Imipramine, mianserine and maprotiline block delayed rectifier potassium current in ventricular myocytes

Investigating the Impact of Selective Modulators on the Renin-Angiotensin-Aldosterone System: Unraveling Their Off-Target Perturbations of Transmembrane Ionic Currents

The renin-angiotensin-aldosterone system (RAAS) plays a crucial role in maintaining various physiological processes in the body, including blood pressure regulation, electrolyte balance, and overall cardiovascular health. However, any compounds or drugs known to perturb the RAAS might have an additional impact on transmembrane ionic currents. In this retrospective review article, we aimed to present a selection of chemical compounds or medications that have long been recognized as interfering with the RAAS. It is noteworthy that these substances may also exhibit regulatory effects in different types of ionic currents. Apocynin, known to attenuate the angiotensin II-induced activation of epithelial Na+ channels, was shown to stimulate peak and late components of voltage-gated Na+ current (INa). Esaxerenone, an antagonist of the mineralocorticoid receptor, can exert an inhibitory effect on peak and late INa directly. Dexamethasone, a synthetic glucocorticoid, can directly enhance the open probability of large-conductance Ca2+-activated K+ channels. Sparsentan, a dual-acting antagonist of the angiotensin II receptor and endothelin type A receptors, was found to suppress the amplitude of peak and late INa effectively. However, telmisartan, a blocker of the angiotensin II receptor, was effective in stimulating the peak and late INa along with a slowing of the inactivation time course of the current. However, telmisartan's presence can also suppress the erg-mediated K+ current. Moreover, tolvaptan, recognized as an aquaretic agent that can block the vasopressin receptor, was noted to suppress the amplitude of the delayed-rectifier K+ current and the M-type K+ current directly. The above results indicate that these substances not only have an interference effect on the RAAS but also exert regulatory effects on different types of ionic currents. Therefore, to determine their mechanisms of action, it is necessary to gain a deeper understanding.

Evidence for Effective Multiple K+-Current Inhibitions by Tolvaptan, a Non-peptide Antagonist of Vasopressin V2 Receptor

Tolvaptan (TLV), an oral non-peptide antagonist of vasopressin V₂ receptor, has been increasingly used for managements in patients with hyponatremia and/or syndrome of inappropriate antidiuretic hormone secretion. However, none of the studies have thus far been investigated with regard to its possible perturbations on membrane ion currents in endocrine or neuroendocrine cells. In our electrophysiological study, the whole-cell current recordings showed that the presence of TLV effectively and differentially suppressed the amplitude of delayed rectifier K⁺ (I_K(DR)) and M-type K⁺ current (I_K(M)) in pituitary GH₃ cells with an IC₅₀ value of 6.42 and 1.91 μM, respectively. This compound was also capable of shifting the steady-state activation curve of I_K(M) to less depolarized potential without any appreciable change in the gating charge of this current. TLV at a concentration greater than 10 μM also suppressed the amplitude of erg-mediated K⁺ current or the activity of large-conductance Ca²⁺-activated K⁺ channels; however, this compound failed to alter the amplitude of hyperpolarization-activated cation current in GH₃ cells. In vasopressin-preincubated GH₃ cells, TLV-mediated suppression of I_K(M) remained little altered. Under current-clamp condition, we also observed that addition of TLV increased the firing of spontaneous action potentials in GH₃ cells and further addition of flupirtine could reverse TLV-mediated elevation of the firing. In Madin-Darby canine kidney (MDCK) cells, the K⁺ current elicited by long ramp pulse was also effectively subject to inhibition by this compound. Findings from the present study were thus stated as saying that the suppression by TLV of multiple type K⁺ currents could be direct and independent of its antagonism of vasopressin V₂ receptors. Our study also reveals an important aspect that should be considered when assessing aquaretic effect of TLV or its structurally similar compounds.

Effect of glibenclamide on antinociceptive effects of antidepressants of different classes

OBJECTIVES

The purpose of this work was to determine whether the intraperitoneal administration of glibenclamide as a K ATP channel blocker could have an effect on the antinociceptive effects of antidepressants with different mechanisms of action.

METHODS

Three antidepressant drugs, amitriptyline as a dual-action, nonselective inhibitor of noradrenaline and a serotonin reuptake inhibitor, fluvoxamine as a selective serotonin reuptake inhibitor and maprotiline as a selective noradrenaline reuptake inhibitor, were selected, and the effect of glibenclamide on their antinociceptive activities was assessed in male Swiss mice (25-30 g) using a formalin test.

DISCUSSION

None of the drugs affected acute nociceptive responses during the first phase. Amitriptyline (5, 10 mg/ kg), maprotiline (10, 20 mg/kg) and fluvoxamine (20 and 30 mg/kg) effectively inhibited pain induction caused by the second phase of the formalin test. Glibenclamide (5 mg/kg) alone did not alter licking behaviors based on a comparison with the control group. However, the pretreatment of animals with glibenclamide (10 and 15 mg/kg) partially reversed the antinociceptive effects of fluvoxamine but not those of maprotiline. In addition, the highest dose of glibenclamide (15 mg/kg) partially prevented the analgesic effect of amitriptyline.

CONCLUSION

Therefore, it seems that adenosine triphosphate-dependent potassium channels have a major role in the analgesic activity of amitriptyline and fluvoxamine.

Mianserin and Ventricular Tachycardia: Case Report and Review of the Literature

Mianserin is a drug frequently used to treat depression and sleep disturbances. Despite documented effects on various cardiac tissues in animal studies, mianserin has a very safe clinical profile. Only one case of ventricular arrhythmias in a patient treated with mianserin has been reported. This patient had a severe cardiac history. Our case is to our knowledge the first report on ventricular arrhythmias in a patient treated with mianserin without previous or present cardiac disease. After discontinuation of mianserin the arrhythmias disappeared within days. The literature on mianserin toxicity is reviewed.

Blockade of calcium entry in smooth muscle cells by the antidepressant imipramine

The present study was designed to evaluate the effects of antidepressants on smooth muscle contractile activity. In rat aortic rings, the antidepressants imipramine, mianserin and sertraline provoked concentration-dependent inhibitions of the mechanical responses evoked by K+ (30 mM) depolarization. These myorelaxant effects were not modified by the presence of glibenclamide or 80 mM K+ in the bathing medium. Moreover, the vasodilator properties of imipramine were not affected by atropine, phentolamine and pyrilamine. Radioisotopic experiments indicated that imipramine failed to enhance 86Rb outflow from prelabelled and perifused aortic rings whilst counteracting the increase in 45Ca outflow provoked by a rise in the extracellular K+ concentration. Simultaneous measurements of contractile activity and fura-2 fluorescence revealed that, in aortic rings, imipramine reduced the mechanical and fluorimetric response to K+ challenge. In A7r5 smooth muscle cells, whole cell recordings further demonstrated that imipramine inhibited the inward Ca2+ current. Under different experimental conditions, the ionic and relaxation responses to the antidepressants were reminiscent of those mediated by the Ca2+ entry blocker verapamil. Lastly, it should be pointed out that imipramine exhibited a myorelaxant effect of similar amplitude on rat aorta and on rat distal colon. All together, these findings suggest that the myorelaxant properties of imipramine, and probably also setraline and mianserin, could result from their capacity to inhibit the voltage-sensitive Ca2+ channels.

Effect of maprotiline on Ca2+ movement in human neuroblastoma cells

In human neuroblastoma IMR32 cells, the effect of the anti-depressant maprotiline on baseline intracellular Ca2+ concentrations ([Ca2+]i) was explored by using the Ca2+-sensitive probe fura-2. Maprotiline at concentrations greater than 100 microM caused a rapid rise in [Ca2+]i in a concentration-dependent manner (EC50 = 200 microM). Maprotiline-induced [Ca2+]i rise was reduced by 50% by removal of extracellular Ca2+. Maprotiline-induced [Ca2+]i rises were inhibited by half by nifedipine, but was unaffected by verapamil or diiltiazem. In Ca2+-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+-ATPase, caused a monophasic [Ca2+]i rise, after which the increasing effect of maprotiline on [Ca2+]i was abolished. U73122, an inhibitor of phospholipase C, did not affect maprotiline-induced [Ca2+]i rises. These findings suggest that in human neuroblastoma cells, maprotiline increases [Ca2+]i by stimulating extracellular Ca2+ influx and also by causing intracellular Ca2+ release from the endoplasmic reticulum via a phospholiase C-independent manner.

EFFECT OF THE ANTIDEPRESSANT MAPROTILINE ON CA2+ MOVEMENT AND PROLIFERATION IN HUMAN PROSTATE CANCER CELLS

1. The effect of maprotiline, an antidepressant, on human prostate cells is unclear. In the present study, the effect of maprotiline on [Ca2+]i and growth in PC3 human prostate cancer cells was measured using the fluorescent dyes fura-2 and tetrazolium, respectively. 2. Maprotiline caused a rapid, concentration-dependent increase in [Ca2+]i (EC50 = 200 micromol/L). The maprotiline-induced [Ca2+]i increase was reduced by removal of extracellular Ca2+ or pretreatment with nicardipine. 3. The maprotiline-induced Mn2+ influx-associated fura-2 fluorescence quench directly suggests that maprotiline caused Ca2+ influx. 4. In Ca(2+)-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca(2+)-ATPase, caused a monophasic [Ca2+]i increase, after which the effects of maprotiline of increasing [Ca2+]i were abolished. In addition, pretreatment with maprotiline reduced a major portion of the thapsigargin-induced increase in [Ca2+]i. 5. U73122, an inhibitor of phospholipase C, abolished the ATP (but not maprotiline)-induced increase in [Ca2+]i. 6. Overnight incubation with 1-10 micromol/L maprotiline did not alter cell proliferation, although incubation with 30-50 micromol/L maprotiline decreased cell proliferation. 7, These findings suggest that maprotiline rapidly increases [Ca2+]i in human prostate cancer cells by stimulating both extracellular Ca2+ influx and intracellular Ca2+ release and that it may modulate cell proliferation in a concentration-dependent manner.