Intercellular ultrafast Ca(2+) wave in vascular smooth muscle cells: numerical and experimental study

Calcium response of spatially arranged cell networks to shear stress by confined single cell patterned microfluidic chips

Osteoblasts in multicellular organisms are sensitive to fluid shear stress (Fss) and respond smartly with versatile patterns of intracellular calcium signal ([Ca²⁺]_i). In this study, a spatial-single cell patterning method was developed by combining micro-contact printing (μCP) and reversible microfluidic chip mounted with vacuum together. Based on this well-defined patterning platform, it's possible to investigate calcium response to Fss modulated by spatial factors, and to characterize multiple calcium patterns quantitatively in terms of cell spacing and cell orientation. The result showed that the Fss-induced [Ca²⁺]_i profiles revealed oscillational signal patterns in non-connected cells such as those in physical-contacted cells. Close-arrayed osteoblasts showed remarkably more [Ca²⁺]_i oscillations than sparse-arrayed cells. The circular shape of the cells was sensitive to oscillational [Ca²⁺]_i as a potential major cause. The consistency of cell orientation and shear stress promoted temporal homogeneity of calcium oscillations.

Shifting into high gear: how interstitial cells of Cajal change the motility pattern of the developing intestine

The first contractile waves in the developing embryonic gut are purely myogenic; they only involve smooth muscle. Here, we provide evidence for a transition from smooth muscle to interstitial cell of Cajal (ICC)-driven contractile waves in the developing chicken gut. In situ hybridization staining for anoctamin-1 (ANO1), a known ICC marker, shows that ICCs are already present throughout the gut, as from embryonic day (E)7. We devised a protocol to reveal ICC oscillatory and propagative calcium activity in embryonic gut whole mount and found that the first steady calcium oscillations in ICCs occur on (E14). We show that the activation of ICCs leads to an increase in contractile wave frequency, regularity, directionality, and velocity between E12 and E14. We finally demonstrate that application of the c-KIT antagonist imatinib mesylate in organ culture specifically depletes the ICC network and inhibits the transition to a regular rhythmic wave pattern. We compare our findings to existing results in the mouse and predict that a similar transition should take place in the human fetus between 12 and 14 wk of development. Together, our results point to an abrupt physiological transition from smooth muscle mesenchyme self-initiating waves to ICC-driven motility in the fetus and clarify the contribution of ICCs to the contractile wave pattern.NEW & NOTEWORTHY We reveal a sharp transition from smooth muscle to interstitial cell of Cajal (ICC)-driven motility in the chicken embryo, leading to higher-frequency, more rhythmic contractile waves. We predict the transition to happen between 12 and 14 embryonic wk in humans. We image for the first time the onset of ICC activity in an embryonic gut by calcium imaging. We show the first KIT and anoctamin-1 (ANO1) in situ hybridization micrographs in the embryonic chicken gut.

Connexin37-Dependent Mechanisms Selectively Contribute to Modulate Angiotensin II -Mediated Hypertension

Background Gap junction channels made of Connexin37 (Cx37) are expressed by aortic endothelial and smooth muscle cells of hypertensive mice, as well as by the renin-secreting cells of kidneys. Methods and Results To decipher whether Cx37 has any role in hypertension, angiotensin II (Ang II ) was infused in normotensive wild-type and Cx37-deficient mice (Cx37-/-). After 2 to 4 weeks, the resulting increase in blood pressure was lower in Cx37-/- than in wild-type mice, suggesting an alteration in the Ang II response. To investigate this possibility, mice were submitted to a 2-kidney, 1-clip procedure, a renin-dependent model of hypertension. Two weeks after this clipping, Cx37-/- mice were less hypertensive than wild-type mice and, 2 weeks later, their blood pressure had returned to control values, in spite of abnormally high plasma renin levels. In contrast, Cx37-/- and wild-type mice that received N-nitro-l-arginine-methyl-ester, a renin-independent model of hypertension, featured a similar and sustained increase in blood pressure. The data indicate that loss of Cx37 selectively altered the Ang II -dependent pathways. Consistent with this conclusion, aortas of Cx37-/- mice featured an increased basal expression of the Ang II type 2 receptors ( AT 2R), and increased transcripts levels of downstream signaling proteins, such as Cnksr1 and Ptpn6 ( SHP -1). Accordingly, the response of Cx37-/- mice aortas to an ex vivo Ang II exposure was altered, since phosphorylation levels of several proteins of the Ang II pathway ( MLC 2, ERK , and AKT ) remained unchanged. Conclusions These findings provide evidence that Cx37 selectively influences Ang II signaling, mostly via a modulation of the expression of the Ang II type 2 receptor.

The first digestive movements in the embryo are mediated by mechanosensitive smooth muscle calcium waves

Peristalsis enables transport of the food bolus in the gut. Here, I show by dynamic ex vivo intra-cellular calcium imaging on living embryonic gut explants that the most primitive form of peristalsis that occurs in the embryo is the result of inter-cellular, gap-junction-dependent calcium waves that propagate in the circular smooth muscle layer. I show that the embryonic gut is an intrinsically mechanosensitive organ, as the slightest externally applied mechanical stimulus triggers contractile waves. This dynamic response is an embryonic precursor of the 'law of the intestine' (peristaltic reflex). I show how characteristic features of early peristalsis such as counter-propagating wave annihilation, mechanosensitivity and nucleation after wounding all result from known properties of calcium waves. I finally demonstrate that inter-cellular mechanical tension does not play a role in the propagation mechanism of gut contractile waves, unlike what has been recently shown for the embryonic heartbeat. Calcium waves are a ubiquitous dynamic signalling mechanism in biology: here I show that they are the foundation of digestive movements in the developing embryo.This article is part of the Theo Murphy meeting issue on 'Mechanics of development'.