Lecture 5.1 - The Cellular Response to Action Potentials PDF

 MEMBRANES AND RECEPTORS - SESSION 5 ELECTRICAL EXCITABILITY LECTURE 5.1 - THE CELLULAR RESPONSE TO ACTION POTENTIALS Assist.Prof.Dr.Ameera Jasim Clinical Biochemistery AIMS :  To understand how action potentials open Ca2+ channels in cell membranes  To b...

 MEMBRANES AND RECEPTORS - SESSION 5 ELECTRICAL EXCITABILITY LECTURE 5.1 - THE CELLULAR RESPONSE TO ACTION POTENTIALS Assist.Prof.Dr.Ameera Jasim Clinical Biochemistery AIMS :  To understand how action potentials open Ca2+ channels in cell membranes  To be able to describe some aspects of the diversity of Ca2+ channels  To be able to describe events underlying fast synaptic transmission  To be able to describe some properties of ligand gated ion channels, with nicotinic acetylcholine receptors as an example  To understand the action of two types of blockers of nicotinic receptors  Describe some aspects of the diversity of Ca2+ channels A calcium channel is a type of transmembrane ion channel that is permeable to calcium ions. These channels can be gated by either voltage or ligand binding. Voltage-gated calcium channels are opened by depolarization membrane potentials, thereby allowing an influx of calcium ions from outside the cell. There are five types of voltage-gated calcium channels: L-type, P- type, N-type, R-type, and T-type.  Voltage-gated calcium channels (VGCC) are formed as a complex of several different subunits: α1, α2δ, β1-4, and γ. The structure of the α subunit of VGCC is very similar to Voltage-gated sodium channels. Different Ca2+ channels have different primary locations. However, Ca2+ channels have structural diversity – a blocker that blocks one Ca2+ channels will not necessarily block another. Calcium channel blockers, also known as calcium channel antagonists, prevent the flow of calcium ions through the channel. Dihydropyridine (calcium channels blockers) are used clinically as a medication to treat hypertension. Other calcium channel blockers can be used to control heart rate, and reduce chest pain.  Describe events underlying fast synaptic transmission Ligand-gated calcium channels are opened by the binding of a ligand such as a neurotransmitter to the receptor. Types of ligand-gated calcium channels include IP3 receptors, ryanodine receptors, and two-pore channels. how action potentials open Ca2+ channels in cell membranes The arrival of the action potential opens voltage-sensitive calcium channels are located close to vesicle release sites in the presynaptic membrane; the influx of calcium causes vesicles filled with neurotransmitter to migrate to the cell's surface and release their contents in to the synaptic cleft. Describe some properties of ligand gated ion channels, with nicotinic acetylcholine receptors as an example ❑ The nicotinic acetylcholine receptor (nAChR) is an example of a ligand- gated ion channel. ❑ The ACh will bind to (nAChR) on the post-junctional membrane to produce an end-plate potential; this depolarization in turn raises the muscle above threshold so that an action potential is produced in the muscle membrane. Action of two types of blockers of nicotinic receptors ❑ Pharmacological agents that competitively block nicotinic acetylcholine receptors do so by binding at the molecular recognition site for Ach are called competitive blockers such as tubocurarine. ❑ Depolarizing blockers cause a maintained depolarization at the post-junctional membrane. e.g. succinylcholine is used in operation to induce paralysis.  Describe Myasthenia gravis Myasthenia gravis is an autoimmune disease, caused by antibodies directed against nAChR on postsynaptic membrane of skeletal muscle ❑ Patients suffer profound weakness ❑ Weakness increases with exercise ❑ Antibodies lead to loss of functional nAChR by complement mediated lysis and receptor degradation ❑ Endplate potentials are reduced in amplitude leading to muscle weakness and fatigue. ‫إبق قويا ألجل اللحظة اليت حتلم بها كل يوم‬ stay strong for the moment you dream about every day Thanks for listening