Secondary Active Transport In secondary active transport the energy is derived secondarily from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances between the two sides of a cell membrane created originally by primary active transport.

Co Transport Sodium Glucose Co transport Sodium Amino acid Co transport

Sodium Glucose Co - transport

Counter Transport Sodium calcium counter transport Sodium Hydrogen counter transport

MEMBRANE POTENTIALS

OBJECTIVES At the end of this lecture you should know: 1. Ionic distribution across the cell membrane 2. Different types of channels present in the cell membrane. 3. Role of different ions in the development of Resting Membrane Potential

Excitable Tissues -Muscle Definition: Imp. Tissues which are capable of responding to stimuli to highest degree than other tissues of the body in the form of electrical signals. Imp. Excitable tissues have LOW Threshold of Stimulation -Nerve -Muscle

Resting Membrane Potential Definition Potential difference existing across the cell membrane under resting condition .

Distribution of Ions across the membrane Na+ mainly extracellular--- 142 mEq/L K+ mainly intracellular----- 140 mEq/L Cl- mainly extra cellular– 108 mEq/L Non-diffusible intracellular anions. -- HPO4 – -- SO4-- ---Intracellular proteins (4 times as in the plasma) Proteins x 10 times HPO4--

Types of Channels in the cell Membrane Na+ * Leak Channels (Slow) K+ -Voltage gated channels ( Fast ) — For Na+ & K+ Slow Ca++ - Na+ Channels -Ligand Gated Channels --- Neurotransmitters, Hormones Na+, K+ & Cl- channels -Na+ - K+ Pump ( ATP ase ) -Mechanical Gated Channels – Hair Cells ( inner Ear)

Leak Channels Why K+ Leak Channels are More Permeable than Na+ Leak Channels 0.5 x 0.3 nm 0.3 x 0.3 nm Na+ K+

Nernst Potential EMF = ± 61 x log (Cin / Cout) The potential across the cell membrane at which the net diffusion of ions across the cell membrane due to concentration gradient stops. Nernst Equation: EMF = ± 61 x log (Cin / Cout) Where 61 is constant & is = RT / z F Where R= Universal Gas constt T = Absolute Temp, z = ion Valence F = Faraday, an electrical Constt

Equilibrium (Nernst) Potential for Na+ Na+ outside = 142 m Eq/L } 61x log 0.1 = +61mv Na+ inside = 14 m Eq/L

Equilibrium(Nernst) Potential for K+ K+ outside = 4.0 m Eq/L }61x log 35= –94mv K+ inside = 140 m Eq/L

Na+ - K+ PUMP (ATPase) Intracellular portion of alpha subunit has: Na+ binding site (1), Phosphorylation site (4) an ATP binding site (5). Extracellular portion has : K+ binding site (2) & Ouabain site (3)

Contribution of Na+-K+ Pump (ATPase) -4mv

Functions of Na+ - K+ Pump (ATPase) 1. As an Enzyme (Cleaves ATP to ADP) 2. Electrogenic. (Contributes -4mv in RMP) 3. Homeostasis of Main Electrolytes and Water & hence volume of the cell. Hormones Increasing functions of ATPase -Thyroxin, Aldosterone & Insulin. - Dopamin decreases its function

Goldman Hodgkin-Katz- Equation EMF(mv)= CNa+ in PNa+ + CK+ in PK+ + CCl-out PCl- -61. Log CNa+ out PNa+ + CK+out PK+ + CCl- inPCl- Where ‘C’=Concentration P= Permeability

Goldman Hodgkin-Katz- Equation Is used to calculate the Diffusion potential when the membrane is permeable to different ions . 1.Polarity of electrical charge. 2.Permeability of the membrane to ions. 3.Concentration of the respective ion on inside or outside

Resting Membrane Potential in Various Excitable Tissues Large Mylinated Nerve fibers Skeletal Muscle Fibers = -90mv Ventricular Muscle fibers Smooth Muscle fiber & } = -55 o -60 mv Self Excitatory Tissues

Measurement of RMP

Types of Disturbances across the Cell Membrane TWO Types: Non-Propagated Potentials. - Synaptic - Generator Catelectrotonic - Electrotonic { Anelctrotonic Propagated – Action Potential

ACTION POTENTIAL Definition: c. Chemical Abrupt / sudden Change (reversal) in resting membrane potential in response to a threshold stimulus. Stimulus: Defn: “Any Change in the environment” TYPES: a. Electrical b. Mechanical c. Chemical

Phases of Action Potential -Polarized state (Resting membrane Potential) -Depolarization - Repolarization -Positive After Potential (After-Hyper polarization)

Types of Channels involved in Various Excitable Tissues Voltage gated channels (fast) ----- Na / K Slow Ca++- Na+ Channels Ligand Gated Channels Na+ - K+ Pump Mechanical Gated Channels (Hair Cells )

Voltage Gated Na+ Channels

Voltage Gated Na+ Channels

Voltage Gated K+ Channels

Action Potential in Large Myelinated Nerve fiber

Action Potential with Plateau (Cardiac Muscle) Red curve shows rise and fall in tension of ventricular myocyte

Action Potential in Self Excitatory Tissues(S-A Node) -55- -55 Diastolic DepolarizationDepolarization)

Action Potential in Smooth Muscle

Compound Action Potential

Biphasic Action Potential (Both electrodes are outside the membrane)

Recording of Membrane and Action Potential

Propagation (Transmission) of Action Potential Electrotonic Conduction.

Propagation of Action Potential-II (Saltatory Conduction) 2000-12000 channels/ Sq Micro Meter

(Saltatory Conduction) 2000-12000 channel/ Sq Micro Meter