A study of excitatory neuromuscular transmission in the bovine trachea

Abstract

1. The excitatory innervation of bovine tracheal smooth muscle has been studied with the sucrose‐gap apparatus. 2. Single 2 ms electrical stimuli applied to the whole tissue excited intrinsic nerves, and produced a small transient depolarization of the smooth muscle, the excitatory junction potential (e.j.p.). The e.j.p. caused a twitch‐type contraction; twitches and e.j.p.s summated during repetitive stimulation but facilitation was not observed, and action potentials were never elicited. 3. The effects of electrical stimulation could be abolished by atropine (5 × 10−7 mol/l) and augmented by neostigmine (4 × 10−6 mol/l), and were mimicked by exogenous acetylcholine (1·0 μg/ml). 4. With the electron microscope, the density of innervation was found to be low (one axon per ninety smooth muscle cells). Axons were found in small groups in the clefts between bundles of cells, but no axons penetrated within the muscle bundles. Naked axon varicosities containing agranular vesicles were seen, but no axon approached within 200 nm of a smooth muscle cell. 5. It is difficult to reconcile the sparsity of innervation with the dependence of the tissue on nerve excitation to initiate activity.

Spontaneous Activity in the Trachea of Dogs Treated With Indomethacin: An Experimental Model for Aspirin‐related Asthma

“…Apparatus and experimental procedures for the microelectrode, the double sucrose gap or tension recording methods were the same as those described by Ito & Tajima (1981) In the control dog trachea, these spontaneous contractions were not observed, and similar observations have been made by other workers (Kirkpatrick, 1975;Suzuki, Morita & Kuriyama, 1976;Cameron & Kirkpatrick, 1977).…”

“…These findings in the ileal or tracheal smooth muscle indicate that agents which depolarize the membrane to within a particular range could initiate such oscillations in the membrane potential. In the bovine trachea, oscillatory potentials were observed when the membrane depolarization induced by acetylcholine had reached a level of 12 mV, as measured by the sucrose-gap method (Cameron & Kirkpatrick, 1977).…”

The spontaneous electrical and mechanical activity of human bronchial smooth muscle: its modulation by drugs

“…Further, it is also conceivable that spontaneous contractions are artifactual due to the mediators released from the tissues by trauma during the preparative procedures. In accord with this, oscillations in membrane potential and subsequent spontaneous contractions have been observed in response to histamine (Kirkpatrick 1975) acetylcholine (Cameron & Kirkpatrick, 1977), 5-hydroxytryptamine (Coburn & Yamaguchi, 1977) or after prolonged treatment with indomethacin (Ito & Tajima, 1981b) in bovine or dog trachea. In the present experiments FPL 55712, indomethacin or atropine suppressed the slow waves and spontaneous contractions.…”

Actions of indomethacin and prostaglandins on neuroeffector transmission in the dog trachea

“…Cameron & Kirkpatrick (1977) using the double sucrose gap method also reported findings of a long latency and prolonged duration of e.j.p.s in tissues from the bovine trachea and concluded that the latency was partly due to the conduction time down to the fine nerve terminals from the stimulus site to the interface between Krebs solution and sucrose (a distance of 3 mm). In the present experiments, the minimum latency required to generate the e.j.p.…”

“…Since the innervation of the muscle tissues is reportedly sparse in the case of bovine or dog trachea (Suzuki et al 1976;Cameron & Kirkpatrick, 1977), diffuse liberations of transmitters may partly explain the long latency and the slow rising and falling phases of the e.j.p. Furthermore, it is known that a long latency is one of the characteristics of muscarinic responses in many tissues (Purves, 1976).…”