Human Umbilical Arterial Muscle Research Articles

Risperidone Inhibits Contractions Induced by Serotonin and Histamine and Reduces K+ Currents in Smooth Muscle of Human Umbilical Artery

Risperidone is an antipsychotic commonly used during pregnancy. Because it can cross the placental barrier, our objective was to evaluate its actions on the smooth muscle of the human umbilical artery (HUA). Risperidone preincubation (1-300 nmol/L for 20 minutes) produced a significant decrease in maximum force development induced by serotonin or histamine in HUA rings. When applied on top of stable contractions induced by these agonists risperidone produced quick relaxations (IC(50) = 1 nmol/L for serotonin and 72 nmol/L for histamine). Risperidone induced the contraction of vascular rings depolarized by 40 mmol/L extracellular K(+) but not in the case of 80 mmol/L K(+), suggesting inhibition of K(+) channels. The patch-clamp technique showed that risperidone (3 nmol/L) inhibited whole-cell K(+) currents in freshly isolated HUA smooth muscle cells. Our results are the first showing risperidone effects in human vascular smooth muscle and highlight that its use during pregnancy should be adequately monitored.

Potassium channels in human umbilical artery cells.

To identify K+ channels of smooth muscle of human umbilical artery using the patch-clamp technique and to study their effect on resting tone of umbilical artery rings. Whole-cell and single-channel patch-clamp recordings in enzymatically isolated smooth muscle cells were made. Measurements of developed isometric force were performed on intact tissue. Delayed rectifier K+ channels (KDR) and large-conductance Ca2+-activated K+ channels (BKCa) contribute to the whole-cell voltage- and time-dependent outward K+ current, as it was specifically inhibited by 5 mM 4-aminopyridine (4-AP; KDR blocker) (92 +/- 4% at 0 mV, n = 7), by 1 mM tetraethylammonium (TEA; BKCa blocker) (71 +/- 4% at +60 mV, n = 4), and by 200 nM iberiotoxin (BKCa blocker) (64 +/- 7% at +60 mV, n = 4). In outside-out patches, BKCa channels had a single-channel conductance of 132 +/- 4 pS (n = 24) in asymmetric K+ conditions and 216 +/- 4 pS (n = 4) in a symmetric K+ gradient. The activity of the BKCa channels was significantly augmented by 1 microM Ca2+ in the inside-out configuration. 4-AP had no effect on resting tone of intact arterial rings. TEA produced contraction of arterial rings whereas phloretin, an activator of BKCa, relaxed them, which means that BKCa channels are functional in intact tissue and are involved in the maintenance of resting tone in this human vessel. The identities of K+ channels in the human umbilical artery were shown using the patch-clamp technique, and the physiologic effect of K+ channels on resting tone was documented.

Differential activities of decapeptide agonists of human C5a: the conformational effects of backbone N-methylation

Analogues of the potent, conformationally biased, decapeptide agonist of human C5a anaphylatoxin, C5a 65–74Y65,F67,P69,P71, d-Ala73 (YSFKPMPLaR, peptide 54), were synthesized with methyl groups occupying specific amide nitrogen atoms along the peptide backbone. This N-methylation induced crucial extended backbone conformations in a manner similar to the two Pro residues, but without eliminating the contributions made by the side-chain of the residue for which Pro was substituted. The presence of backbone N-methyl groups on peptide 54 analogues had pronounced detrimental effects on the ability to bind and activate C5aRs expressed on human PMNs, but not on the ability to contract smooth muscle of human umbilical artery. Several N-methylated analogues of peptide 54 (peptides 56, 67, 124, 125, and 137) were significantly more selective for smooth muscle contraction, which is mediated by tissue resident macrophages, than for enzyme release from PMNs. Indeed, peptide 67, YSFKDMP(MeL)aR was almost 3000-fold more selective for smooth muscle contraction than for PMN enzyme release. Consistent with these differential activities was the observation that peptide 67 expressed a significantly greater binding affinity to C5aRs expressed on rat macrophages than on rat PMNs. This differential activity was also observed in vivo in the rat where peptide 67 induced a hypotensive response similar to peptide 54 and rhuC5a, but without accompanying neutropenia.

Vascular reactivity to endothelium-derived relaxing factor in human umbilical artery at term pregnancy

It has been reported that human umbilical artery (HUA) at term pregnancy released endothelium-derived relaxing factor (EDRF), using a superfusion bioassay system. However, other reports showed that endothelium-dependent relaxation was not observed in isometric tension studies using HUA ring with intact endothelium. Thus, we intended to clarify whether vascular smooth muscle of HUA at term is sensitive to EDRF. HUA was obtained after normal vaginal delivery or cesarean section at term. Isometric tension studies were performed in normal Krebs solution, using HUA rings or strips, which were prepared in calcium-free Krebs solution. Sodium nitroprusside (SNP), a nitric oxide (NO) donor drug, relaxed HUA rings precontracted with 0.1 microM 5-hydroxytryptamine (5HT) in a dose-dependent manner (1 nM-10 microM). Histamine, substance P, carbachol, or the calcium ionophore A23187, which are considered to be EDRF-releasing agents, did not relax the HUA rings. By immunohistochemical study, it was confirmed that endothelial cells were present in the luminal surface of the HUA rings after the isometric tension recording. In a co-axial bioassay system involving HUA strips denuded of endothelium and rabbit aorta with intact endothelium, HUA strips precontracted with 0.1 microM 5HT were relaxed in response to 1 microM SNP but not 1 microM carbachol, which released EDRF from the endothelium of rabbit aorta. These findings suggest that HUA at term is sensitive to NO but not EDRF.

Effect of anti-inflammatory drugs on the binding of calcium to cellular membranes in various human and guinea-pig tissues.

1. Cellular membranes were obtained by centrifugation of homogenates of various human and guinea-pig tissues. These membranes took up added calcium (Ca) when incubated at 25 degrees C for 10 min in histidine buffer at pH 7.4. The uptake of Ca was increased by the presence of adenosine triphosphate (ATP).2. Evidence is presented that the membrane fragments which took up Ca under these conditions were derived from the endoplasmic reticulum.3. The ATP-dependent uptake of Ca by membranes derived from guinea-pig aortic or gastric smooth muscle or from human umbilical arterial muscle was inhibited by indomethacin in a concentration-dependent manner.4. The ATP-dependent uptake of Ca by membranes derived from heart, brain, skeletal muscle or liver of the guinea-pig was not inhibited by indomethacin.5. Endothelial cells were obtained from the lining of the human umbilical vein. Cellular membranes were prepared from the endothelial cells by homogenization and centrifugation. The endothelial membranes took up added Ca in the presence of added ATP and this uptake was inhibited by indomethacin and also by members of a group of pharmacologically-related drugs.