Risperidone inhibits contractions induced by serotonin and histamine and reduces K+ currents in smooth muscle of human umbilical artery

Impact of plasma 5-hydroxyindoleacetic acid, a serotonin metabolite, on clinical outcome in septic shock, and its effect on vascular permeability

Septic shock is characterized by dysregulated vascular permeability. We hypothesized that the vascular permeability of endothelial cells (ECs) would be regulated by serotonin via serotonin-Rho-associated kinase (ROCK) signaling. We aimed to determine the impact of 5-hydroxyindoleacetic acid (5-HIAA) on septic shock as a novel biomarker. Plasma 5-HIAA levels and disease severity indices were obtained from 47 patients with sepsis. The association between 5-HIAA levels and severity indices was analyzed. Permeability upon serotonin stimulation was determined using human pulmonary microvascular ECs. 5-HIAA were significantly higher in septic shock patients than in patients without shock or healthy controls (p = 0.004). These elevated levels were correlated with severity indexes (SOFA score [p < 0.001], APACHE II [p < 0.001], and PaO₂:FiO₂ [p = 0.02]), and longitudinally associated with worse clinical outcomes (mechanical ventilation duration [p = 0.009] and ICU duration [p = 0.01]). In the experiment, serotonin increased the permeability of ECs, which was inhibited by the ROCK inhibitor (p < 0.001). Serotonin increases vascular permeability of ECs via ROCK signaling. This suggests a novel mechanism by which serotonin disrupts endothelial barriers via ROCK signaling and causes the pathogenesis of septic shock with a vascular leak. Serotonin serves as a novel biomarker of vascular permeability.

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.

Extracellular ATP induces fast and transient non-selective cationic currents and cytosolic Ca2+ changes in human umbilical artery smooth muscle cells

Ionotropic purinergic receptors (P2X) are expressed in endothelial and smooth muscle cells of blood vessels. ATP acting on smooth muscle P2X receptors is able to induce vasoconstriction in different kind of vessels. However, to our knowledge, there are no reports that directly show the activity of these purinergic receptors in native human vascular smooth muscle cells. In this work, we describe for the first time an ATP-induced current in freshly isolated human umbilical artery (HUA) smooth muscle cells. The current was measured by patch-clamp technique in whole-cell condition on cells clamped at -50 mV. At 100 μM of ATP the current showed a rapid activation and desensitization, and was carried by both Na(+) and Ca(2+). The current was completely blocked by suramin (300 μM) and partially blocked by 100 μM of Zn(2+) without affecting the kinetic of desensitization. All these properties suggest that the ATP-induced ionic currents are mediated through P2X(1)-like receptors. Moreover, we show that ATP transiently increased cytosolic Ca(2+) in "in situ" smooth muscle cells of intact HUA segments and that this response is dependent of extracellular and intracellular Ca(2+). These data expand the knowledge of purinergic receptors properties in vascular smooth muscle cells and the probable role of ATP as a paracrine modulator of contractile tone in a human artery which is fundamental for feto-placental blood flow.