Regulation of pulmonary venous tone in response to muscarinic receptor activation

Vascular Reactions of the Diving Reflex in Men and Women Carrying Different ADRA1A Genotypes

The diving reflex is an oxygen-saving mechanism which is accompanied by apnea, reflex bradycardia development, peripheral vasoconstriction, spleen erythrocyte release, and selective redistribution of blood flow to the organs most vulnerable to lack of oxygen, such as the brain, heart, and lungs. However, this is a poorly studied form of hypoxia, with a knowledge gap on physiological and biochemical adaptation mechanisms. The reflective sympathetic constriction of the resistive vessels is realized via ADRA1A. It has been shown that ADRA1A SNP (p.Arg347Cys; rs1048101) is associated with changes in tonus in vessel walls. Moreover, the Cys347 allele has been shown to regulate systolic blood pressure. The aim of this work was to evaluate whether the ADRA1A polymorphism affected the pulmonary vascular reactions in men and women in response to the diving reflex. Men (n = 52) and women (n = 50) untrained in diving aged 18 to 25 were recruited into the study. The vascular reactions and blood flow were examined by integrated rheography and rheography of the pulmonary artery. Peripheral blood circulation was registered by plethysmography. The ADRA1A gene polymorphism (p.Arg347Cys; rs1048101) was determined by PCR-RFLP. In both men and women, reflective pulmonary vasodilation did occur in response to the diving reflex, but in women this vasodilation was more pronounced and was accompanied by a higher filling of the lungs with blood.. Additionally, ADRA1A SNP (p.Arg347Cys; rs1048101) is associated with sex. Interestingly, women with the Arg347 allele demonstrated the highest vasodilation of the lung vessels. Therefore, our data may help to indicate women with the most prominent adaptive reactions to the diving reflex. Our data also indicate that women and men with the Cys allele of the ADRA1A gene polymorphism have the highest risk of developing lung hypertension in response to the diving reflex. The diving reflex is an oxygen-saving mechanism which is accompanied by apnea, reflex bradycardia development, peripheral vasoconstriction, spleen erythrocyte release, and selective redistribution of blood flow to the organs most vulnerable to lack of oxygen, such as the brain, heart, and lungs. However, this is a poorly studied form of hypoxia, with a knowledge gap on physiological and biochemical adaptation mechanisms.

Pulmonary Microcirculation during Experimental Pulmonary Thromboembolism under Conditions of Activation and Blockade of Muscarinic Acetylcholine Receptors

Changes in pulmonary microcirculation were studied in isolated perfused rabbit lungs during modelling pulmonary thromboembolism under conditions of acetylcholine infusion against the background of treatment with M1 acetylcholine receptor blocker pirenzepine or blockade of muscarinic acetylcholine receptors with atropine. In the first case, the increase in pulmonary artery pressure was less pronounced than in case of atropine treatment. In response to pulmonary embolism after acetylcholine infusion against the background of pirenzepine pretreatment, the capillary hydrostatic pressure and postcapillary resistance did not change, while after atropine treatment, these parameters increased. In case of pulmonary embolism after acetylcholine infusion combined with selective blockade of M1 muscarinic acetylcholine receptors, the capillary filtration coefficient increased to a greater extent, than in the control and after blockade of muscarinic acetylcholine receptors.

Roles of ion channels in regulation of acetylcholine-mediated vasoconstrictions in umbilical cords of rabbit/rats

We recently demonstrated that acetylcholine (ACh) produced reliable vasoconstrictions in the umbilical cords. This study investigated the possible mechanisms with different antagonists. ACh-mediated vasoconstrictions were decreased by voltage-operated calcium (Ca²⁺) channels antagonist nifedipine or inositol-1,4,5-trisphosphate-mediated Ca²⁺ release antagonist 2-aminoethyl diphenylborinate, indicating that both extracellular and intracellular calcium modulated the ACh-stimulated umbilical contraction. Intracellular Ca²⁺ concentrations were increased simultaneously with vasoconstrictions by ACh in the umbilical vessels. Inhibiting large-conductance calcium-dependent potassium (BK) channels enhanced ACh-mediated contraction, whereas inhibiting voltage dependent potassium (K⁺), inward rectifier K⁺ and ATP-sensitive K⁺ channels had no effects. Incubation with specific K⁺ channel inhibitors showed that ACh suppressed BK currents rather than 4-aminopyridine-sensitive K⁺ channels currents. The results suggested that blood vessels in umbilical cords had special characteristics in response to cholinergic signals. ACh-stimulated umbilical vasoconstrictions were mediated via muscarinic receptor subtype 1/3-protein kinase C/cyclooxygenase-BK channel pathways.

Hypoxia sensitivity of a voltage-gated potassium current in porcine intrapulmonary vein smooth muscle cells

Hypoxia contracts the pulmonary vein, but the underlying cellular effectors remain unclear. Utilizing contractile studies and whole cell patch-clamp electrophysiology, we report for the first time a hypoxia-sensitive K(+) current in porcine pulmonary vein smooth muscle cells (PVSMC). Hypoxia induced a transient contractile response that was 56 ± 7% of the control response (80 mM KCl). This contraction required extracellular Ca(2+) and was sensitive to Ca(2+) channel blockade. Blockade of K(+) channels by tetraethylammonium chloride (TEA) or 4-aminopyridine (4-AP) reversibly inhibited the hypoxia-mediated contraction. Single-isolated PVSMC (typically 159.1 ± 2.3 μm long) had mean resting membrane potentials (RMP) of -36 ± 4 mV with a mean membrane capacitance of 108 ± 3.5 pF. Whole cell patch-clamp recordings identified a rapidly activating, partially inactivating K(+) current (I(KH)) that was hypoxia, TEA, and 4-AP sensitive. I(KH) was insensitive to Penitrem A or glyburide in PVSMC and had a time to peak of 14.4 ± 3.3 ms and recovered in 67 ms following inactivation at +80 mV. Peak window current was -32 mV, suggesting that I(KH) may contribute to PVSMC RMP. The molecular identity of the potassium channel is not clear. However, RT-PCR, using porcine pulmonary artery and vein samples, identified Kv(1.5), Kv(2.1), and BK, with all three being more abundant in the PV. Both artery and vein expressed STREX, a highly conserved and hypoxia-sensitive BK channel variant. Taken together, our data support the hypothesis that hypoxic inhibition of I(KH) would contribute to hypoxic-induced contraction in PVSMC.

Muscarinic receptor M1 and phosphodiesterase 1 are key determinants in pulmonary vascular dysfunction following perinatal hypoxia in mice

Perinatal adverse events such as limitation of nutrients or oxygen supply are associated with the occurrence of diseases in adulthood, like cardiovascular diseases and diabetes. We investigated the long-term effects of perinatal hypoxia on the lung circulation, with particular attention to the nitric oxide (NO)/cGMP pathway. Mice were placed under hypoxia in utero 5 days before delivery and for 5 days after birth. Pups were then bred in normoxia until adulthood. Adults born in hypoxia displayed an altered regulation of pulmonary vascular tone with higher right ventricular pressure in normoxia and increased sensitivity to acute hypoxia compared with controls. Perinatal hypoxia dramatically decreased endothelium-dependent relaxation induced by ACh in adult pulmonary arteries (PAs) but did not influence NO-mediated endothelium-independent relaxation. The M(3) muscarinic receptor was implicated in the relaxing action of ACh and M(1) muscarinic receptor (M(1)AChR) in its vasoconstrictive effects. Pirenzepine or telenzepine, two preferential inhibitors of M(1)AChR, abolished the adverse effects of perinatal hypoxia on ACh-induced relaxation. M(1)AChR mRNA expression was increased in lungs and PAs of mice born in hypoxia. The phosphodiesterase 1 (PDE1) inhibitor vinpocetine also reversed the decrease in ACh-induced relaxation following perinatal hypoxia, suggesting that M(1)AChR-mediated alteration of ACh-induced relaxation is due to the activation of calcium-dependent PDE1. Therefore, perinatal hypoxia leads to an altered pulmonary circulation in adulthood with vascular dysfunction characterized by impaired endothelium-dependent relaxation and M(1)AChR plays a predominant role. This raises the possibility that muscarinic receptors could be key determinants in pulmonary vascular diseases in relation to "perinatal imprinting."

Differential effects of intravenous anesthetics on capacitative calcium entry in human pulmonary artery smooth muscle cells

We assessed the roles of the protein kinase C (PKC) and the tyrosine kinase (TK) signaling pathways in regulating capacitative calcium entry (CCE) in human pulmonary artery smooth muscle cells (PASMCs) and investigated the effects of intravenous anesthetics (midazolam, propofol, thiopental, ketamine, etomidate, morphine, and fentanyl) on CCE in human PASMCs. Fura-2-loaded human PASMCs were placed in a dish (37°C) on an inverted fluorescence microscope. Intracellular Ca2+concentration ([Ca2+]i) was measured as the 340/380 fluorescence ratio in individual PASMCs. Thapsigargin, a sarcoplasmic reticulum Ca2+-adenosine triphosphatase inhibitor, was used to deplete intracellular Ca2+stores after removing extracellular Ca2+. CCE was then activated by restoring extracellular Ca2+(2.2 mM). The effects of PKC activation and inhibition, TK inhibition, and the intravenous anesthetics on CCE were assessed. Thapsigargin caused a transient increase in [Ca2+]i. Restoring extracellular Ca2+caused a rapid peak increase in [Ca2+]i, followed by a sustained increase in [Ca2+]i; i.e., CCE was stimulated in human PASMCs. PKC activation attenuated ( P < 0.05), whereas PKC inhibition potentiated ( P < 0.05), both peak and sustained CCE. TK inhibition attenuated ( P < 0.05) both peak and sustained CCE. Midazolam, propofol, and thiopental each attenuated ( P < 0.05) both peak and sustained CCE, whereas ketamine, etomidate, morphine, and fentanyl had no effect on CCE. Our results suggest that CCE in human PASMCs is influenced by both the TK and PKC signaling pathways. Midazolam, propofol, and thiopental each attenuated CCE, whereas ketamine, etomidate, morphine, and fentanyl had no effect on CCE.

The differential effects of intravenous anesthetics on myofilament Ca2+ sensitivity in pulmonary venous smooth muscle

BACKGROUND

Pulmonary venous contraction can increase pulmonary capillary pressure and pulmonary edema. In the present study, we investigated the direct effects of ketamine, etomidate, thiopental, and midazolam on pulmonary venous contraction and myofilament Ca2+ sensitivity in permeabilized pulmonary venous smooth muscle (PVSM).

METHODS

The effects of these IV anesthetics on acetylcholine contraction were assessed in isolated canine pulmonary vein rings. Tension and [Ca2+]i were measured simultaneously in fura-2 loaded endothelium-denuded PVSM strips after being permeabilized with alpha-toxin. The effects of the IV anesthetics on tension ([Ca2+]i remains constant) in the absence or the presence of muscarinic receptor activation (acetylcholine) were assessed. The immunofluorescence technique and confocal microscopy were used to localize the cellular distribution of protein kinase C (PKC) isoforms in PVSM cells before and after the addition of ketamine.

RESULTS

Ketamine, etomidate, and midazolam each attenuated acetylcholine contraction dose-dependently, whereas thiopental had no effect. None of the IV anesthetics alone had an effect on tension in strips at constant [Ca2+]i (i.e., they had no direct effect on myofilament Ca2+ sensitivity). Acetylcholine increased tension by 56% +/- 7% at constant [Ca2+]i. In acetylcholine-stimulated strips, etomidate, midazolam, and thiopental had no additional effect on tension at constant [Ca2+]i, whereas ketamine decreased tension by 33% +/- 3%. Activation with acetylcholine induced translocation of PKC from cytoplasm to membrane, and this effect was blocked by ketamine.

CONCLUSIONS

Ketamine, etomidate, and midazolam each attenuated acetylcholine-induced pulmonary venous contraction. Ketamine attenuates acetylcholine contraction by inhibiting the acetylcholine-induced increase in myofilament Ca2+ sensitivity and the acetylcholine-induced translocation of PKCalpha.

Adrenoceptor and cholinoceptor modulation of rat pulmonary vein cardiac muscle contractility

Cardiac muscle extends into mammalian pulmonary veins for variable distances according to species. This study has addressed the autonomic control of electrically paced cardiac muscle of the pulmonary vein of the rat. Contractile responses of Wistar rat pulmonary veins were investigated under isometric conditions in vitro. Vessels were electrically paced at 1 Hz (10 V, 1 ms pulse width). Acetylcholine (ACh, 1 nM-10 microM) attenuated the contractile response (maximum inhibition at 1 microM, 41+/-15%, mean+/-SD). The attenuation was inhibited by atropine (p<0.05) and partially inhibited (7+/-4%, mean+/-SD, p<0.01) by removal of the endothelium. Noradrenaline (NA, 1 nM-10 microM) augmented the cardiac muscle contractility in a fashion partially inhibited by atenolol; augmentation at 10 microM was reduced from 169+/-9% (n=6) to 135+/-9% (n=5), (p<0.05). The ability of ACh to attenuate the contractile responses was unaffected by the presence of NA. In conclusion, ACh has a muscarinic receptor-mediated negative inotropic effect upon the cardiac muscle of the pulmonary vein of the rat mediated in part by the endothelium. The cardiac muscle expresses a positive inotropic response to NA partly mediated by beta1-adrenoceptors that can be antagonised by ACh. Therefore, pulmonary vein cardiac muscle function is modulated by competing autonomic influences which may be of significance to the generation of atrial fibrillation events.

Cellular mechanisms of thromboxane A2-mediated contraction in pulmonary veins

Our objectives were to identify the relative contributions of [Ca2+]i and myofilament Ca2+ sensitivity in the pulmonary venous smooth muscle (PVSM) contractile response to the thromboxane A2 mimetic U-46619 and to assess the roles of PKC, tyrosine kinases (TK), and Rho-kinase (ROK) in that response. We tested the hypothesis that U-46619-induced contraction in PVSM is mediated by both increases in [Ca2+]i and myofilament Ca2+ sensitivity and that the PKC, TK, and ROK signaling pathways are involved. Isometric tension was measured in isolated endothelium-denuded (E-) canine pulmonary venous (PV) rings. In addition, [Ca2+]i and tension were simultaneously measured in fura-2-loaded E- PVSM strips. U-46619 (0.1 nM-1 microM) caused dose-dependent (P < 0.001) contraction in PV rings. U-46619 contraction was attenuated by inhibitors of L-type voltage-operated Ca2+ channels (nifedipine, P < 0.001), inositol 1,4,5-trisphosphate-mediated Ca2+ release (2-aminoethoxydiphenylborate, P < 0.001), PKC (bisindolylmaleimide I, P < 0.001), TK (tyrphostin A-47, P = 0.014), and ROK (Y-27632, P = 0.008). In PV strips, U-46619 contraction was associated with increases in [Ca2+]i and myofilament Ca2+ sensitivity. Both Ca2+ influx and release mediated the early transient increase in [Ca2+]i, whereas the late sustained increase in [Ca2+]i only involved Ca2+ influx. Inhibition of both PKC and ROK (P = 0.006 and P = 0.002, respectively), but not TK, attenuated the U-46619-induced increase in myofilament Ca2+ sensitivity. These results suggest that U-46619 contraction is mediated by Ca2+ influx, Ca2+ release, and increased myofilament Ca2+ sensitivity. The PKC, TK, and ROK signaling pathways are involved in U-46619 contraction.