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.

The inhibitory effect of ziprasidone on voltage-dependent K+ channels in coronary arterial smooth muscle cells.

We investigated the effect of ziprasidone, a widely used treatment for schizophrenia, on voltage-dependent K+ (Kv) channels of coronary arterial smooth muscle cells using the patch-clamp technique. Ziprasidone dose-dependently inhibited Kv channels with an IC50 value of 0.39 ± 0.06 µM and a Hill coefficient of 0.62 ± 0.03. Although ziprasidone had no effect on the steady-state inactivation kinetics of the Kv channels, the steady-state activation curve shifted towards a more positive potential. These results suggest that ziprasidone inhibits Kv channels by targeting their voltage sensors. The recovery time constant of Kv channel inactivation was increased in the presence of ziprasidone. Furthermore, application of train steps (of 1 and 2 Hz) in the presence of ziprasidone led to a progressive increase in the blockade of Kv currents, suggesting that ziprasidone-induced inhibition of Kv channels is use (state)-dependent. Pretreatment with Kv1.5, Kv2.1, and Kv7 subtype inhibitors partially suppressed the ziprasidone-induced inhibition of Kv currents. These results suggest that ziprasidone inhibits vascular Kv channels through its effect on gating properties. The Kv channel-inhibiting action of ziprasidone is concentration- and use (state)-depedent.

Empagliflozin dilates the rabbit aorta by activating PKG and voltage-dependent K+ channels.

We investigated the vasodilatory effects of empagliflozin (a sodium-glucose co-transporter 2 inhibitor) and the underlying mechanisms using rabbit aorta. Empagliflozin induced vasodilation in a concentration-dependent manner independently of the endothelium. Likewise, pretreatment with the nitric oxide synthase inhibitor L-NAME or the SKca inhibitor apamin together with the IKca inhibitor TRAM-34 did not impact the vasodilatory effects of empagliflozin. Pretreatment with the adenylyl cyclase inhibitor SQ22536 or a guanylyl cyclase inhibitor ODQ or a protein kinase A (PKA) inhibitor KT5720 also did not alter the vasodilatory response of empagliflozin. However, the vasodilatory effects of empagliflozin were significantly reduced by pretreatment with the protein kinase G (PKG) inhibitor KT5823. Although application of the ATP-sensitive K+ (KATP) channel inhibitor glibenclamide, large-conductance Ca2+-activated K+ (BKCa) channel inhibitor paxilline, or inwardly rectifying K+ (Kir) channel inhibitor Ba2+ did not impact the vasodilatory effects of empagliflozin, pretreatment with the voltage-dependent K+ (Kv) channel inhibitor 4-AP reduced the vasodilatory effects of empagliflozin. Pretreatment with DPO-1 (Kv1.5 channel inhibitor), guangxitoxin (Kv2.1 channel inhibitor), or linopirdine (Kv7 channel inhibitor) had little effect on empagliflozin-induced vasodilation. Application of nifedipine (L-type Ca2+ channel inhibitor) or thapsigargin (sarco-endoplasmic reticulum Ca2+-ATPase pump inhibitor) did not impact empagliflozin-induced vasodilation. Therefore, empagliflozin induces vasodilation by activating PKG and Kv channels.

Inhibition of voltage-dependent K+ channels by iloperidone in coronary arterial smooth muscle cells.

Iloperidone, a second-generation atypical antipsychotic drug, is widely used in the treatment of schizophrenia. However, the side-effects of iloperidone on vascular K+ channels remain to be determined. Therefore, we explored the effect of iloperidone on voltage-dependent K+ (Kv) channels in rabbit coronary arterial smooth muscle cells using the whole-cell patch-clamp technique. Iloperidone inhibited vascular Kv channels in a concentration-dependent manner with a half-maximal inhibitory concentration (IC50 ) of 2.11 ± 0.5 µM and a Hill coefficient of 0.68 ± 0.03. Iloperidone had no effect on the steady-state inactivation kinetics. However, it shifted the steady-state activation curve to the right, indicating that iloperidone inhibited Kv channels by influencing the voltage sensors. Application of 20 repetitive depolarizing pulses (1 and 2 Hz) progressively increased the inhibition of the Kv current in the presence of iloperidone. Furthermore, iloperidone increased the recovery time constant from Kv channel inactivation, suggesting that iloperidone-induced inhibition of Kv channels is use (state)-dependent. Pretreatment with a Kv1.5 inhibitor (diphenyl phosphine oxide 1 [DPO-1]) inhibited the Kv current to a level similar to that with iloperidone alone. However, pretreatment with a Kv2.1 or Kv7.X inhibitor (guangxitoxin or linopirdine) did not affect the inhibitory effect of iloperidone on Kv channels. Therefore, iloperidone directly inhibits Kv channels in a concentration- and use (state)-dependent manner independently of its antagonism of serotonin and dopamine receptors. Furthermore, the primary target of iloperidone is the Kv1.5 subtype.

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.

Dipeptidyl peptidase-4 inhibitor sitagliptin induces vasorelaxation via the activation of Kv channels and PKA.

The present study investigated the vasorelaxant effects of sitagliptin, which is a dipeptidyl peptidase-4 (DPP-4) inhibitor in aortic rings pre-contracted with phenylephrine (Phe). Sitagliptin induced vasorelaxation in a concentration-dependent manner but the inhibition of voltage-dependent K+ (Kv) channels by pretreatment with 4-aminopyridine (4-AP) effectively reduced this effect. By contrast, the inhibition of inward rectifier K+ (Kir) channels by pretreatment with barium (Ba2+), large-conductance calcium (Ca2+)-activated K+ (BKCa) channels with paxilline, and adenosine triphosphate (ATP)-sensitive K+ (KATP) channels with glibenclamide did not change this effect. Although the application of SQ 22536, which is an adenylyl cyclase inhibitor, also did not change this effect, treatment with KT 5720, a protein kinase A (PKA) inhibitor, effectively reduced the vasorelaxant effects of sitagliptin. ODQ, which is a guanylyl cyclase inhibitor, and KT 5823, a protein kinase G (PKG) inhibitor, did not impact the effect. Furthermore, neither the inhibition of Ca2+ channels by pretreatment with nifedipine nor the inhibition of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) pumps by pretreatment with thapsigargin changed the effect. Similarly, the effects of sitagliptin were not altered by eliminating the endothelium, by pretreatment with a nitric oxide (NO) synthase inhibitor (L-NAME), or by inhibition of small- and intermediate-conductance Ca2+-activated K+ channels (SKCa and IKCa) using apamin and TRAM-34. Taken together, these results suggest that sitagliptin induces vasorelaxation by inhibiting both membrane potential (Em)-dependent and -independent vasoconstriction and activating PKA and Kv channels independently of PKG signaling pathways, other K+ channels, SERCA pumps, and the endothelium.

The anticholinergic drug oxybutynin inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells.

This study demonstrates the inhibitory effect of anticholinergic drug oxybutynin on voltage-dependent K+ (Kv) channels in rabbit coronary arterial smooth muscle cells. Oxybutynin inhibited vascular Kv channels in a concentration-dependent manner, with an IC50 value of 11.51 ± 0.38 µmol/L and a Hill coefficient (n) of 2.25 ± 0.12. Application of oxybutynin shifted the activation curve to the right and the inactivation curve to the left. Pretreatment with the Kv1.5 subtype inhibitor DPO-1 and the Kv2.1 subtype inhibitor guangxitoxin suppressed the oxybutynin-induced inhibition of the Kv current. However, application of the Kv7 subtype inhibitor linopirdine did not affect the inhibition by oxybutynin of the Kv current. The anticholinergic drug atropine did not inhibit the Kv current nor influence oxybutynin-induced inhibition of the Kv current. From these results, we concluded that oxybutynin inhibited the vascular Kv current in a concentration-dependent manner by influencing the steady-state activation and inactivation curves independent of its anticholinergic effect.

Atypical antipsychotic olanzapine inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells.

BACKGROUND: Olanzapine, an FDA-approved atypical antipsychotic, is widely used to treat schizophrenia and bipolar disorder. In this study, the inhibitory effect of olanzapine on voltage-dependent K+ (Kv) channels in rabbit coronary arterial smooth muscle cells was investigated. METHODS: Electrophysiological recordings were performed in freshly isolated coronary arterial smooth muscle cells. RESULTS: Olanzapine inhibited the Kv channels in a concentration-dependent manner with an IC50 value of 7.76 ± 1.80 µM and a Hill coefficient of 0.82 ± 0.09. Although olanzapine did not change the steady-state activation curve, it shifted the inactivation curve to a more negative potential, suggesting that it inhibited Kv currents by affecting the voltage sensor of the Kv channel. Application of 1 or 2 Hz train pulses did not affect the olanzapine-induced inhibition of Kv channels, suggesting that its effect on Kv channels occurs in a use (state)-independent manner. Pretreatment with DPO-1 (Kv1.5 subtype inhibitor) reduced the olanzapine-induced inhibition of Kv currents. In addition, pretreatment with guangxitoxin (Kv2.1 subtype inhibitor) and linopirdine (Kv7 subtype inhibitor) partially decreased the degree of Kv current inhibition. Olanzapine induced membrane depolarization. CONCLUSION: From these results, we suggest that olanzapine inhibits the Kv channels in a concentration-dependent, but state-independent, manner by affecting the gating properties of Kv channels. The primary Kv channel target of olanzapine is the Kv1.5 subtype.

The anti-diabetic drug alogliptin induces vasorelaxation via activation of Kv channels and SERCA pumps.

In the present study, we investigated the vasorelaxant effects of alogliptin, an oral antidiabetic drug in the dipeptidyl peptidase-4 (DPP-4) inhibitor class, using phenylephrine (Phe)-induced pre-contracted aortic rings. Alogliptin induced vasorelaxation in a dose-dependent manner. Pre-treatment with the voltage-dependent K+ (Kv) channel inhibitor 4-aminopyridine (4-AP) significantly decreased the vasorelaxant effect of alogliptin, whereas pre-treatment with the inwardly rectifying K+ (Kir) channel inhibitor Ba2+, ATP-sensitive K+ (KATP) channel inhibitor glibenclamide, and large-conductance Ca2+-activated K+ (BKCa) channel inhibitor paxilline did not alter the effects of alogliptin. Although pre-treatment with the Ca2+ channel inhibitor nifedipine did not affect the vasorelaxant effect of alogliptin, pre-treatment with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid effectively attenuated the vasorelaxant response of alogliptin. Neither cGMP/protein kinase G (PKG)-related signaling pathway inhibitors (guanylyl cyclase inhibitor ODQ and PKG inhibitor KT 5823) nor cAMP/protein kinase A (PKA)-related signaling pathway inhibitors (adenylyl cyclase inhibitor SQ 22536 and PKA inhibitor KT 5720) reduced the vasorelaxant effect of alogliptin. Similarly, the vasorelaxant effect of alogliptin was not changed by endothelium removal or pre-treatment with the nitric oxide (NO) synthase inhibitor L-NAME or the small- and intermediate-conductance Ca2+-activated K+ (SKCa and IKCa) channel inhibitors apamin and TRAM-34. Based on these results, we suggest that alogliptin induced vasorelaxation in rabbit aortic smooth muscle by activating Kv channels and the SERCA pump independent of other K+ channels, cGMP/PKG-related or cAMP/PKA-related signaling pathways, and the endothelium.

Suppression of voltage-gated K+ channels by darifenacin in coronary arterial smooth muscle cells.

Darifenacin, an anticholinergic agent, has been used to treat overactive bladder syndrome. Despite its extensive clinical use, there is little information about the effect of darifenacin on vascular ion channels, specifically K+ channels. This study aimed to investigate the effect of the anti-muscarinic drug darifenacin on voltage-gated K+ (Kv) channels, vascular contractility, and coronary blood flow in rabbit coronary arteries. We used the whole-cell patch-clamp technique to evaluate the effect of darifenacin on Kv channels. Darifenacin inhibited the Kv current in a concentration-dependent manner. Applying 1 µM darifenacin shifted the activation and inactivation curves toward a more positive and negative potential, respectively. Darifenacin slowed the time constants of recovery from inactivation. Furthermore, blockade of the Kv current with darifenacin was increased gradually by applying a train of pulses, indicating that darifenacin inhibited Kv currents in a use- (state)-dependent manner. The darifenacin-mediated inhibition of Kv currents was associated with the Kv1.5 subtype, not the Kv2.1 or Kv7 subtype. Applying another anti-muscarinic drug atropine or ipratropium did not affect the Kv current or change the inhibitory effect of darifenacin. Isometric organ bath experiments using isolated coronary arteries were applied to evaluate whether darifenacin-induced inhibition of the Kv channel causes vasocontraction. Darifenacin substantially induced vasocontraction. Furthermore, darifenacin caused membrane depolarization and decreased coronary blood flow. From these results, we concluded that darifenacin inhibits the Kv currents in concentration- and use- (state)-dependent manners. Inhibition of the Kv current with darifenacin occurred by shifting the steady-state activation and inactivation curves regardless of its anti-muscarinic effect.

Inhibition by Imipramine of the Voltage-Dependent K+ Channel in Rabbit Coronary Arterial Smooth Muscle Cells.

Imipramine, a tricyclic antidepressant, is used in the treatment of depressive disorders. However, the effect of imipramine on vascular ion channels is unclear. Therefore, using a patch-clamp technique we examined the effect of imipramine on voltage-dependent K+ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells. Kv channels were inhibited by imipramine in a concentration-dependent manner, with an IC50 value of 5.55 ± 1.24 µM and a Hill coefficient of 0.73 ± 0.1. Application of imipramine shifted the steady-state activation curve in the positive direction, indicating that imipramine-induced inhibition of Kv channels was mediated by influencing the voltage sensors of the channels. The recovery time constants from Kv-channel inactivation were increased in the presence of imipramine. Furthermore, the application of train pulses (of 1 or 2 Hz) progressively augmented the imipramine-induced inhibition of Kv channels, suggesting that the inhibitory effect of imipramine is use (state) dependent. The magnitude of Kv current inhibition by imipramine was similar during the first, second, and third depolarizing pulses. These results indicate that imipramine-induced inhibition of Kv channels mainly occurs in the closed state. The imipramine-mediated inhibition of Kv channels was associated with the Kv1.5 channel, not the Kv2.1 or Kv7 channel. Inhibition of Kv channels by imipramine caused vasoconstriction. From these results, we conclude that imipramine inhibits vascular Kv channels in a concentration- and use (closed-state)-dependent manner by changing their gating properties regardless of its own function.

Neuron labeling with rhodamine-conjugated Gd-based MRI contrast agents delivered to the brain via focused ultrasound.

Gadolinium-based magnetic resonance imaging contrast agents can provide information regarding neuronal function, provided that these agents can cross the neuronal cell membrane. Such contrast agents are normally restricted to extracellular domains, however, by attaching cationic fluorescent dyes, they can be made cell-permeable and allow for both optical and magnetic resonance detection. To reach neurons, these agents also need to cross the blood-brain barrier. Focused ultrasound combined with microbubbles has been shown to enhance the permeability of this barrier, allowing molecules into the brain non-invasively, locally and transiently. The goal of this study was to investigate whether combining fluorescent rhodamine with a gadolinium complex would form a dual-modal contrast agent that could label neurons in vivo when delivered to the mouse brain with focused ultrasound and microbubbles. Methods: Gadolinium complexes were combined with a fluorescent, cationic rhodamine unit to form probes with fluorescence and relaxivity properties suitable for in vivo applications. The left hemisphere of female C57bl/6 mice (8-10 weeks old; 19.07 ± 1.56 g; n = 16) was treated with ultrasound (centre frequency: 1 MHz, peak-negative pressure: 0.35 MPa, pulse length: 10 ms, repetition frequency: 0.5 Hz) while intravenously injecting SonoVue microbubbles and either the 1 kDa Gd(rhodamine-pip-DO3A) complex or a conventionally-used lysine-fixable Texas Red® 3 kDa dextran. The opposite right hemisphere was used as a non-treated control region. Brains were then extracted and either sectioned and imaged via fluorescence or confocal microscopy or imaged using a 9.4 T magnetic resonance imaging scanner. Brain slices were stained for neurons (NeuN), microglia (Iba1) and astrocytes (GFAP) to investigate the cellular localization of the probes. Results: Rhodamine fluorescence was detected in the left hemisphere of all ultrasound treated mice, while none was detected in the right control hemisphere. Cellular uptake of Gd(rhodamine-pip-DO3A) was observed in all the treated regions with a uniform distribution (coefficient of variation = 0.4 ± 0.05). Uptake was confirmed within neurons, whereas the probe did not co-localize with microglia and astrocytes. Compared to the dextran molecule, Gd(rhodamine-pip-DO3A) distributed more homogeneously and was less concentrated around blood vessels. Furthermore, the dextran molecule was found to accumulate unselectively in microglia as well as neurons, whereas our probe was only taken up by neurons. Gd(rhodamine-pip-DO3A) was detected via magnetic resonance imaging ex vivo in similar regions to where fluorescence was detected. Conclusion: We have introduced a method to image neurons with a dual-modal imaging agent delivered non-invasively and locally to the brain using focused ultrasound and microbubbles. When delivered to the mouse brain, the agent distributed homogeneously and was only uptaken by neurons; in contrast, conventionally used dextran distributed heterogeneously and was uptaken by microglia as well as neurons. This result indicates that our probe labels neurons without microglial involvement and in addition the probe was found to be detectable via both ex vivo MRI and fluorescence. Labeling neurons with such dual-modal agents could facilitate the study of neuronal morphology and physiology using the advantages of both imaging modalities.

The vasodilatory effect of gemigliptin via activation of voltage-dependent K+ channels and SERCA pumps in aortic smooth muscle.

This study investigated the vasodilatory effects and acting mechanism of gemigliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor. Tests were conducted in aortic rings pre-contracted with phenylephrine. Gemigliptin induced dose-dependent vasodilation of the aortic smooth muscle. Several pre-treatment groups were used to investigate the mechanism of action. While pre-treatment with paxilline, a large-conductance Ca2+-activated K+ channel inhibitor, glibenclamide, an ATP-sensitive K+ channel inhibitor, and Ba2+, an inwardly rectifying K+ channel inhibitor, had no impact on the vasodilatory effect of gemigliptin, pre-treatment with 4-aminopyridine, a voltage-dependent K+ (Kv) channel inhibitor, effectively attenuated the vasodilatory action of gemigliptin. In addition, pre-treatment with sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid significantly reduced the vasodilatory effect of gemigliptin. cAMP/PKA-related or cGMP/PKG-related signaling pathway inhibitors, including adenylyl cyclase inhibitor SQ 22536, PKA inhibitor KT 5720, guanylyl cyclase inhibitor ODQ, and PKG inhibitor KT 5823 did not alter the vasodilatory effect of gemigliptin. Similarly, elimination of the endothelium and pre-treatment with a nitric oxide (NO) synthase inhibitor (L-NAME) or small- and intermediate-conductance Ca2+-activated K+ channels (apamin and TRAM-34, respectively) did not change the gemigliptin effect. These findings suggested that gemigliptin induces vasodilation through the activation of Kv channels and SERCA pumps independent of cAMP/PKA-related or cGMP/PKG-related signaling pathways and the endothelium. Therefore, caution is required when prescribing gemigliptin to the patients with hypotension and diabetes.

The muscarinic receptor antagonist tolterodine inhibits voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells.

We explored the effect of the muscarinic receptor antagonist tolterodine on voltage-dependent K+ (Kv) channels using the patch-clamp technique in coronary arterial smooth muscle cells freshly isolated from rabbits. Tolterodine inhibited Kv channels in a concentration-dependent manner, with an IC50 of 1.71 ± 0.33 µM and Hill coefficient of 0.69 ± 0.03. Tolterodine accelerated the decay rate of Kv channel inactivation. The apparent rate constants of association and dissociation for tolterodine were 1.79 ± 0.13 µM-1s-1, and 3.13 ± 0.96 s-1, respectively. Although 3 µM tolterodine had no effect on the steady-state activation of the Kv current, it shifted the steady-state inactivation curve towards a negative potential. Application of consecutive train steps (1 or 2 Hz) progressively decreased the Kv current and promoted its inhibition. Furthermore, the recovery time constant was augmented in the presence of tolterodine, indicating that tolterodine-induced Kv channel blockade is use (state) dependent. Pretreatment with inhibitors of the Kv1.5, Kv2.1, and Kv7 subtypes (DPO-1, guangxitoxin, and linopirdine) partially reduced the inhibitory effect of tolterodine on Kv channels. The alternative muscarinic receptor antagonist atropine did not inhibit the Kv current nor influence tolterodine-induced inhibition of the Kv current. Tolterodine induced vasoconstriction and membrane depolarization. Based on these results, we conclude that tolterodine inhibits Kv channels in concentration-, time-, and use (state)-dependent manners, irrespective of its antagonism of muscarinic receptors.

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.

The vasodilatory effect of the antidiabetic drug linagliptin via inhibition of Rho-associated protein kinase in aortic smooth muscle.

AIMS: The vasodilatory effects of the anti-diabetic drug, linagliptin in phenylephrine-precontracted aortic rings were investigated. MATERIALS AND METHODS: Male New Zealand White rabbits were used in the experiment and its arterial tone was measured by using myogragh system. KEY FINDINGS: Linagliptin induced vasodilation in a concentration-dependent manner. The vasodilatory effect of linagliptin was not affected by the absence of the endothelium, or by pretreatment with a nitric oxide synthase inhibitor (L-NAME) or a small-conductance Ca2+-activated K+ channel inhibitor (apamin). Moreover, application of the adenylyl cyclase inhibitor SQ22536, protein kinase A (PKA) inhibitor KT5720, guanylyl cyclase inhibitor ODQ, or protein kinase G (PKG) inhibitor KT5823 did not alter the vasodilatory effect of linagliptin. However, inhibition of Rho-associated protein kinase by Y-27632 significantly attenuated linagliptin-induced vasodilation. Ion channel involvement in the vasodilatory effect of linagliptin was also investigated. Pretreatment with the vascular K+ channel inhibitors glibenclamide (ATP-sensitive K+ channels), Ba2+ (inwardly rectifying K+ channels), 4-AP (voltage-dependent K+ channels), and paxilline (large conductance Ca2+-activated K+ channels) did not affect linagliptin-induced vasodilation. Furthermore, the L-type Ca2+ channel inhibitor, nifedipine, and the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitor, thapsigargin, did not change the vasodilatory effect of linagliptin. SIGNIFICANCE: We suggests that linagliptin-induced vasodilation was mediated by the inhibition of Rho-associated kinase, but not with the endothelium, cAMP-PKA or cGMP-PKG-dependent signaling pathways, K+ channels, Ca2+ influx, or SERCA pump.

EMG activity and force during prone hip extension in individuals with lumbar segmental instability.

The goal of the current study was to investigate potential differences in back and hip extensor muscle activity and hip extension force during prone hip extension (PHE) in individuals with lumbar segmental instability (LSI) and asymptomatic subjects. Thirty-six subjects with LSI and 26 asymptomatic volunteers participated in this study. Muscle activity of the erector spinae, gluteus maximus, and biceps femoris was recorded using electromyography (EMG), and hip extension force was measured by a digital force gauge. Muscle activity was significantly greater in subjects with LSI than in asymptomatic subjects during PHE (p < 0.05). Hip extension force was significantly lower in the subjects with LSI than in asymptomatic subjects during PHE (p < 0.05). These findings suggest that during PHE, subjects with LSI have differences in back and hip extensor muscle activity and hip extension force compared to asymptomatic individuals.

Effect of the pelvic compression belt on the hip extensor activation patterns of sacroiliac joint pain patients during one-leg standing: a pilot study.

As a means of external stabilization of the sacroiliac joint (SIJ), many clinicians have often advocated the use of the pelvic compression belt (PCB). The objective of this pilot study was to compare the effects of the PCB on hip extensor muscle activation patterns during one-leg standing in subjects with and without sacroiliac joint pain (SIJP). Sixteen subjects with SIJP and fifteen asymptomatic volunteers participated in this study. Surface electromyography (EMG) data [signal amplitude and premotor reaction time (RT)] were collected from the gluteus maximus and biceps femoris muscles of the supporting leg during one-leg standing with and without the PCB. Compared to that of the asymptomatic individuals, the EMG amplitude of the biceps femoris was significantly decreased in individuals with SIJP upon the application of the PCB (p < 0.05). Furthermore, on using the PCB, in individuals with SIJP, the RT of the gluteus maximus was significantly decreased; however, the RT of the biceps femoris was increased (p < 0.05). Thus, our data support the use of the PCB to modify the activation patterns of the hip extensors among patients with SIJP.