Endothelial coordination of cerebral vasomotion via myoendothelial gap junctions containing connexins 37 and 40

Control of cerebral vasculature differs from that of systemic vessels outside the blood-brain barrier. The hypothesis that the endothelium modulates vasomotion via direct myoendothelial coupling was investigated in a small vessel of the cerebral circulation. In the primary branch of the rat basilar artery, membrane potential, diameter, and calcium dynamics associated with vasomotion were examined using selective inhibitors of endothelial function in intact and endothelium-denuded arteries. Vessel anatomy, protein, and mRNA expression were studied using conventional electron microscopy high-resolution ultrastructural and confocal immunohistochemistry and quantitative PCR. Membrane potential oscillations were present in both endothelial cells and smooth muscle cells (SMCs), and these preceded rhythmical contractions during which adjacent SMC intracellular calcium concentration ([Ca2+]i) waves were synchronized. Endothelium removal abolished vasomotion and desynchronized adjacent smooth muscle cell [Ca2+]i waves. NG-nitro-l-arginine methyl ester (10 μM) did not mimic this effect, and dibutyryl cGMP (300 μM) failed to resynchronize [Ca2+]i waves in endothelium-denuded arteries. Combined charybdotoxin and apamin abolished vasomotion and depolarized and constricted vessels, even in absence of endothelium. Separately, 37,43Gap27 and 40Gap27 abolished vasomotion. Extensive myoendothelial gap junctions (3 per endothelial cell) composed of connexins 37 and 40 connected the endothelial cell and SMC layers. Synchronized vasomotion in rat basilar artery is endothelium dependent, with [Ca2+]i waves generated within SMCs being coordinated by electrical coupling via myoendothelial gap junctions.

Physiology and pharmacology of the oviducts of Raja and Scyliorhinus

1. In oviparous elasmobranchs the oviducts vary in structure and physiology according to how they carry the sperm upwards and the eggs down. The sperm are accompanied by a large volume of fluid secreted by the siphon. In some species this contains much 5-hydroxytryptamine (5HT), produced by a gland. The muscles of the oviducts are very sensitive to 5HT in Raja , which has such a gland, but not in Scyliorhinus , which has none. 2. The female Scyliorhinus draws the egg case down the duct by attaching tendrils to a rock or weeds and swimming round and round (Dodd 1983); the muscles of the lower oviduct and vagina are weak. 3. In Raja the egg case is buried in the sand or mud and there are powerful muscles in the lower oviduct and vagina. 4. In-vitro isolated strips of longitudinal or circular muscles of the lower oviduct of Raja give slow rhythmical contractions. 5-HT 10 -8 m increased the amplitude and frequency of contraction. The same response was induced by 8-OH-DPAT 5 x 10 -6 m (a 5-HT 1A receptor agonist) but not by 5 x 10 -6 m 2-methyl-5-HT (a 5-HT 3 agonist) or by 5 x 10 -6 m x-methyl-5-HT (a 5-HT 2 agonist). The response to 5-HT was partly blocked by methysergide 10 -6 m (a 5-HT 2 antagonist) but not by ketanserin 10 -5 m (a 5-HT 2 antagonist) or granisetron (BRL 43694) 10 -5 m (a5-HT 3 and 5-H T 4 antagonist). The receptor involved may therefore be of the 5-HT 1 or perhaps 5-HT 2 type. 5. Spontaneous contractions of the oviduct in Raja were inhibited by adrenalin 10 -6 m, and less strongly by noradrenaline 10 -6 m . 6. Substance P 10 -8 m produced increased amplitude and frequency of contraction. 7. Acetylcholine produced contraction only above a dose of 10 -6 m. 8. Strips of lower oviduct or vagina of Scyliorhinus canicula showed long periods of slight rhythmic activity punctuated by large rapid contractions at intervals of 10—40 min. 9. Similar large contractions occurred after addition of 5-HT at 10 -6 m but only in half the experiments and at high concentration, and with long delay. 10. Adrenalin produced large rapid contractions but only at a dose of 10 -7 M and above, and often after a long delay. 11. Substance P and acetylcholine also produced contraction, but the latter only at 10 -6 m . 12. Strips of the oviduct or vagina of either Raja or Scyliorhinus responded to a sudden stretch by a large contraction. 13. These findings are discussed in the light of the differences in sperm transport and egg laying in the two species.

Distension pressure on subserosal and mesenteric lymph pressures of rat jejunum

Lymph pressure (Pl) in the subserosal lymphatics and mesenteric lymphatics was determined in the jejunum at various intraluminal distension pressures (DP). Pl in the subserosal lymphatics was approximately equal to DP, in the range of 3–100 mmHg, whether the intestine was in the basal state or during water absorption. At a DP of 0 mmHg, Pl was 1.5 +/- 0.1 mmHg. When DP was 3, 10, 20, 40, 70, or 100 mmHg, Pl was 2.9 +/- 0.2, 11 +/- 1, 23 +/- 1, 43 +/- 1, 71 +/- 2, or 102 +/- 2 mmHg, respectively. From these findings and other considerations it is inferred that Pl in the subserosal lymphatics could be similar to the tissue fluid pressure, which is apparently determined by DP due to compression of the intestinal wall. On the other hand, Pl in the mesenteric lymphatics was not affected by DP at all. When DP was in the range of 0–70 mmHg with free flow of lymph, mean Pl was 6-8 mmHg, and it was 23–28 mmHg during lymphatic obstruction. During pressure measurement, rhythmical contractions of these lymphatics occurred, which may be mainly responsible for the increase of Pl and propulsion of lymph as well.

Lymph pressure in rat intestinal lymph duct with lymphatic obstruction

Lymph pressure (PL) in the main intestinal lymph duct with obstruction of lymph flow was determined. Under various conditions, the rate of lymph flow (JL) was essentially the same in either A rats (with communications between hepatic and intestinal lymphatics) or B rats (without such communications), but PL of A rats was significantly lower (P less than 0.01) than that of B rats. When the intestine was in the basal state, JL of A and B rats was 0.2-0.3 ml/h per rat, and PL was 1.5 +/- 0.2 and 3.3 +/- 0.2 mm/Hg, respectively. During fluid absorption, JL of A and B rats increased to 0.8-0.9 ml/h, and PL was 2.1 +/- 0.4 and 6.4 +/- 0.7 mmHg, respectively. During intravenous saline infusion, JL of A and B rats increased greatly to approximately 14 ml/h, and PL was 3.1 +/- 0.3 and 10.4 +/- 1.1 mmHg, respectively. The lower PL in A rats is apparently due to the possibility that during lymphatic obstruction most lymph could be drained off by the hepatic lymphatics. In A rats, luminal distension pressure had no effect on PL but in B rats PL decreased when distension pressure was 20 mmHg or higher. Furthermore, lymph pressure waves indicate the occurrence of rhythmical contractions of the lymph duct or its surrounding tissues, which may play a role in the propulsion of lymph.