The ER synthesizes lipids for building cell membranes and performing cellular functions such as energy storage and signaling. The lipid synthesis machinery embedded in the ER membrane primarily collects all reactants from the cytosol. Following synthesis, the secretory pathway and the ER contact sites distribute these lipids to other cellular organelles. Additionally, the energy-rich triacylglycerides are transported from the ER via lipid droplets.
The major components of all eukaryotic cell...

Cholinergic neurotransmission involves the synthesis and the release of acetylcholine (ACh) in order to transmit nerve impulses across the synapse. The process begins with the synthesis of acetyl CoA, a precursor for ACh, from ATP, acetate, and coenzyme A in the mitochondria. Choline, another vital precursor, is transported inside the neuron through choline transporters, including high-affinity choline transporter CHT1, low-affinity choline transporter CTL1, and lower-affinity choline...

Cognitive enhancers, also known as "smart drugs," are substances used to enhance memory, mental alertness, and concentration. These can be natural or synthetic and improve cognition in conditions like Alzheimer's disease (AD) and other neurodegenerative diseases. Some common examples include caffeine, amphetamines, methylphenidate, modafinil, arecoline, donepezil, vortioxetine, and piracetam. These enhancers work on the principle of synaptic plasticity and altered circuit function.

Direct-acting cholinergic agonists, such as synthetic choline esters and naturally occurring alkaloids, exert their effects by enhancing the actions of acetylcholine and stimulating the parasympathetic nervous system. Synthetic choline esters share structural similarities with acetylcholine. For example, they have a positively charged quaternary ammonium or onium group, contributing to their hydrophilic characteristics. As a result, they are poorly absorbed in the body through oral...

Cholinesterases are a group of serine hydrolase enzymes that play a crucial role in the breakdown of choline esters. The two primary types of cholinesterases are acetylcholinesterases (AChEs) and butyrylcholinesterase (BuChEs), which differ in their distribution, function, and substrate specificity. AChEs, also known as true cholinesterases, specifically hydrolyze acetylcholine, while BuChEs, often referred to as pseudocholinesterases, can hydrolyze various choline esters, including...

Cholinergic antagonists—such as antimuscarinics—are available in oral, topical, ocular, parenteral, and inhalational formulations. Most antimuscarinics are oral formulations,  while scopolamine is available as a topical patch, and ipratropium and tiotropium are available as inhalation aerosols or powders. Atropine, tropicamide, and cyclopentolate are topically instilled in the eye. Most antimuscarinics are lipid-soluble and readily absorbed from the gastrointestinal tract and...