Evangelista, Stefano

AbstractBackgroundOtilonium bromide (OB) is used as a spasmolytic drug in the treatment of the functional bowel disorder irritable bowel syndrome. Although its acute effects on colonic relaxation are well‐characterized, little is known about the effects of chronic administration ofOBon enteric neurons, neuromuscular transmission, and interstitial cells of Cajal (ICC), key regulators of the gut function.MethodsAdult Sprague–Dawley rats were treated withOBin drinking water at a dose of 2 mg/kg for 30 days. The colons ofOB‐treated and age‐matched control rats were studied by confocal immunohistochemistry to detect immunoreactivity (IR) in myenteric plexus neurons for nitrergic and tachykininergic markers, and also by microelectrode electrophysiology.Key ResultsUsing immunohistochemistry, chronicOBadministration did not change total neuron number, assessed by anti‐HuIR, but resulted in a significant increase inNK1 receptor positive neurons, a decrease in neuronal nitric oxide synthase expressing neurons, and a reduction in volume of substance P in nerve fibers in the myenteric plexus. ChronicOBadministration potentiated inhibitory and excitatory junction potentials evoked by repetitive electrical field stimulation. The various types of colonicICC, detected by KitIR, were not altered nor were slow waves or smooth muscle membrane potential.Conclusions & InferencesChronic treatment withOBcaused significant changes in the nitrergic and tachykinergic components of the myenteric plexus and in both inhibitory and excitatory neurotransmission in the rat colon.

Antispasmodics are used clinically to treat a variety of gastrointestinal disorders by inhibition of smooth muscle contraction. The main pathway for smooth muscle Ca2+entry is through L-type channels; however, there is increasing evidence that T-type Ca2+channels also play a role in regulating contractility. Otilonium bromide, an antispasmodic, has previously been shown to inhibit L-type Ca2+channels and colonic contractile activity. The objective of this study was to determine whether otilonium bromide also inhibits T-type Ca2+channels. Whole cell currents were recorded by patch-clamp technique from HEK293 cells transfected with cDNAs encoding the T-type Ca2+channels, CaV3.1 (α1G), CaV3.2 (α1H), or CaV3.3 (α1I) alpha subunits. Extracellular solution was exchanged with otilonium bromide (10−8to 10−5M). Otilonium bromide reversibly blocked all T-type Ca2+channels with a significantly greater affinity for CaV3.3 than CaV3.1 or CaV3.2. Additionally, the drug slowed inactivation in CaV3.1 and CaV3.3. Inhibition of T-type Ca2+channels may contribute to inhibition of contractility by otilonium bromide. This may represent a new mechanism of action for antispasmodics and may contribute to the observed increased clinical effectiveness of antispasmodics compared with selective L-type Ca2+channel blockers.