Effects of ammonium on ion channels and transporters in colonic secretory cells

Physiology of Electrolyte Transport in the Gut: Implications for Disease

We now have an increased understanding of the genetics, cell biology, and physiology of electrolyte transport processes in the mammalian intestine, due to the availability of sophisticated methodologies ranging from genome wide association studies to CRISPR-CAS technology, stem cell-derived organoids, 3D microscopy, electron cryomicroscopy, single cell RNA sequencing, transgenic methodologies, and tools to manipulate cellular processes at a molecular level. This knowledge has simultaneously underscored the complexity of biological systems and the interdependence of multiple regulatory systems. In addition to the plethora of mammalian neurohumoral factors and their cross talk, advances in pyrosequencing and metagenomic analyses have highlighted the relevance of the microbiome to intestinal regulation. This article provides an overview of our current understanding of electrolyte transport processes in the small and large intestine, their regulation in health and how dysregulation at multiple levels can result in disease. Intestinal electrolyte transport is a balance of ion secretory and ion absorptive processes, all exquisitely dependent on the basolateral Na⁺ /K⁺ ATPase; when this balance goes awry, it can result in diarrhea or in constipation. The key transporters involved in secretion are the apical membrane Cl^- channels and the basolateral Na⁺ -K⁺ -2Cl^- cotransporter, NKCC1 and K⁺ channels. Absorption chiefly involves apical membrane Na⁺ /H⁺ exchangers and Cl^- /HCO₃ ^- exchangers in the small intestine and proximal colon and Na⁺ channels in the distal colon. Key examples of our current understanding of infectious, inflammatory, and genetic diarrheal diseases and of constipation are provided. © 2019 American Physiological Society. Compr Physiol 9:947-1023, 2019.

Ammonium chloride alters neuronal excitability and synaptic vesicle release

Genetically encoded pH-sensors are widely used in studying cell membrane trafficking and membrane protein turnover because they render exo-/endocytosis-associated pH changes to fluorescent signals. For imaging and analysis purposes, high concentration ammonium chloride is routinely used to alkalize intracellular membrane compartments under the assumption that it does not cause long-term effects on cellular processes being studied like neurotransmission. However, pathological studies about hyperammonemia have shown that ammonium is toxic to brain cells especially astrocytes and neurons. Here, we focus on ammonium’s physiological impacts on neurons including membrane potential, cytosolic Ca²⁺ and synaptic vesicles. We have found that extracellularly applied ammonium chloride as low as 5 mM causes intracellular Ca²⁺-increase and a reduction of vesicle release even after washout. The often-used 50 mM ammonium chloride causes more extensive and persistent changes, including membrane depolarization, prolonged elevation of intracellular Ca²⁺ and diminution of releasable synaptic vesicles. Our findings not only help to bridge the discrepancies in previous studies about synaptic vesicle release using those pH-sensors or other vesicle specific reporters, but also suggest an intriguing relationship between intracellular pH and neurotransmission.

Nematocyst discharge in Pelagia noctiluca (Cnidaria, Scyphozoa) oral arms can be affected by lidocaine, ethanol, ammonia and acetic acid

Nematocyst discharge and concomitant delivery of toxins is triggered to perform both defence and predation strategies in Cnidarians, and may lead to serious local and systemic reactions in humans. Pelagia noctiluca (Cnidaria, Scyphozoa) is a jellyfish particularly abundant in the Strait of Messina (Italy). After accidental contact with this jellyfish, not discharged nematocysts or even fragments of tentacles or oral arms may tightly adhere to the human skin and, following discharge, severely increase pain and the other adverse consequences of the sting. The aim of the present study is to verify if the local anesthetic lidocaine and other compounds, like alcohols, acetic acid and ammonia, known to provide pain relief after jellyfish stings, may also affect in situ discharge of nematocysts. Discharge was induced by a combined physico-chemical stimulation of oral arms by chemosensitizers (such as N-acetylated sugars, aminoacids, proteins and nucleotides), in the presence or absence of 1% lidocaine, 70% ethanol, 5% acetic acid or 20% ammonia, followed by mechanical stimulation by a non-vibrating test probe. The above mentioned compounds failed to induce discharge per se, and dramatically impaired the chemosensitizer-induced discharge response. We therefore suggest that prompt local treatment of the stung epidermis with lidocaine, acetic acid, ethanol and ammonia may provide substantial pain relief and help in reducing possible harmful local and systemic adverse reaction following accidental contact with P. noctiluca specimens.