerated the rate of inactivation of Kv currents. Although dapoxetine did not modify current activation kinetics, it caused a significant negative shift in the inactivation curves. Application of train step (1 or 2 Hz) progressively increased the inhibitory effect of dapoxetine on Kv channels. In addition, the recovery time constant was extended in its presence, suggesting that the longer recovery time constant from inactivation underlies a use-dependent inhibition of the channel. From these results, we conclude that dapoxetine inhibits Kv channels in a dose-, time-, use-, and state (open)-dependent manner, independent of serotonin reuptake inhibition.

Escitalopram, a selective serotonin reuptake inhibitor, inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells

We investigated the inhibitory effect of escitalopram, a selective serotonin reuptake inhibitor (SSRI), on voltage-dependent K⁺ (Kv) channels in freshly separated from rabbit coronary arterial smooth muscle cells. The application of escitalopram rapidly inhibited vascular Kv channels. Kv currents were progressively inhibited by an increase in the concentrations of escitalopram, suggesting that escitalopram inhibited vascular Kv currents in a concentration-dependent manner. The IC₅₀ value and Hill coefficient for escitalopram-induced inhibition of Kv channels were 9.54±1.33 µM and 0.75±0.10, respectively. Addition of escitalopram did not alter the steady-state activation and inactivation curves, suggesting that the voltage sensors of the channels were not affected. Pretreatment with inhibitors of Kv1.5 and/or Kv2.1 did not affect the inhibitory action of escitalopram on vascular Kv channels. From these results, we concluded that escitalopram decreased the vascular Kv current in a concentration-dependent manner, independent of serotonin reuptake inhibition.

Selective serotonin reuptake inhibitor sertraline inhibits voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

We examined the effects of the selective serotonin reuptake inhibitor (SSRI) sertraline on voltage-dependent K+ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells using the voltage-clamp technique. Sertraline decreased the Kv channel current in a dose-dependent manner, with an IC50 value of 0.18 mu M and a slope value (Hill coefficient) of 0.61. Although the application of 1 mu M sertraline did not affect the steady-state activation curves, sertraline caused a significant, negative shift in the inactivation curves. Pretreatment with another SSRI, paroxetine, had no significant effect on Kv currents and did not alter the inhibitory effects of sertraline on Kv currents. From these results, we concluded that sertraline dose-dependently inhibited Kv currents independently of serotonin reuptake inhibition by shifting inactivation curves to a more negative potential.

Nortriptyline, a tricyclic antidepressant, inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells

We demonstrated the effect of nortriptyline, a tricyclic antidepressant drug and serotonin reuptake inhibitor, on voltage-dependent K⁺ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells using a whole-cell patch clamp technique. Nortriptyline inhibited Kv currents in a concentration-dependent manner, with an apparent IC₅₀ value of 2.86±0.52 µM and a Hill coefficient of 0.77±0.1. Although application of nortriptyline did not change the activation curve, nortriptyline shifted the inactivation current toward a more negative potential. Application of train pulses (1 or 2 Hz) did not change the nortriptyline-induced Kv channel inhibition, suggesting that the effects of nortiprtyline were not use-dependent. Preincubation with the Kv1.5 and Kv2.1/2.2 inhibitors, DPO-1 and guangxitoxin did not affect nortriptyline inhibition of Kv channels. From these results, we concluded that nortriptyline inhibited Kv channels in a concentration-dependent and state-independent manner independently of serotonin reuptake.

Cisapride, a selective serotonin 5-HT4-receptor agonist, inhibits voltage-dependent K(+) channels in rabbit coronary arterial smooth muscle cells

We investigated the effect of cisapride, a selective serotonin 5-HT4-receptor agonist, on voltage-dependent K(+) (Kv) channels using freshly isolated smooth muscle cells from the coronary arteries of rabbits. The amplitude of Kv currents was reduced by cisapride in a concentration-dependent manner, with an IC50 value of 6.77 ± 6.01 μM and a Hill coefficient of 0.51 ± 0.18. The application of cisapride shifted the steady-state inactivation curve toward a more negative potential, but had no significant effect on the steady-state activation curve. This suggested that cisapride inhibited the Kv channel in a closed state by changing the voltage sensitivity of Kv channels. The application of another selective serotonin 5-HT4-receptor agonist, prucalopride, did not affect the basal Kv current and did not alter the inhibitory effect of cisapride on Kv channels. From these results, we concluded that cisapride inhibited vascular Kv current in a concentration-dependent manner by shifting the steady-state inactivation curve, independent of its own function as a selective serotonin 5-HT4-receptor agonist.