* Secondary active transport Membrane protein: pump+transporter Forms: symport & antiport
* Exocytosis & endocytosis Exocytosis: cell secretion Endocytosis: phagocytosis Receptor mediated endocytosis
Sodium-potassium pump
Secondary active transport
Exocytosis & endocytosis
Receptor mediated endocytosis
ቤተ መጻሕፍቲ ባይዱ
§ 2. Transmembrane signal transduction Concept Several main forms * Mediated by ion channel * Mediated by G-protein coupled receptor * Mediated by tyrosine kinase receptor * Mediated by intercellular channel * Mediated by nitric oxide Cellular proto-oncogene Mediate-early gene
* Along an unmyelinated fiber * Along a myelinated fiber
Saltatory conduction faster than that along an unmyrlinated fiber Energy-sparing principle
Conduction of AP along an unmyelinated fiber
Fluid mosaic model of membrane
* Simple diffusion & its energy source O2, CO2, NH3, NO, etc.
* Facilitated diffusion & its characteristics Facilitated diffusion via ion channel Chemically gated channel Voltage-gated channel Mechanically gated channel Na+, K+, Ca2+, Cl channel Facilitated diffusion via carrier Glucose, amino acids, some ions, etc.
Tyrosine kinase receptor mediated transduction
§ 3. Bioelectrical phenomena of the cell
Several basic concepts * Excitability * Excitable cells or tissues * Stimulus & excitation * Threshold stimulus, intensity or threshold * Relationship between Excitability & threshold
Definition & Characteristics: Gradational, electrotonic propagation, summation (spatial & temporal ~)
* Threshold potential——firing level Definition
* Initiation of action potential Threshold stimulus or Several subthreshold stimulidepolarizationfiring level
between intra- & extra-cellular fluids
* Variations in membrane permeability to
those ions during rest
* Outward diffusion of K+EK
EK

RT ln PK [K ]O ZF PK [K ]i
* Action potential (AP) Occurs when a stimulus is applied A brief deflection (spike) of the baseline Depolarization & repolarization phases All or none & not attenuated propagation
Sodium pump’s work recovery of the distribution of [K+]i & [Na+]O
Several physiological terms * Polarization * Depolarization * Overshoot * Repolarization * Hyperpolarization * Spike & after-potential Negative & positive after-potential
Local response
Local response and its contribution to AP
Conduction of action potential Mechanism: local current Characteristics: In both directions
Facilitated diffusion via ion channel
Facilitated diffusion via carrier
* Active transport Sodium-potassium pump & its effects Other pumps: calcium pump, proton pump
* Na+ channel has 3 states Resting, active & inactive states
Three states of Na+ channel
Experimental evidence * Voltage clamp technique By Hodgkin & Huxley in ’1940 Principle: GNa=1/RNa=INa/(EmENa) GK=1/RK=IK/(EmEK) * Combined with pharmacological technique Na+ channel blocker: tetrodotoxin (TTX) K+ channel blocker: tetraethylammonium (TEA) * Patch clamp technique By Neher & Sakmann in 1976
Voltage clamp
Membrane current
Changes of membrane conductance during AP
Patch Clamp
Records with the technique of patch clamp
Local response & threshold potential T * Local response
* Mediated by ion channel Ionotropic receptor
* Mediated by G-protein coupled receptor Metabotropic receptor, G-protein, effecter enzyme AC-cAMP-PKA PLC-IP3-Ca2+-CaM & PLC-DG-PKC G-protein-ion channel
* Mediated by tyrosine kinase receptor Tyrosine kinase receptor receptor-associated tyrosine kinase
A model of G-protein coupled receptor
G-protein coupled receptor mediated transduction
* Transmembrane diffusion of other ions
Em

RT ln PK [K ]O PNa[Na ]O PCl[Cl ]i ZF PK [K ]i PNa[Na ]i PCl[Cl ]O
* Electrogenesis of sodium pump
Genesis of action potential * Depolarization phase Membrane permeability to Na+ENa Depolarization+overshoot * Repolarization phase Membrane permeability to Na+ Membrane permeability to K+Em Repolarization * After repolarization (resting phase)
The further mechanism Why does the membrane permeability change when the cell receives a stimulus?
* Na+ channel is voltage dependent Stimulusa few Na+ channels open membrane depolarizationwhen reached the firing levela great amount of Na+ channels open (regenerative cycle) APs burst