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

The importance of ion channels to physiological processes is clear from the effects of mutations in specific ion-channel proteins (Table 11–8). Genetic defects in the voltage-gated Na channel of the myocyte plasma membrane result in diseases in which muscles are periodically either paralyzed (as in hyperkalemic periodic paralysis) or stiff (as inparamyotonia congenita). As noted earlier, cystic fibrosis is the result of a mutation that changes one amino acid in the protein CFTR, a Cl ion channel; the defective process here is not neu rotransmission but secretion by various exocrine gland cells whose activities are tied to Cl ion fluxes. Many naturally occurring toxins act on ion channels, and the potency of these toxins further illustrates the importance of normal ion-channel function. Tetrodotoxin (produced by the puffer fish, Sphaeroides rubripes) and saxitoxin (produced by the marine dinoflagellate Gonyaulax, which causes “red tides”) act by binding to the voltage-gated Na channels of neurons and preventing normal action potentials. Puffer fish is an ingredient of the Japanese delicacy fugu, which may be prepared only by chefs specially trained to separate

succulent morsel from deadly poison. Eating shellfish that have fed on Gonyaulaxcan also be fatal; shellfish are not sensitive to saxitoxin, but they concentrate it in their muscles, which become highly poisonous to organ isms higher up the food chain. The venom of the black mamba snake contains dendrotoxin, which interferes with voltage-gated K⁺ channels. Tubocurarine, the active component of curare (used as an arrow poison in the Amazon), and two other toxins from snake venoms, cobrotoxin and bungarotoxin, block the acetylcholine receptor or prevent the opening of its ion channel. By blocking signals from nerves to muscles, all these toxins cause paralysis and possibly death. On the positive side, the extremely high affinity of bungarotoxin for the acetylcholine receptor (K_d=10^-15M) has proved useful experimentally: the radiolabeled toxin was used to quantify the receptor during its purification.

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نظام غذائي شائع قد يؤدي إلى ارتفاع الكوليسترول الضار

تحذيرات هامة من عواقب تناول "أيبوبروفين" مع أدوية شائعة

علامات مبكرة للإيبولا يمكن الخلط بينها وبين الإنفلونزا

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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:- Neurons Have Receptor Channels That Respond to Different Neurotransmitters

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:- 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