strychnine and cesium-chloride

Airway smooth muscle (ASM) contraction is an important component of the pathophysiology of asthma. Taurine, an agonist of glycine receptor chloride (GlyR Cl(-)) channels, was found to relax contracted ASM, which led us to question whether functional GlyR Cl(-) channels are expressed in ASM. Messenger RNA for β (GLRB), α1 (GLRA1), α2 (GLRA2), and α4 (GLRA4) subunits were found in human (Homo sapiens) and guinea pig (Cavia porcellus) tracheal smooth muscle. Immunoblotting confirmed the protein expression of GLRA1 and GLRB subunits in ASM. Electrical activity of cultured human ASM cells was assessed using a fluorescent potentiometric dye and electrophysiological recordings. Glycine increased current and significantly increased fluorescence in a dose-dependent manner. The GlyR Cl(-) channel antagonist strychnine significantly blocked the effects of glycine on potentiometric fluorescence in ASM cells. Guinea pig airway ring relaxation of ACh-induced contractions by isoproterenol was significantly left-shifted in the presence of glycine. This effect of glycine was blocked by pretreatment with the GlyR Cl(-) channel antagonist strychnine. Glycine treatment during tachykinin- and acetylcholine-induced contractions significantly decreased the maintenance of muscle force compared to control. GlyR Cl(-) channels are expressed on ASM and regulate smooth muscle force and offer a novel target for therapeutic relaxation of ASM.

Topics: Acetylcholine; Animals; Cells, Cultured; Cesium; Chlorides; Electrophysiology; Glycine; Guinea Pigs; Humans; Immunoblotting; Isoproterenol; Membrane Potentials; Muscle Contraction; Muscle Relaxation; Muscle, Smooth; Neurokinin A; Receptors, Glycine; Respiratory System; Reverse Transcriptase Polymerase Chain Reaction; Strychnine

The principal cells of the chick tangential nucleus are vestibular nucleus neurons participating in the vestibuloocular and vestibulocollic reflexes. In birds and mammals, spontaneous and stimulus-evoked firing of action potentials is essential for vestibular nucleus neurons to generate mature vestibular reflex activity. The emergence of spike-firing pattern and the underlying ion channels were studied in morphologically-identified principal cells using whole-cell patch-clamp recordings from brain slices of late-term embryos (embryonic day 16) and hatchling chickens (hatching day 1 and hatching day 5). Spontaneous spike activity emerged around the perinatal period, since at embryonic day 16 none of the principal cells generated spontaneous action potentials. However, at hatching day 1, 50% of the cells fired spontaneously (range, 3 to 32 spikes/s), which depended on synaptic transmission in most cells. By hatching day 5, 80% of the principal cells could fire action potentials spontaneously (range, 5 to 80 spikes/s), and this activity was independent of synaptic transmission and showed faster kinetics than at hatching day 1. Repetitive firing in response to depolarizing pulses appeared in the principal cells starting around embryonic day 16, when <20% of the neurons fired repetitively. However, almost 90% of the principal cells exhibited repetitive firing on depolarization at hatching day 1, and 100% by hatching day 5. From embryonic day 16 to hatching day 5, the gain for evoked spike firing increased almost 10-fold. At hatching day 5, a persistent sodium channel was essential for the generation of spontaneous spike activity, while a small conductance, calcium-dependent potassium current modulated both the spontaneous and evoked spike firing activity. Altogether, these in vitro studies showed that during the perinatal period, the principal cells switched from displaying no spontaneous spike activity at resting membrane potential and generating one spike on depolarization to the tonic firing of spontaneous and evoked action potentials.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Apamin; Bicuculline; Cesium; Chick Embryo; Chlorides; Dose-Response Relationship, Radiation; Drug Combinations; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; In Vitro Techniques; Lysine; Neurons; Sodium Channel Blockers; Strychnine; Tetrodotoxin; Vestibular Nuclei