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

Modulation of nociception by amitriptyline hydrochloride in the Speke's hinge-back tortoise (Kiniskys spekii)

BACKGROUND

There are limited studies on the utilization of analgesics in testudines. Management of pain in reptiles is by use of analgesics generally used in other vertebrate species. Evidently, some analgesics considered to be generally effective in reptiles are not effective in certain reptile species.

OBJECTIVE

The purpose of this study was to examine the effect of amitriptyline hydrochloride on nociceptive behaviour in Speke's hinge-back tortoise.

METHODS

Twenty-four adult Speke-hinged tortoises weighing 500-700 g were used. The effects of amitriptyline hydrochloride on nociception were evaluated using the formalin, capsaicin and hot plate nociceptive tests. Amitriptyline was administered intracoelomically at doses of 0.5, 1.0 and 3.0 mg/kg.

RESULTS

The higher doses of amitriptyline hydrochloride caused an increase in nociceptive behaviour (time spent in hindlimb withdrawal) on the formalin and capsaicin nociceptive tests, suggesting a potentiating effect. However, the doses used had no significant change in nociceptive behaviour on withdrawal response in the hot plate test.

CONCLUSIONS

The study showed that amitriptyline hydrochloride which is widely used in management of neuropathic pain potentiates nociceptive effects in the formalin and capsaicin nociceptive tests in the Speke's hinge-back tortoise. The hot plate test, which previously has not been reported in these animals, gave results not in line with the other tests and therefore more testing and validation of the test is required. Amitriptyline modulates chemical and thermal pain differently.

Inhibitory effects of antidepressant fluoxetine on cloned Kv2.1 potassium channel expressed in HEK293 cells

It is well demonstrated that antidepressant fluoxetine has significant inhibitory effects on voltage-gated potassium channels. So far, the concise regulation of fluoxetine on Kv2.1, the predominant delayed rectifier potassium channel subtype in the central nervous system, are rarely reported. Here patch-clamp recording was used to investigate the inhibitory effects of fluoxetine on Kv2.1 potassium channels stably expressed in HEK293 cells. The results showed fluoxetine dose-dependently suppressed Kv2.1 currents with an IC₅₀ of 51.3 μM. At the test potential positive to +50 mV, fluoxetine 50 μM voltage-dependently suppressed Kv2.1 currents with an electrical distance δ of 0.28. Moreover, fluoxetine 50 μM did not affect the activation process of Kv2.1, but reduced the decay time constant τ_inact and obviously accelerated the inactivation process of Kv2.1 and left-shifted the half-maximal inactivation potential of Kv2.1 potassium channel by 9.8 mV. Fluoxetine 50 μM notably delayed the recovery process of Kv2.1 from inactivation with increased time constants. In addition, fluoxetine 50 μM use-dependently inhibited Kv2.1 currents at different frequencies. In conclusion, the inhibition of Kv2.1 by fluoxetine was concentration-dependent, voltage-dependent and use-dependent. The accelerated steady-state inactivation of Kv2.1 channels induced by fluoxetine might be ascribed to the delay of the recovery process of Kv2.1.

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.

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

In this study, we explore the inhibitory effects of protriptyline, a tricyclic antidepressant drug, on voltage-dependent K+ (Kv) channels of rabbit coronary arterial smooth muscle cells using a whole-cell patch clamp technique. Protriptyline inhibited the vascular Kv current in a concentration-dependent manner, with an IC50 value of 5.05 ± 0.97 μM and a Hill coefficient of 0.73 ± 0.04. Protriptyline did not affect the steady-state activation kinetics. However, the drug shifted the steady-state inactivation curve to the left, suggesting that protriptyline inhibited the Kv channels by changing their voltage sensitivity. Application of 20 repetitive train pulses (1 or 2 Hz) progressively increased the protriptyline-induced inhibition of the Kv current, suggesting that protriptyline inhibited Kv channels in a use (state)-dependent manner. The extent of Kv current inhibition by protriptyline was similar during the first, second, and third step pulses. These results suggest that protriptyline-induced inhibition of the Kv current mainly occurs principally in the closed state. The increase in the inactivation recovery time constant in the presence of protriptyline also supported use (state)-dependent inhibition of Kv channels by the drug. In the presence of the Kv1.5 inhibitor, protriptyline did not induce further inhibition of the Kv channels. However, pretreatment with a Kv2.1 or Kv7 inhibitor induced further inhibition of Kv current to a similar extent to that observed with protriptyline alone. Thus, we conclude that protriptyline inhibits the vascular Kv channels in a concentration- and use-dependent manner by changing their gating properties. Furthermore, protriptyline-induced inhibition of Kv channels mainly involves the Kv1.5.

Adverse drug reactions associated with amitriptyline - protocol for a systematic multiple-indication review and meta-analysis

BACKGROUND

Unwanted anticholinergic effects are both underestimated and frequently overlooked. Failure to identify adverse drug reactions (ADRs) can lead to prescribing cascades and the unnecessary use of over-the-counter products. The objective of this systematic review and meta-analysis is to explore and quantify the frequency and severity of ADRs associated with amitriptyline vs. placebo in randomized controlled trials (RCTs) involving adults with any indication, as well as healthy individuals.

METHODS

A systematic search in six electronic databases, forward/backward searches, manual searches, and searches for Food and Drug Administration (FDA) and European Medicines Agency (EMA) approval studies, will be performed. Placebo-controlled RCTs evaluating amitriptyline in any dosage, regardless of indication and without restrictions on the time and language of publication, will be included, as will healthy individuals. Studies of topical amitriptyline, combination therapies, or including < 100 participants, will be excluded. Two investigators will screen the studies independently, assess methodological quality, and extract data on design, population, intervention, and outcomes ((non-)anticholinergic ADRs, e.g., symptoms, test results, and adverse drug events (ADEs) such as falls). The primary outcome will be the frequency of anticholinergic ADRs as a binary outcome (absolute number of patients with/without anticholinergic ADRs) in amitriptyline vs. placebo groups. Anticholinergic ADRs will be defined by an experienced clinical pharmacologist, based on literature and data from Martindale: The Complete Drug Reference. Secondary outcomes will be frequency and severity of (non-)anticholinergic ADRs and ADEs. The information will be synthesized in meta-analyses and narratives. We intend to assess heterogeneity using meta-regression (for indication, outcome, and time points) and I2 statistics. Binary outcomes will be expressed as odds ratios, and continuous outcomes as standardized mean differences. Effect measures will be provided using 95% confidence intervals. We plan sensitivity analyses to assess methodological quality, outcome reporting etc., and subgroup analyses on age, dosage, and duration of treatment.

DISCUSSION

We will quantify the frequency of anticholinergic and other ADRs/ADEs in adults taking amitriptyline for any indication by comparing rates for amitriptyline vs. placebo, hence, preventing bias from disease symptoms and nocebo effects. As no standardized instrument exists to measure it, our overall estimate of anticholinergic ADRs may have limitations.

SYSTEMATIC REVIEW REGISTRATION

Submitted to PROSPERO; assignment is in progress.

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.