Calcium and electrical dynamics in lymphatic endothelium.

KEY POINTS: Endothelial cell function in resistance arteries integrates Ca2+ signalling with hyperpolarization to promote relaxation of smooth muscle cells and increase tissue blood flow. Whether complementary signalling occurs in lymphatic endothelium is unknown. Intracellular calcium and membrane potential were evaluated in endothelial cell tubes freshly isolated from mouse collecting lymphatic vessels of the popliteal fossa. Resting membrane potential measured using intracellular microelectrodes averaged ∼-70 mV. Stimulation of lymphatic endothelium by acetylcholine or a TRPV4 channel agonist increased intracellular Ca2+ with robust depolarization. Findings from Trpv4-/- mice and with computational modelling suggest that the initial mobilization of intracellular Ca2+ leads to influx of Ca2+ and Na+ through TRPV4 channels to evoke depolarization. Lymphatic endothelial cells lack the Ca2+ -activated K+ channels present in arterial endothelium to generate endothelium-derived hyperpolarization. Absence of this signalling pathway with effective depolarization may promote rapid conduction of contraction along lymphatic muscle during lymph propulsion. ABSTRACT: Subsequent to a rise in intracellular Ca2+ ([Ca2+ ]i ), hyperpolarization of the endothelium coordinates vascular smooth muscle relaxation along resistance arteries during blood flow control. In the lymphatic vasculature, collecting vessels generate rapid contractions coordinated along lymphangions to propel lymph, but the underlying signalling pathways are unknown. We tested the hypothesis that lymphatic endothelial cells (LECs) exhibit Ca2+ and electrical signalling properties that facilitate lymph propulsion. To study electrical and intracellular Ca2+ signalling dynamics in lymphatic endothelium, we excised collecting lymphatic vessels from the popliteal fossa of mice and removed their muscle cells to isolate intact LEC tubes (LECTs). Intracellular recording revealed a resting membrane potential of ∼-70 mV. Acetylcholine (ACh) increased [Ca2+ ]i with a time course similar to that observed in endothelium of resistance arteries (i.e. rapid initial peak with a sustained 'plateau'). In striking contrast to the endothelium-derived hyperpolarization (EDH) characteristic of arteries, LECs depolarized (>15 mV) to either ACh or TRPV4 channel activation. This depolarization was facilitated by the absence of Ca2+ -activated K+ (KCa ) channels as confirmed with PCR, persisted in the absence of extracellular Ca2+ , was abolished by LaCl3 and was attenuated ∼70% in LECTs from Trpv4-/- mice. Computational modelling of ion fluxes in LECs indicated that omitting K+ channels supports our experimental results. These findings reveal novel signalling events in LECs, which are devoid of the KCa activity abundant in arterial endothelium. Absence of EDH with effective depolarization of LECs may promote the rapid conduction of contraction waves along lymphatic muscle during lymph propulsion.

Maternal fructose-intake-induced renal programming in adult male offspring.

Nutrition in pregnancy can elicit long-term effects on the health of offspring. Although fructose consumption has increased globally and is linked to metabolic syndrome, little is known about the long-term effects of maternal high-fructose (HF) exposure during gestation and lactation, especially on renal programming. We examined potential key genes and pathways that are associated with HF-induced renal programming using whole-genome RNA next-generation sequencing (NGS) to quantify the abundance of RNA transcripts in kidneys from 1-day-, 3-week-, and 3-month-old male offspring. Pregnant Sprague-Dawley rats received regular chow or chow supplemented with HF (60% diet by weight) during the entire period of pregnancy and lactation. Male offspring exhibited programmed hypertension at 3 months of age. Maternal HF intake modified over 200 renal transcripts from nephrogenesis stage to adulthood. We observed that 20 differentially expressed genes identified in 1-day-old kidney are related to regulation of blood pressure. Among them, Hmox1, Bdkrb2, Adra2b, Ptgs2, Col1a2 and Tbxa2r are associated with endothelium-derived hyperpolarizing factor (EDHF). NGS also identified genes in arachidonic acid metabolism (Cyp2c23, Hpgds, Ptgds and Ptges) that may be potential key genes/pathways contributing to renal programming and hypertension. Collectively, our NGS data suggest that maternal HF intake elicits a defective adaptation of interrelated EDHFs during nephrogenesis which may lead to renal programming and hypertension in later life. Moreover, our results highlight genes and pathways involved in renal programming as potential targets for therapeutic approaches to prevent metabolic-syndrome-related comorbidities in children with HF exposure in early life.

Influence of Sex on Gap Junctional Distribution and Vascular Dilatation in the Rat Mesenteric Arteries / 대한마취과학회지

BACKGROUND: Besides prostacyclin and nitric oxide, the endothelium-derived hyperpolarizing factor (EDHF), which is another distinct endothelium-dependent vasodilator, is involved in relaxing the vascular smooth muscle cells. The myoendothelial gap junction (MEGJ) and female sex hormone play important roles in the EDHF-mediated responses. Therefore, this study was designed to determine the influence of gender on the gap junctional distribution and endothelium-dependent vasodilation in the rat mesenteric arteries. METHODS: Male and female Sprague-Dawley rat were euthanized and the tertiary branch of the mesenteric artery was harvested. Immunohistochemistry and confocal microscopic examination of the arterial wall were performed after treating them with specific antibodies to delineate the distribution of connexin 43, a gap junctional protein. Segments of the mesenteric artery, 5 mm in length, were connected to two tungsten wires under isometric tension. The arterial segments were suspended in a modified Krebs solution (37 degrees C) aerated with 95% O2 and 5% CO2 in a vertical water-jacketed temperature-controlled tissue bath. The standard dose-response curve for acetylcholine (10(-9)-10(-5) M) was drawn in the presence of the NO synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME; 10(-4) M) plus indomethacin (10(-5) M) and/or gap junctional inhibitor, carbenoxolone (10(-4) M). RESULTS: In the female rat mesenteric artery, the gap junctional plagues were more prevalent particularly along the endothelial layer. The inhibition of the relaxation response to acetylcholine was depressed in the presence of L-NAME plus indomethacin and augmented in the presence of carbenoxolone when compared with the male rat mesenteric arteries (P < 0.05). CONCLUSIONS: Gender differences in the rat mensenteric arteries have an effect on the expression of connexin 43 and the release of EDHF through MEGJ may play a key role in controlling the female arterial tone.

Influence of Myoendothelial Gap Junction on the Regulation of Vasomotor Tone / 대한마취과학회지

BACKGROUND: In addition to nitric oxide (NO) and prostacyclin (PGI2), there is another endothelium-derived mechanism of smooth muscle relaxation, which is associated with an endothelium-derived hyperpolarizing factor (EDHF). To assess the role of gap junctions in endothelium dependent hyperpolarization, we investigated the relationship between distribution of myoendothelial gap junction (MEGJ) and relative importance of the EDHF pathway in the regulation of vascular tone. METHODS: Immunohistochemistry and confocal microscopic examination of the mesenteric arterial wall of male Sprague-Dawley rat following treatment with specific antibodies were performed to delineate the distribution of connexin 43, a gap junctional protein. The standard dose-response curve for acetylcholine (10-9-10-5 M) of the mesenteric artery was regarded as the release of EDHF in the presence of the NO synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME, 10-4 M) and indomethacine (10-5 M). The effects of the gap junction inhibitors such as 18alpha-glycyrrhetinic acid (18alpha-GA; (2 x 10-4 M)) and carbenoxolone (3 x 10-4 M) was assessed regarding relaxtion to acetylcholine, contraction to phenylephrine (5 x 10-6 M) in the proximal and distal mesenteric arteries. RESULTS: In the distal artery, gap junctional plaques were more prevalent, and the relaxation response to acetylcholine was augmented and the contraction response to phenylephrine was depressed compared with the proximal artery. In both the proximal and distal mesenteric arteries, acetylcholine-induced relaxations attributable to EDHF were near completely blocked by 18alpha-GA and carbenoxolone to the same degree. Regardless of the presence of L-NAME plus indomethacin, 18alpha-GA significantly augmented the contraction response to phenylephrine. CONCLUSIONS: The vasomotor regulatory response by EDHF in the rat mesenteric arteries may be explained by extensive heterocellular coupling through MEGJs. Moreover, the release of EDHF through MEGJ may have a essential role in the regulation of resistor arterial tone.

The endothelium in health and disease: A discussion of the contribution of non-nitric oxide endothelium-derived vasoactive mediators to vascular homeostasis in normal vessels and in type II diabetes.

Endothelial dysfunction is considered as a major risk factor of cardiovascular complications of type I and types II diabetes. Impaired endothelium-dependent vasodilatation can be directly linked to a decreased synthesis of the endothelium-derived nitric oxide (NO) and/or an increase in the production of reactive oxygen species such as superoxide. Administration of tetrahydrobiopterin, an important co-factor for the enzyme nitric oxide synthase (NOS), has been demonstrated to enhance NO production in prehypertensive rats, restore endothelium-dependent vasodilatation in coronary arteries following reperfusion injury, aortae from streptozotocin-induced diabetic rats and in patients with hypercholesterolemia. Tetrahydrobiopterin supplementation has been shown to improve endothelium-dependent relaxation in normal individuals, patients with type II diabetes and in smokers. These findings from different animal models as well as in clinical trials lead to the hypothesis that tetrahydrobiopterin, or a precursor thereof, could be a new and an effective therapeutic approach for the improvement of endothelium function in pathophysiological conditions. In addition to NO, the endothelium also produces a variety of other vasoactive factors and a key question is: Is there also a link to changes in the synthesis/action of these other endothelium-derived factors to the cardiovascular complications associated with diabetes? Endothelium-derived hyperpolarizing factor, or EDHF, is thought to be an extremely important vasodilator substance notably in the resistance vasculature. Unfortunately, the nature and, indeed, the very existence of EDHF remains obscure. Potentially there are multiple EDHFs demonstrating vessel selectivity in their actions. However, until now, identity and properties of EDHF that determine the therapeutic potential of manipulating EDHF remains unknown. Here we briefly review the current status of EDHF and the link between EDHF and endothelial dysfunction associated with diabetes. (Mol Cell Biochem 263: 21-27, 2004).