SUMMARY1. The smooth muscle layer of the bovine trachea was studied in vitro with the micro-electrode and sucrose-gap techniques. The membrane potential was stable at -47-6 + 0-98 (S.E. of mean) mV, and there was no spontaneous electrical or mechanical activity.2. The cell membrane had strong rectifying properties, making it impossible to elicit action potentials by electrical stimulation in normal Krebs solution. The rectification was abolished by TEA (30 mmol/l), which depolarized the membrane and produced plateau-type action potentials.3. The spontaneous repetitive action potentials produced by TEA were associated with rhythmic oscillatory contractions of the muscle strips.4. Histamine caused an increased tone, with superimposed rhythmic fluctuations in tension. The electrical response consisted of depolarization, with rhythmic slow oscillations in potential (slow waves) which were synchronous with the fluctuations in tension.5. Acetylcholine produced smooth, tonic contractures of tracheal muscle strips, and caused simple depolarization of the membrane. No action potentials were recorded.6. In calcium-free solutions containing EGTA, the mechanical response to TEA was completely abolished; the response to histamine was greatly reduced; the response to acetylcholine was reduced to a lesser extent. All responses reverted to normal when normal concentrations of extracellular calcium were restored.7. Lanthanum added to the bathing solution abolished the contraction due to TEA even though the solution contained calcium. It reduced the histamine-induced contraction to 26 % of control, and reduced the acetylcholine-induced contraction to 58 % of control; extracellular calcium was present throughout.

SUMMARYThe effect of inhibitory nerve stimulation on the mechanical, membrane potential and membrane conductance responses of isolated bovine tracheal smooth muscle has been studied.Membrane responses were measured in a sucrose-gap apparatus. In order to record inhibitory responses, it was necessary to increase tone in the preparation by applying a drug such as histamine. When tone was raised, repetitive field stimulation of intrinsic nerves caused depolarization and contraction, followed by relaxation and a suppression of histamine-induced slow waves. Hyperpolarization of the membrane was only seen following prolonged nerve stimulation, and there was no change in membrane conductance. The inhibitory effect of nerve stimulation was abolished by tetrodotoxin, but was not abolished by atropine, indomethacin, propranolol, naloxone or the purinergic blockers quinidine and theophylline. It was not satisfactorily mimicked by catecholamines, by y-amino-n-butyric acid (GABA) or by purines.Nerves with catecholamine fluorescence could not be found in the tracheal muscle layer. Neither adrenergic nor purinergic types of nerve terminal could be found in the tracheal muscle layer during ultrastructural examination of over one thousand nerve profiles. Vasoactive intestinal peptide (VIP) caused relaxation of the histamine-contracted tracheal muscle, suppressed the slow wave and caused slight hyperpolarization at higher concentrations, without affecting the membrane conductance. VIP was found in samples of tracheal muscle at a mean concentration of 1-95 ng/g. When the effluent solution flowing past isolated tracheal muscle strips was assayed for VIP, samples collected during inhibitory nerve stimulation had much higher concentrations ofthe peptide than samples collected before stimulation, after stimulation, or during stimulation in the presence of tetrodotoxin (10-6 mol/l). The VIP content of the effluent during control periods was 73-8 pg/ml, and during stimulation was 167 5 pg/ml. It is suggested that VIP might be the non-adrenergic inhibitory neurotransmitter in bovine tracheal smooth muscle.

Bias associated with the use of NaF-KOx tubes may have a significant impact on the prevalence of fasting hyperglycaemia, according to current diagnostic criteria. The small but significant difference between preanalytical processes should be considered when screening for the presence of diabetes mellitus.

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.

1. The contracture normally induced in isolated bovine tracheal smooth muscle by potassium-rich solution was abolished by removal of the extracellular calcium. The contraction returned when calcium was added to the solution in a concentration greater than 0.05 mmol/l. 2. The amplitudes of the potassium-contracture, and of the contractile responses to histamine and acetylcholine in normal physiological solutions, declined at low temperatures (15-25 degrees C). If drugs were added during the plateau phase of the potassium contracture, the extra tension developed above the contracture did not change with temperature. 3. Calcium-depletion reduced the responses to drugs, and repeated application of the drugs in calcium-free solution produced progressively smaller contractions, suggesting that an intracellular store of calcium was being used up. 4. Depolarization of calcium-depleted tracheal muscle by high-K+ solution without calcium produced responses to drugs which were larger than those in sodium-based calcium-free solutions. There was no potentiation in a solution in which sodium was replaced by sucrose, suggesting that potassium was not acting simply by replacing the sodium. 5. It is suggested that depolarization of the membrane by potassium makes available a fraction of bound calcium which was not available in calcium-free sodium-based solution.