h-89 and iberiotoxin

Kaempferol, a flavonoid, is the essential part of human diet. Flavonoids have different pharmacological activities like cardioprotective, anti-inflammatory and anti-oxidant. The aim of current study was to investigate vasorelaxant potential of kaempferol on rat isolated pulmonary artery and to assess the underling mechanisms.. Tension experiments were conducted on both the branches of main pulmonary artery of rats. Experiments were done using isolated organ bath system by recording tension with the help of data acquisition system, Power Lab.. Kaempferol (10. Kaempferol relaxes rat pulmonary artery in endothelium-independent manner through involvement of BK

Topics: Animals; Apamin; Barium Compounds; Calcium Chloride; Chlorides; Dose-Response Relationship, Drug; Endothelium, Vascular; Estradiol; Fulvestrant; Glyburide; In Vitro Techniques; Indomethacin; Isoquinolines; Kaempferols; Male; Morpholines; NG-Nitroarginine Methyl Ester; Oxadiazoles; Peptides; Potassium; Pulmonary Artery; Pyrroles; Quinoxalines; Rats; Sulfonamides; Tetraethylammonium; Vasodilation; Vasodilator Agents

To observe the effect of β₃adrenoceptors (β₃-AR) activation on rat thoracic aorta smooth muscle contractility and the possible related mechanism.. The endothelium removed thoracic aorta was pre-contracted with 30 mmol/L KCl physiological saline solution (PSS). Then the tension of the thoracic aorta was recorded in presence of BRL37344 (BRL) to determine the action of β₃-AR. The tension of the thoracic aorta was also recorded in the presence of Propranolol (PRA), SR59230A (SR), L-NNA, H-89 and Iberiotoxin (IBTX) respectively to reveal the underling mechanism of β₃-AR activation on rat vascular smooth muscle. Immunohistochemistry was adopted to confirm the existence and the distribution of β₃-AR in rat thoracic aorta.. The results showed that: (1) The thoracic aorta was relaxed by β₃-AR activation, with a relaxation percentage of (10.59 ± 0.79). (2) β₃-AR was expressed in both endothelial and smooth muscle layer in thoracic aorta sections of rats. (3) PRA did not block the effect of BRL on the thoracic aorta. The relaxation actions of BRL could be antagonized by pre-incubating the thoracic aorta with SR. (4) L-NNA (a NOS inhibitor) and H-89 (a PKA inhibitor) reversed the relaxation effect of BRL on vascular smooth muscle. (5) The effect of BRL was decreased after application of Ibriotoxin (IBTX), a large conductance calcium dependent potassium channel blocker.. The results confirmed that activation of β₃-AR led to relaxation of thoracic aorta smooth muscle. The relaxation action of β₃-AR on smooth muscle of rat thoracic aorta was related to activation of NOS and PKA signaling pathway. Large conductance Ca²⁺-K⁺ channels were involved in the relaxation action of β₃-AR activation on rat thoracic aorta smooth muscle.

Topics: Animals; Aorta, Thoracic; In Vitro Techniques; Isoquinolines; Large-Conductance Calcium-Activated Potassium Channels; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroarginine; Peptides; Propanolamines; Propranolol; Rats; Receptors, Adrenergic, beta-3; Signal Transduction; Sulfonamides

The purpose of this study was to investigate the pre- and postsynaptic mechanisms that contribute to synaptic facilitation in the myenteric plexus of the trinitrobenzene sulphonic acid-inflamed guinea-pig distal colon. Intracellular recordings of evoked fast excitatory postsynaptic potentials (fEPSPs) in myenteric S neurons were evaluated, and the density of synaptic terminals was morphometrically analysed by transmission electron microscopy. In inflamed tissue, fEPSPs were reduced to control levels by the protein kinase A (PKA) inhibitor, H89, but H89 did not affect the fEPSPs in control tissue. This PKA activation in inflamed tissue did not appear to involve 5-HT(4) receptors because the antagonist/inverse agonist, GR 125487, caused comparable decreases of fEPSPs in both tissues. Inhibition of BK channels with iberiotoxin did not alter the fEPSPs in inflamed tissue, but increased the fEPSPs in control tissue to the amplitude detected in inflamed tissue. During trains of stimuli, run-down of EPSPs was less extensive in inflamed tissue and there was a significant increase in the paired pulse ratio. Depolarizations in response to exogenous neurotransmitters were not altered in inflamed tissue. These inflammation-induced changes were not accompanied by alterations in the pharmacological profile of EPSPs, and no changes in synaptic density were detected by electron microscopy. Collectively, these data indicate that synaptic facilitation in the inflamed myenteric plexus involves a presynaptic increase in PKA activity, possibly involving an inhibition of BK channels, and an increase in the readily releasable pool of synaptic vesicles.

Topics: Animals; Colitis; Colon; Cyclic AMP-Dependent Protein Kinases; Disease Models, Animal; Electric Stimulation; Enzyme Activation; Evoked Potentials; Excitatory Postsynaptic Potentials; Guinea Pigs; Isoquinolines; Large-Conductance Calcium-Activated Potassium Channels; Microscopy, Electron, Transmission; Myenteric Plexus; Neuronal Plasticity; Peptides; Potassium Channel Blockers; Presynaptic Terminals; Protein Kinase Inhibitors; Sulfonamides; Synaptic Transmission; Synaptic Vesicles; Time Factors; Trinitrobenzenesulfonic Acid

In artery smooth muscle, adenylyl cyclase-coupled receptors such as beta-adrenoceptors evoke Ca(2+) signals, which open Ca(2+)-activated potassium (BK(Ca)) channels in the plasma membrane. Thus, blood pressure may be lowered, in part, through vasodilation due to membrane hyperpolarization. The Ca(2+) signal is evoked via ryanodine receptors (RyRs) in sarcoplasmic reticulum proximal to the plasma membrane. We show here that cyclic adenosine diphosphate-ribose (cADPR), by activating RyRs, mediates, in part, hyperpolarization and vasodilation by beta-adrenoceptors. Thus, intracellular dialysis of cADPR increased the cytoplasmic Ca(2+) concentration proximal to the plasma membrane in isolated arterial smooth muscle cells and induced a concomitant membrane hyperpolarization. Smooth muscle hyperpolarization mediated by cADPR, by beta-adrenoceptors, and by cAMP, respectively, was abolished by chelating intracellular Ca(2+) and by blocking RyRs, cADPR, and BK(Ca) channels with ryanodine, 8-amino-cADPR, and iberiotoxin, respectively. The cAMP-dependent protein kinase A antagonist N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide hydrochloride (H89) blocked hyperpolarization by isoprenaline and cAMP, respectively, but not hyperpolarization by cADPR. Thus, cADPR acts as a downstream element in this signaling cascade. Importantly, antagonists of cADPR and BK(Ca) channels, respectively, inhibited beta-adrenoreceptor-induced artery dilation. We conclude, therefore, that relaxation of arterial smooth muscle by adenylyl cyclase-coupled receptors results, in part, from a cAMP-dependent and protein kinase A-dependent increase in cADPR synthesis, and subsequent activation of sarcoplasmic reticulum Ca(2+) release via RyRs, which leads to activation of BK(Ca) channels and membrane hyperpolarization.

Topics: Animals; Arteries; Calcium; Cell Membrane; Cells, Cultured; Cyclic ADP-Ribose; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dose-Response Relationship, Drug; Electrophysiology; Enzyme Inhibitors; Isoproterenol; Isoquinolines; Peptides; Potassium Channels; Rats; Ryanodine; Ryanodine Receptor Calcium Release Channel; Sarcoplasmic Reticulum; Sulfonamides; Time Factors; Vasodilator Agents

At birth, pulmonary vasodilation occurs as air-breathing life begins. The mechanism of O2-induced pulmonary vasodilation is unknown. We proposed that O2 causes fetal pulmonary vasodilation through activation of a calcium-dependent potassium channel (KCa) via a cyclic nucleotide-dependent kinase. We tested this hypothesis in hemodynamic studies in acutely prepared fetal lambs and in patch-clamp studies on resistance fetal pulmonary artery smooth muscle cells. Fetal O2 tension (PaO2) was increased by ventilating the ewe with 100% O2, causing fetal total pulmonary resistance to decrease from 1.18 +/- 0.14 to 0.41 +/- 0.03 mmHg per ml per min. Tetraethylammonium and iberiotoxin, preferential KCa-channel inhibitors, attenuated O2-induced fetal pulmonary vasodilation, while glibenclamide, an ATP-sensitive K+-channel antagonist, had no effect. Treatment with either a guanylate cyclase antagonist (LY83583) or cyclic nucleotide-dependent kinase inhibitors (H-89 and KT 5823) significantly attenuated O2-induced fetal pulmonary vasodilation. Under hypoxic conditions (PaO2 = 25 mmHg), whole-cell K+-channel currents (Ik) were small and were inhibited by 1 mM tetraethylammonium or 100 nM charybdotoxin (CTX; a specific KCa-channel blocker). Normoxia (PaO2 = 120 mmHg) increased Ik by more than 300%, and this was reversed by 100 nM CTX. Nitric oxide also increased Ik. Resting membrane potential was -37.2 +/- 1.9 mV and cells depolarized on exposure to CTX, while hyperpolarizing in normoxia. We conclude that O2 causes fetal pulmonary vasodilation by stimulating a cyclic nucleotide-dependent kinase, resulting in KCa-channel activation, membrane hyperpolarization, and vasodilation.

Topics: Alkaloids; Aminoquinolines; Animals; Carbazoles; Charybdotoxin; Endothelium, Vascular; Enzyme Inhibitors; Female; Fetus; Glyburide; Guanylate Cyclase; Hypoxia; Indoles; Isoquinolines; Membrane Potentials; Models, Cardiovascular; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Oxygen; Patch-Clamp Techniques; Peptides; Potassium Channel Blockers; Potassium Channels; Pregnancy; Protein Kinase Inhibitors; Pulmonary Artery; Sheep; Sulfonamides; Tetraethylammonium; Tetraethylammonium Compounds; Vasodilation