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

Sigmar1's Molecular, Cellular, and Biological Functions in Regulating Cellular Pathophysiology

The Sigma 1 receptor (Sigmar1) is a ubiquitously expressed multifunctional inter-organelle signaling chaperone protein playing a diverse role in cellular survival. Recessive mutation in Sigmar1 have been identified as a causative gene for neuronal and neuromuscular disorder. Since the discovery over 40 years ago, Sigmar1 has been shown to contribute to numerous cellular functions, including ion channel regulation, protein quality control, endoplasmic reticulum-mitochondrial communication, lipid metabolism, mitochondrial function, autophagy activation, and involved in cellular survival. Alterations in Sigmar1’s subcellular localization, expression, and signaling has been implicated in the progression of a wide range of diseases, such as neurodegenerative diseases, ischemic brain injury, cardiovascular diseases, diabetic retinopathy, cancer, and drug addiction. The goal of this review is to summarize the current knowledge of Sigmar1 biology focusing the recent discoveries on Sigmar1’s molecular, cellular, pathophysiological, and biological functions.

The effects of tegaserod, a gastrokinetic agent, on voltage-gated K+ channels in rabbit coronary arterial smooth muscle cells

Tegaserod, a gastroprokinetic agent, is used to treat irritable bowel syndrome. Despite its extensive clinical use, little is known about the effects of tegaserod on vascular ion channels, especially K+ channels. Therefore, we examined the effects of tegaserod on voltage-gated K+ (Kv) channels in rabbit coronary arterial smooth muscle cells using the whole-cell patch-clamp technique. Tegaserod inhibited Kv channels in a concentration-dependent manner with an IC50 value of 1.26 ± 0.31 µmol/L and Hill coefficient of 0.81 ± 0.10. Although tegaserod had no effect on the steady-state activation curves of the Kv channels, the steady-state inactivation curve was shifted toward a more negative potential. These results suggest that tegaserod inhibits Kv channels by influencing their voltage sensors. The recovery time constant of channel inactivation was extended in the presence of tegaserod. Furthermore, application of train steps (1 and 2 Hz) in the presence of tegaserod progressively increased the inhibition of Kv currents suggesting that tegaserod-induced Kv channel inhibition is use (state)-dependent. Pretreatment with a Kv1.5 subtype inhibitor suppressed the Kv current. However, additional application of tegaserod did not induce further inhibition. Pretreatment with a Kv2.1 or Kv7 inhibitor did not affect the inhibitory effect of tegaserod on Kv channels. Based on these results, we conclude that tegaserod inhibits vascular Kv channels in a concentration- and use (state)-dependent manner independent of its own functions. Furthermore, the major Kv channel target of tegaserod is the Kv1.5 subtype.

Inhibition by the atypical antipsychotic risperidone of voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

We evaluated the inhibitory effects of the atypical antipsychotic drug risperidone on voltage-dependent K⁺ (Kv) channels in rabbit coronary arterial smooth muscle cells. Risperidone suppressed Kv currents in reversible and concentration-dependent manners with an apparent half-maximal effective concentration (IC₅₀ value) of 5.54 ± 0.66 μM and a slope factor of 1.22 ± 0.07. The inactivation of Kv currents was significantly accelerated by risperidone. The rate constants of association and dissociation for risperidone were 0.25 ± 0.01 μM^-1s^-1 and 1.36 ± 0.14 s^-1, respectively. Application of risperidone shifted the steady-state activation curve in the positive direction and the inactivation curve in the negative direction, suggesting that the risperidone-induced inhibition of Kv channels was mediated by effects on the voltage sensors of the channels. Application of train pulses at 1 and 2 Hz led to a progressive increase in the blockage of Kv currents by risperidone. In addition, the recovery time constants from inactivation were extended in the presence of risperidone, indicating that risperidone inhibited Kv channels in a use (state)-dependent manner. Pretreatment with the Kv1.5 subtype inhibitor reduced the inhibitory effects of risperidone on Kv channels. However, pretreatment with a Kv2.1 or Kv7.X subtype inhibitor did not affect the inhibitory effects of risperidone. Risperidone induced vasoconstriction and membrane depolarization. Based on these results, we conclude that risperidone inhibits Kv channels in a concentration-, time-, and state-dependent manners. Our results should be taken into consideration when using risperidone to study the kinetics of K⁺ channels in vascular smooth muscle.

Selective serotonin reuptake inhibitors ameliorate MEGF10 myopathy

MEGF10 myopathy is a rare inherited muscle disease that is named after the causative gene, MEGF10. The classic phenotype, early onset myopathy, areflexia, respiratory distress and dysphagia, is severe and immediately life-threatening. There are no disease-modifying therapies. We performed a small molecule screen and follow-up studies to seek a novel therapy. A primary in vitro drug screen assessed cellular proliferation patterns in Megf10-deficient myoblasts. Secondary evaluations were performed on primary screen hits using myoblasts derived from Megf10-/- mice, induced pluripotent stem cell-derived myoblasts from MEGF10 myopathy patients, mutant Drosophila that are deficient in the homologue of MEGF10 (Drpr) and megf10 mutant zebrafish. The screen yielded two promising candidates that are both selective serotonin reuptake inhibitors (SSRIs), sertraline and escitalopram. In depth follow-up analyses demonstrated that sertraline was highly effective in alleviating abnormalities across multiple models of the disease including mouse myoblast, human myoblast, Drosophila and zebrafish models. Sertraline also restored deficiencies of Notch1 in disease models. We conclude that SSRIs show promise as potential therapeutic compounds for MEGF10 myopathy, especially sertraline. The mechanism of action may involve the Notch pathway.

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.

Inhibitory Effect of Tricyclic Antidepressant Doxepin on Voltage-Dependent K+ Channels in Rabbit Coronary Arterial Smooth Muscle Cells

Doxepin, tricyclic antidepressant, is widely used for the treatment of depressive disorders. Our present study determined the inhibitory effect of doxepin on voltage-dependent K⁺ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells using a whole-cell patch clamp technique. Vascular Kv currents were inhibited by doxepin in a concentration-dependent manner, with a half-maximal inhibitory concentration (IC₅₀) value of 6.52 ± 1.35 μM and a Hill coefficient of 0.72 ± 0.03. Doxepin did not change the steady-state activation curve or inactivation curve, suggesting that doxepin does not alter the gating properties of Kv channels. Application of train pulses (1 or 2 Hz) slightly reduced the amplitude of Kv currents. However, the inhibition of Kv channels by train pulses were not changed in the presence of doxepin. Pretreatment with Kv1.5 inhibitor, DPO-1, effectively reduced the doxepin-induced inhibition of the Kv current. However, pretreatment with Kv2.1 inhibitor (guangxitoxin) or Kv7 inhibitor (linopirdine) did not change the inhibitory effect of doxepin on Kv currents. Inhibition of Kv channels by doxepin caused vasoconstriction and membrane depolarization. Therefore, our present study suggests that doxepin inhibits Kv channels in a concentration-dependent, but not use-, and state-dependent manners, irrespective of its own function.

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.

Cardiac Dysfunction in the Sigma 1 Receptor Knockout Mouse Associated With Impaired Mitochondrial Dynamics and Bioenergetics

Background The Sigma 1 receptor (Sigmar1) functions as an interorganelle signaling molecule and elicits cytoprotective functions. The presence of Sigmar1 in the heart was first reported on the basis of a ligand-binding assay, and all studies to date have been limited to pharmacological approaches using less-selective ligands for Sigmar1. However, the physiological function of cardiac Sigmar1 remains unknown. We investigated the physiological function of Sigmar1 in regulating cardiac hemodynamics using the Sigmar1 knockout mouse (Sigmar1-/-). Methods and Results Sigmar1-/- hearts at 3 to 4 months of age showed significantly increased contractility as assessed by left ventricular catheterization with stimulation by increasing doses of a β1-adrenoceptor agonist. Noninvasive echocardiographic measurements were also used to measure cardiac function over time, and the data showed the development of cardiac contractile dysfunction in Sigmar1 -/- hearts as the animals aged. Histochemistry demonstrated significant cardiac fibrosis, collagen deposition, and increased periostin in the Sigmar1 -/- hearts compared with wild-type hearts. Ultrastructural analysis of Sigmar1-/- cardiomyocytes revealed an irregularly shaped, highly fused mitochondrial network with abnormal cristae. Mitochondrial size was larger in Sigmar1-/- hearts, resulting in decreased numbers of mitochondria per microscopic field. In addition, Sigmar1-/- hearts showed altered expression of mitochondrial dynamics regulatory proteins. Real-time oxygen consumption rates in isolated mitochondria showed reduced respiratory function in Sigmar1-/- hearts compared with wild-type hearts. Conclusions We demonstrate a potential function of Sigmar1 in regulating normal mitochondrial organization and size in the heart. Sigmar1 loss of function led to mitochondrial dysfunction, abnormal mitochondrial architecture, and adverse cardiac remodeling, culminating in cardiac contractile dysfunction.

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.

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.