Non-genomic mechanism of action of delta-4 and 5-reduced androgens and progestins on the contractility of the isolated rat myometrium

Effective concentrations50 of androgens, i.e. testosterone, androsterone, androstanediol, 5 beta-dihydrotestosterone and progestins: progesterone, pregnanolone, pregnanedione, epipregnanolone, allopregnanolone and allopregnanedione were assayed on the tonic contractions of the isolated rat myometrium induced by calcium in high-potassium calcium-free depolarizant solutions. Steroids showed their relaxant effect by fadding the sustained contraction induced by calcium in a depolarized state. Also, the addition of the calcium ionophores A-23187 and X-537A reversed the steroid relaxant effect by increasing sharply the tonic contraction. The possibility of steroid-induced relaxation through release of noradrenaline or histamine was discarded by blocking their specific receptors. From the results it is concluded that delta-4 and 5-reduced androgens and progestins produce relaxation by a myogenic mechanism acting on the smooth muscle cell, most likely by directly blocking the calcium channels they causing modulation of: the contraction-relaxation cycle.     

Physiological effects of androgens on human vascular endothelial and smooth muscle cells in culture

Androgenic hormones are associated with atherosclerotic cardiovascular disease, although the underlying cellular and molecular mechanisms remain unclear. This study examines the impact of androgens on the physiology of human vascular endothelial cells (EC) and smooth muscle cells (SMC) in culture. Cells were incubated with testosterone, dihydrotestosterone (DHT) or dehydroepiandrosterone (DHEA) at various physiological concentrations (5-50 nM) in the present or absence of an androgen receptor (AR) blocker flutamide (100 nM). Cell growth and death, DNA and collagen synthesis, and gene protein expression were assessed. It was shown that: (1) DHEA protected EC from superoxide injury via AR-independent mechanisms; (2) testosterone induced DNA synthesis and growth in EC via an AR-independent manner with activation of ERK1/2 activity; (3) DHT inhibited DNA synthesis and growth in EC in an AR-dependent manner; (4) testosterone and DHT enhanced ERK1/2 activation and proliferation in SMC via AR-independent and -dependent pathways, respectively; and (5) these androgens did not significantly affect collagen synthesis in SMC. We conclude that androgens possess multiple effects on vascular cells via either AR-dependent or -independent mechanisms. Testosterone and DHEA may be “beneficial” in preventing atherosclerosis by improving EC growth and survival; in contrast, stimulation of VSMC proliferation by testosterone and DHT is potentially “harmful”. The relationship of these in vitro effects by androgens to in vivo vascular function and atherogenesis needs to be further clarified.     

The action of PKA on smooth muscle myosin phosphorylation

The aim of the study is to reveal the characterization of PKA acting on myosin. We found: (a) in the absence of Ca(2+)/CaM, PKA slightly phosphorylated MLC(20) and stimulated the Mg(2+)-ATPase activity of myosin, which was strengthened significantly by arachidonic acid (ACAD); (b) Ca(2+)-independent phosphorylation of myosin by PKA was obviously less efficient than both Ca(2+)-dependent and independent phosphorylation of myosin by MLCK; (c) micro-amount of calponin could not increase the precipitation of myosin phosphorylated by PKA, but it increased the precipitation of myosin phosphorylated by MLCK, suggesting the presence of conformational differences between the myosins phosphorylated by PKA and by MLCK.     

Mechanisms of action of pH-induced effects on vascular smooth muscle

It is clear that pH has many effects on vascular smooth muscle and the overall action of pH on force will depend on the type of vascular smooth muscle in question and the combined effects on all the potential modulatory mechanisms. The major effects of pH on force appear to be mediated via modulation of [Ca]_i rather than changes in the sensitivity of the contractile machinery to Ca²⁺. There are still numerous gaps in our understanding of the actions of pH and as more data become available, we will be able to better understand the major mechanisms involved. (Mol Cell Biochem 263: 163–172, 2004)     

Mechanisms of action of pH-induced effects on vascular smooth muscle

It is clear that pH has many effects on vascular smooth muscle and the overall action of pH on force will depend on the type of vascular smooth muscle in question and the combined effects on all the potential modulatory mechanisms. The major effects of pH on force appear to be mediated via modulation of [Ca]i rather than changes in the sensitivity of the contractile machinery to Ca2+. There are still numerous gaps in our understanding of the actions of pH and as more data become available, we will be able to better understand the major mechanisms involved.     

The contractile action of platelet-activating factor on gallbladder smooth muscle

Platelet-activating factor (PAF) may be a mediator of some sequelae of cholecystitis, a disorder with gallbladder motor dysfunction. The aims of this study were to determine the effect and mechanism of PAF on gallbladder muscle. Exogenous administration of PAF-16 or PAF-18 caused dose-dependent contractions of gallbladder muscle strips in vitro with threshold doses of 1 ng/ml and 10 ng/ml, respectively. The PAF-induced contractions were not significantly reduced by TTX, atropine, or hexamethonium but were significantly inhibited with the PAF receptor antagonists ginkolide B and CV-3988. The PAF-induced contraction was reduced by indomethacin. Preventing influx of extracellular calcium with a calcium-free solution nearly abolished the PAF contractile response. Nifedipine inhibited the PAF contractile response, whereas ryanodine had no effect. Pertussis toxin reduced the PAF contractile response. In conclusion, PAF causes gallbladder contraction through specific PAF receptors on gallbladder muscle. These PAF receptors appear to be linked to a prostaglandin-mediated mechanism and to pertussis toxin-sensitive G proteins. The contractile response is largely mediated through the utilization of extracellular calcium influx through voltage-dependent calcium channels.     

Relaxing action of a holothurian toxin on mammalian smooth muscle

1. The crude epidermal mucous secretion produced by the sea cucumber Holothuria mexicana Ludwig inhibits the tonus and spontaneous mechanical activity of rabbit ileum at concentrations of 0.1 mg/ml and higher. 2. This effect, similar to that of epinephrine, is attributed to a compound referred to as mucotoxin (MuTX). 3. MuTX also relaxes strips of the rabbit aorta contracted by 10(-8) M norepinephrine and exerts a similar, less marked, effect on the same strips contracted in high potassium solutions. 4. These observations suggest that the relaxing effect of MuTX on mammalian smooth muscle is not mediated by an adrenergic mechanism.     

Propagated repolarization of simulated action potentials in cardiac muscle and smooth muscle

Background  

Propagation of repolarization is a phenomenon that occurs in cardiac muscle. We wanted to test whether this phenomenon would also occur in our model of simulated action potentials (APs) of cardiac muscle (CM) and smooth muscle (SM) generated with the PSpice program.     

The insect neuropeptide proctolin can affect the CNS and the smooth=muscle of mammals

The insect neurotransmitter proctolin can affect different behavioural parameters in rats after intracerebroventricular administration. Proctolin decreased the horizontal exploratory activity and induced a long-lasting analgesia in a hot-plate test. Proctolin lenghthened the passive avoidance latency of rats after post-trial treatment and also in the pre-retention test situation. The self-stimulation rate of rats was significantly diminished after i.c.v. proctolin administration. Proctolin also induced in rat and mouse ileum in vitro a dose-dependent contraction of the gut smooth-muscle that can be blocked by atropine. The results show that an invertebrate neuropeptide (or its fragments) can also be active in mammals. The physiological relevance of the effects observed recently is unknown.     

Antiapoptotic action of carbon monoxide on cultured vascular smooth muscle cells

Vascular smooth muscle cells (SMCs) generate carbon monoxide (CO) from the degradation of heme by the enzyme heme oxygenase. Because recent studies indicate that CO influences the properties of vascular SMCs, we examined whether this diatomic gas regulates apoptosis in vascular SMCs. Treatment of cultured rat aortic SMCs with a cytokine cocktail consisting of interleukin-1beta (5 ng/ml), tumor necrosis factor-alpha (20 ng/ml), and interferon-gamma (200 U/ml) for 48 hr stimulated apoptosis, as demonstrated by DNA laddering, caspase-3 activation, and annexin V staining. However, the exogenous addition of CO (200 ppm) completely blocked cytokine-mediated apoptosis. The antiapoptotic action of CO was partially reversed by the soluble guanylate cyclase inhibitor, H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 microM). In contrast, the p38 mitogen-activated protein kinase inhibitor, SB203580 (10 microM), had no effect on SMC apoptosis. These findings indicate that CO is a potent inhibitor of vascular SMC apoptosis and that it blocks apoptosis, in part, by activating the cGMP signaling pathway. The ability of CO to inhibit vascular SMC apoptosis may play a critical role in attenuating lesion formation at sites of arterial damage.     

Endothelin action on vascular smooth muscle involves inositol trisphosphate and calcium mobilization

Cultured endothelial cells release a potent vasoconstrictor peptide, endothelin. Cumulative addition of synthetic endothelin to isolated rabbit aortic rings elicited a concentration-dependent increase in contractile tension which was endothelium-independent. In cultured rabbit vascular smooth muscle cells loaded with the fluorescent dye fura 2, endothelin induced a concentration-dependent increase in [Ca2+]i over the range of 0.01 to 100 nM. Moreover, in the absence of extracellular Ca2+, endothelin could still induce an increase in [Ca2+]i. In addition, endothelin stimulated 45Ca2+ efflux from preloaded vascular smooth muscle cells in the presence and absence of extracellular Ca2+, as well as stimulating 45Ca2+ influx in a concentration-dependent manner. Measurement of inositol phosphates in [3H]-myoinositol-labelled vascular vascular trisphosphate. Unlabelled endothelin inhibited (125I)-endothelin binding to cultured rabbit vascular smooth muscle cells in a concentration-dependent manner. Binding was not inhibited by other vasoactive hormones or calcium channel ligands, suggesting cell surface receptors specific for endothelin. We conclude that one of the initial membrane events in the action of endothelin is to induce phospholipase C-stimulated PIP2 hydrolysis and that this signalling mechanism is initiated by endothelin/receptor interaction at the plasma membrane.     

Control of urinary bladder smooth muscle excitability by the TRPM4 channel modulator 9-phenanthrol

The Ca²⁺-activated monovalent cation selective transient receptor potential melastatin 4 (TRPM4) channel has been recently identified in detrusor smooth muscle (DSM) of the urinary bladder. Two recent publications by our research group provide evidence in support of the novel hypothesis that TRPM4 channels enhance DSM excitability and contractility. This is a critical question as prior studies have primarily targeted hyperpolarizing currents facilitated by K⁺ channels, but the depolarizing component in DSM cells is not well understood. For the first time, we utilized the selective TRPM4 channel inhibitor, 9-phenanthrol, to investigate TRPM4 channel functional effects in DSM at both cellular and tissue levels in rodents. Our new data presented here showed that in rat DSM cells, 9-phenanthrol attenuates spontaneous inward currents in the presence of the muscarinic receptor agonist, carbachol, thus reducing DSM cell excitability. In support of our original hypothesis, we found that TRPM4 channel mRNA levels are much higher in DSM vs. vascular smooth muscle and that inhibition of TRPM4 channels can potentially attenuate DSM excitability. Thus, we postulate the novel concept that selective pharmacological inhibition of TRPM4 channels can limit both excitability and contractility of DSM.