Autonomic modification of intestinal smooth muscle contractility

Abstract

Intestinal smooth muscle contracts rhythmically in the absence of nerve and hormonal stimulation because of the activity of pacemaker cells between and within the muscle layers. This means that the autonomic nervous system modifies rather than initiates intestinal contractions. The practical described here gives students an opportunity to observe this spontaneous activity and its modification by agents associated with parasympathetic and sympathetic nerve activity. A section of the rabbit small intestine is suspended in an organ bath, and the use of a pressure transducer and data-acquisition software allows the measurement of tension generated by the smooth muscle of intestinal walls. The application of the parasympathetic neurotransmitter ACh at varying concentrations allows students to observe an increase in intestinal smooth muscle tone with increasing concentrations of this muscarinic receptor agonist. Construction of a concentration-effect curve allows students to calculate an EC50 value for ACh and consider some basic concepts surrounding receptor occupancy and activation. Application of the hormone epinephrine to the precontracted intestine allows students to observe the inhibitory effects associated with sympathetic nerve activation. Introduction of the drug atropine to the preparation before a maximal concentration of ACh is applied allows students to observe the inhibitory effect of a competitive antagonist on the physiological response to a receptor agonist. The final experiment involves the observation of the depolarizing effect of K(+) on smooth muscle. Students are also invited to consider why the drugs atropine, codeine, loperamide, and botulinum toxin have medicinal uses in the management of gastrointestinal problems.

Relaxant effects of Azadirachta indica A. Juss var. siamensis Valeton flower extract on isolated rat ileum contractions and the mechanisms of action

“…14 Meanwhile, Ach has known to play roles in the excitatory effect of parasympathetic nerves on intestinal smooth muscle. It binds to muscarinic receptors on the smooth muscle cell membrane 15 and thereby increases the activity of phospholipase C which generates inositol triphosphate (IP 3 ). The release of IP 3 from the plasma membrane allowed it to stimulate the release of intracellular Ca 2+ stores and subsequently induce contraction of smooth muscle cells.…”

A virtual experiment improved students’ understanding of physiological experimental processes ahead of a live inquiry-based practical class

“…The communication and social interactions between students and teaching staff during the practical classes encourages collaborative learning and enhances engagement by fostering a student's positive sense of inclusion (6,11). Practical laboratory classes also support the development of research skills, such as experimental design, data analysis, statistics, and report writing; expose students to experimental techniques and methodologies; and facilitate employability skills development, such as communication, quantitative reasoning, problem solving, and team work (15,19). However, when developing practical classes for teaching, consideration needs to be given to the use of animals as subjects (23) and the expense and time commitment for running these classes, especially with large student cohorts and reduced budgets.…”

“…However, when developing practical classes for teaching, consideration needs to be given to the use of animals as subjects (23) and the expense and time commitment for running these classes, especially with large student cohorts and reduced budgets. Furthermore, the busy, social, and noisy environment of the practical class distracts students from the aims and theory of the exercise (11,13) and can result in an over-reliance on practical laboratory notes (19).…”

Anticholinergic, anti‐depressant and other medication use is associated with clinically relevant oesophageal manometric abnormalities

“…SNRIs increase levels of serotonin (5‐HT) and norepinephrine in the synaptic cleft by binding to reuptake transporters. Norepinephrine exerts its effect on the alpha‐2 receptor subtype 13 . In adrenergically denervated opossums, alpha‐adrenergic agonists (including norepinephrine) increased lower oesophageal sphincter pressure, implicating alpha‐adrenergic stimulation in the modulation of basal lower oesophageal sphincter pressure 14 .…”