Gated Ion Channels:- Neurons Have Receptor Channels That Respond to Different Neurotransmitters

Animal cells, especially those of the nervous system, contain a variety of ion channels gated by ligands, voltage, or both. The neurotransmitters 5-hydroxytryptamine (serotonin), glutamate, and glycine can all act through receptor channels that are structurally related to the acetylcholine receptor. Serotonin and glutamate trigger the opening of cation (K⁺, Na⁺, Ca²⁺) channels, whereas glycine opens Cl-specific channels. Cation and anion channels are distinguished by subtle differences in the amino acid residues that line the hydrophilic channel. Cation channels have negatively charged Glu and Asp side chains at crucial positions. When a few of these acidic residues are experimentally replaced with basic residues, the cation channel is converted to an anion channel. Depending on which ion passes through a channel, the ligand (neurotransmitter) for that channel either de polarizes or hyperpolarizes the target cell. A single neuron normally receives input from several (or many) other neurons, each releasing its own characteristic neurotransmitter with its characteristic depolarizing or hyperpolarizing effect. The target cell’s Vm therefore reflects the integrated input (Fig. 12–1d) from multiple neurons. The cell responds with an action potential only if the integrated input adds up to a net depolarization of sufficient size. The receptor channels for acetylcholine, glycine, glutamate, and -aminobutyric acid (GABA) are gated by extracellular ligands. Intracellular second messengers—such as cAMP, cGMP (3,5-cyclic GMP, a close analog of cAMP), IP3 (inositol 1,4,5-trisphosphate), Ca²⁺, and ATP—regulate ion channels of another class, which, as we shall see in Section 12.7, participate in the sensory transductions of vision, olfaction, and gustation.

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علامات مبكرة للإيبولا يمكن الخلط بينها وبين الإنفلونزا

خبراء: الفيروسات مثل هانتا وإيبولا أصبحت أكثر شيوعا وفتكاً

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مهمة فضائية "أوروبية صينية" لكشف أسرار الرياح الشمسية

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مواضيع ذات صلة

Solute Transport across Membranes:-The β-Adrenergic Receptor Is Desensitized by Phosphorylation

G Protein–Coupled Receptors and Second Messengers:-The -Adrenergic Receptor System Acts through the Second Messenger cAMP

Receptor Enzymes:- Receptor Guanylyl Cyclases Generate the Second Messenger cGMP

Receptor Enzymes: -The Insulin Receptor Is a Tyrosine-Specific Protein Kinase

Gated Ion Channels:- Voltage-Gated Ion Channels Produce Neuronal Action Potentials

Gated Ion Channels:- Ion Channels Underlie Electrical Signaling in Excitable Cells

Solute Transport across Membranes:- Defective Ion Channels Can Have Adverse Physiological Consequences

Solute Transport across Membranes:- The Acetylcholine Receptor Is a Ligand-Gated Ion Channel

Solute Transport across Membranes:- The Neuronal Na+ Channel Is a Voltage-Gated Ion Channel

Solute Transport across Membranes: -The Structure of a K+ Channel Reveals the Basis for Its Specificity

Solute Transport across Membranes:- Ion-Channel Function Is Measured Electrically

Solute Transport across Membranes:- Ion-Selective Channels Allow Rapid Movement of Ions across Membranes