Membranes

Question 1

Describe the fluid composition of plasma (mM)

Answer 1

Na+: 142, K+: 4.4, Ca2+: 2.4, Mg2+: 0.9, Cl-: 102, HCO3-: 22, H2PO4-/HPO4(2-): 1.4, proteins: 7 g/L, glucose: 5.5, pH: 7.4, Osmolarity: 291 mosmole/kg H2O

Question 2

Describe the fluid composition of interstitium fluid (mM)

Answer 2

Na+: 145, K+: 4.5, Ca2+: 1.2, Mg2+: 0.55, Cl-: 116, HCO3-: 25, H2PO4-/HPO4(2-): 0.8, proteins: 1 g/L, glucose: 5.9, pH: 7.4, Osmolarity: 290 mosmole/kg H2O

Question 3

Describe the fluid composition of cells (mM)

Answer 3

Na+: 15, K+: 120, Ca2+: 0.0001, Mg2+: 18, Cl-: 20, HCO3-: 16, H2PO4-/HPO4(2-): 0.7, proteins: 30 g/L, glucose: very low, pH: app. 7.2, Osmolarity: 290 mosmole/kg H2O

Question 4

What is isoosmotic?

Answer 4

= 290 mosmole/kg

Question 5

What is hypoosmotic?

Answer 5

< 290 mosmole/kg

Question 6

What is hyperosmotic?

Answer 6

> 290 mosmole/kg

Question 7

Describe the permeability of the plasma membrane.

Answer 7

Permeable: Small nonpolar molecules (O2, CO2, N2, steoroid hormones)
Semi: small uncharged polar molecules (H2O, ethanol, glycerol)
Less: larger uncharged polar molecules (amino acids, glucose, nucleosides)
Not permeable: ions

Question 8

How are ions transported across the membrane?

Answer 8

By membrane proteins (channels/carriers)

Question 9

What does diffusion of charged molecules depend on?

Answer 9

Chemical and voltage differences across membrane (electrochemical gradient)

Question 10

Describe the electrochemical equation.

Answer 10

N = RT * ln ([X]i/[X]o) + zF

Question 11

Through which channels can passive transport happen?

Answer 11

Ion channels (gates), pores (always open), transporters (e.g., GLUT1)

Question 12

Describe Nernst equation at equilibrium.

Answer 12

Ex = Vm = - (RT/zF) ln ([X]i/[X]o)

At 37 degrees: E_x = -61.5/z_x * log ([X]i/[X]o)

Question 13

How do we study ion channels?

Answer 13

Patch-clamp, two-electrode clamp, microelectrodes, flourescent voltage sensors or ion sensors, Ussing chamber, isotope fluxes

Question 14

What kind of transporters is there?

Answer 14

Cotransporters (symport), exchangers (antiport), ABC transporters (ATP binding cassette)

Question 15

How does ABC transporters work?

Answer 15

They bind ATP, but do not hyrdolyze it, can act as pumps, channels and regulators. CFTR is an ABC transporter.

Question 16

What are active membrane transport?

Answer 16

Transport against the electrochemical gratient, requires energy –> bind and hydrolyze ATP (also called ATPases or pumps)

Question 17

What are the functions of the Na/K pump?

Answer 17

• Keeps [Na+]i low and [K+]i high
• Na+ gradient used by many Na+ coupled transporters
• Vm is negative due to high resting Gk and K+ gradient that is set up by the pump
• Keeps the cell volume (high [Na+]i –> H2O influx –> cell swells)

Question 18

What is ouabain?

Answer 18

A Na+/K+ ATPase inhibitor

Question 19

What is the function of membrane transporters?

Answer 19

Na+/K+ pump: maintenance of low

Question 20

What is the function of membrane transporters?

Answer 20

• Na+/K+ pump: maintenance of low [Na+]i and high [K+]i + cell volume
• K+ channels: maintenance of negative Vm
• Ca2+ pump and Na+/Ca2+ exchanger: maintenance of low [Ca2+]i
• NHE, AE, NBC, vacuolar H+ pumps, and K+/H+ pumps: maintenance of pHi
• NKCC, AE and Cl- leak through channels: maintenance of modest [Cl-]i (in neurons, low [Cl-]i is due to K+/Cl- cotransporter)

Question 21

Why is epithelia important?

Answer 21

Seperate compartments, produce fluids that are not isotonic

Question 22

What types of epithelia is there, and how do they differ?

Answer 22

Leaky: isoosmatic transport, large volumes
Tight: large gradients, water-tight