An acetylcholine-like substance and cholinesterase in the smooth muscle of the chick amnion

Diverse contribution of amniogenic somatopleural cells to cardiovascular development: With special reference to thyroid vasculature

BACKGROUND

The somatopleure serves as the primordium of the amnion, an extraembryonic membrane surrounding the embryo. Recently, we have reported that amniogenic somatopleural cells (ASCs) not only form the amnion but also migrate into the embryo and differentiate into cardiomyocytes and vascular endothelial cells. However, detailed differentiation processes and final distributions of these intra-embryonic ASCs (hereafter referred to as iASCs) remain largely unknown.

RESULTS

By quail-chick chimera analysis, we here show that iASCs differentiate into various cell types including cardiomyocytes, smooth muscle cells, cardiac interstitial cells, and vascular endothelial cells. In the pharyngeal region, they distribute selectively into the thyroid gland and differentiate into vascular endothelial cells to form intra-thyroid vasculature. Explant culture experiments indicated sequential requirement of fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) signaling for endothelial differentiation of iASCs. Single-cell transcriptome analysis further revealed heterogeneity and the presence of hemangioblast-like cell population within ASCs, with a switch from FGF to VEGF receptor gene expression.

CONCLUSION

The present study demonstrates novel roles of ASCss especially in heart and thyroid development. It will provide a novel clue for understanding the cardiovascular development of amniotes from embryological and evolutionary perspectives.

SOME EFFECTS OF ATROPINE ON SMOOTH MUSCLE

Contractions of the nerve-free smooth muscle of the chick amnion, either spontaneous or in response to electrical or mechanical stimuli, are potentiated by high conentrations (10(-5) g/ml.) of atropine sulphate. In addition hyoscine, homatropine, lachesine, propantheline bromide and atropine N-methyl and atropine N-butyl salts potentiate spontaneous activity in the amnion. The effects of atropine do not appear to depend on inhibition of cholinesterase; on labilization, stabilization or depolarization of the muscle cell membrane; or on an increase in metabolism. It is suggested that the effects are the result of blockade of the muscarinic acetylcholine receptors. The way in which this may facilitate the conducted response is discussed.

The action of neurotransmitter hormones and analogues and cyclic nucleotides and theophylline on electrolyte transport by the excretory duct of the rabbit mandibular gland

The effects of autonomic drugs on electrolyte transport by the main duct of the rabbit mandibular gland were studied in vitro. Acetylcholine, in concentrations as low as 10(-10) M, reduced nett Na+ reabsorption and partially depolarized the transepithelial potential difference (P.D.); the effects were blocked by atropine. Acetylcholine was relatively ineffective applied from the luminal rather than the interstitial surface of the duct. Noradrenaline and isoproterenol produced similar effects to acetylcholine but the minimum effective concentrations were much higher (10(-7) M and 10(-3) M, respectively). It was concluded that the duct cells possessed specific muscarinic receptors on the basal cell membrane but that adrenergic receptors, particularly beta receptors, were either scanty or lacking altogether. Theophylline (10(-5) M) could mimic the effects of the autonomic drugs and produced a dramatic potentiation of the action of acetylcholine. Both cAMP and cGMP (4 times 10(-5) M) mimicked the acetylcholine response but cAMP was only effective when applied to the luminal cell membrane. It is proposed that cAMP is the intracellular mediator of the acetylcholine response and that it produces some of its effects by acting on an enzyme system close to the apical cell membrane.

The action of physostigmine and the distribution of cholinesterases in the chicken oesophagus

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