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BS12001 > Lecture 7 > Flashcards

Lecture 7 Flashcards

1
Q

What is chloriNE?

A

An element/atom and a member of the halide series.

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2
Q

What are the two isotopes of chlorine?

A

Two isotopes with atomic mass of either 35 (35Cl) or 37 (37Cl) with 17 and 20 neutron respectively

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3
Q

What is the mean atomic mass and why?

A

35.5, it occurs because the isotopic composition (mole fraction) is about 75% 35Cl and 25% 37Cl

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4
Q

What is the most commonly used radioisotope?

A

36Cl, a predominantly Beta-emitter

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5
Q

What is ChloriDE?

A

A negatively charge ion (anion) formed when the third shell of chlorine (a gas) accepts and electron. It is sorrounded by hydration shells.

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6
Q

Why is partial dehydration of chloride important?

A

Partial dehydration of chloride is required for translocation and conduction of the ion by transporters and ion channels.

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7
Q

What is the normal plasma concentration of Cl-?

A

95-110mM (or mEq/L)

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8
Q

What is hypochloraemia?

A

Condition in which plasma concentration of Cl- is below 95mM.

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9
Q

What is hyperchloraemai?

A

Condition in which plasma membrane concentration of chloride is above 110mM.

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10
Q

What is the ICF concentration of Cl-?

A

It varies widely (5-40mM) between cell types and it is regulated by numerous transporters and ion channels.

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11
Q

What dictates the direction of flow of Cl- by facilitated diffusion?

A

The direction of movement is dictated by the relationship between the resting membrane potential and the equilibrium potential for Cl- and it is called the driving force.

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12
Q

What happen if ECl is negative to Vm?

A

The driving force is positive and Cl- moves into the cell (electrophisiologically and outward movement)

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13
Q

What happens if ECl is positive to Vm?

A

The driving force is negative and Cl- moves out of the cell (electrophisiologically an indward movement)

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14
Q

What are the six families of chloride channels?

A
  • ClCs
  • Cystic Fibrosis Transmembrane conductance regulator (CFTR)
  • Calcium-activated chloride channels (CaCC)
  • Volume-regulated chloride channles (VRAC)
  • Maxi-chloride channel
  • Ligand-gated ion channels (GABAA and glycine receptors)
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15
Q

Name all the members of ClCs:

A

Ion channels: ClC 1, ClC2, ClC-Ka/barttin, ClC-Kb/barrtin.

Cl-/H+ antiporters: ClC 3, 4, 5, 6 and 7/Ostm1

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16
Q

Name all the members of Calcium-activated chloride channels:

A

Anoctamin1

Anoctamin2

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17
Q

Describe ligand-gated ion channels:

A

Pentameric complexes of numerous subunit classes.

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18
Q

What are the two functional categories in which ClCs are divided?

A

1) Anion channels expressed in the plasma membrane

2) Cl-/H+ exchangers expressed in the membranes of intracellular organelles.

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19
Q

What is electroplax?

A

Is a “battery” of modified musclle cells capable of generating a very high voltage pulse if the fish is disturbed.

20
Q

What did experiments on myotonic goats in 1939 shown?

A

That muscle hyperexcitability is unaffected by denervation of the muscle, or by curare, hence the disease is that of muscle, not its motor supply.

21
Q

What did experiments conducted in 1939 shown?

A

Experiments show local intramuscolar infusion of KCl but not NaCl cause prolonged electrical discharges and contractile activity in myotonic, but not normal, muscle, hence muscle depolarization is the trigger.

22
Q

What did Katz and Ling and Gerrard shown in 1949?

A

That 80% of the resting membrane conductance (Gm) of skeletal muscle is due to a chloride conductance (GCl).

23
Q

What did Bryant estabilieshed in 1966 and 1974?

A

Using 36Cl- efflux from myotonic muscle of goats and electrophysiological experiments from patients, they estabilished that the disease is due to a drastically reduced Gcl of skeletal muscle fibers.

24
Q

What did Miller and colleagues characterised in 1979-1982?

A

They characterised an anion conductance in membranes from Torped electroplax by isolating electroplax vesicles. The SUVs fuse into a large liposome amenable to single channel recording techniques.

25
Q

How does the patch-clamp configuration used by Miller works?

A

Cl- flows through the channel from the bathing medium to the pipette driven by a positive voltage applied to the pipette (equivalent of a negative membrane potential)

26
Q

Describe the characteristics of a single channel record at Vm of -150mV in the presence of a high concentration (500mM) of Cl-.

A

You can note a closed state (D) and two open states (M and U) and that the single channel current in U state is exactly double that of M state.

27
Q

List the corresponding conductances of the three states (D, M, U)

A

D= 0pS
M=14 pS
U= 28 pS

28
Q

What are the two properties correlated with a membrane becoming more negative?

A

1) The probability of the channel being in the open (M and U) states increases at the expense of less time in the closed state (D).
2) The single channel current amplitudes increase linearly with the driving force upn the chloride ion (following Ohm’s law)

29
Q

What are the three conclusion reached by Miller et al.?

A

1) The anion channel is open at resting membrane potential but with opening probability increasing further with membrane depolarization.
2) The channel occupies three conductances states
3) the intermediate state (M) is exactly half of the maximum conductance state (U).

30
Q

What are the three conductances states occupied by ClC0?

A

1) Zero conductance (closed/inactivated) (D,I)
2) an intermediate conductance state (M)
3) a maximal conductance state (U).

31
Q

How did Miller interpreted his results?

A

The anion channel contains two identical conduction pathways, termed protopores.
The protopore operate (gate) independently during period of burst.
A likely dimeric structure with each subunit contributing a pore to an overall double-barrelled channel.

32
Q

Describe ClC proteins structure?

A

ClC are heterodimers, each with a separate Cl- conduction pathway.

33
Q

What does each protomer consists of?

A

18 helical domains (A-R) most of which do not cross the membrane and which are remarkably tilted.
2 intracellular cystathionine-β-synthase (CBS) domains.

34
Q

What do helices D, F, N and R do in the 3D structure of ClC?

A

They contribute to the Cl- conduction pathways.

35
Q

What do helices H, I, P and Q do in the 3D structure of ClC?

A

They are part of the interface between the two protomers.

36
Q

What does helix R do in the 3D structure of ClC?

A

Helix R connects the transmembrane element of the structure to the intracellular domain.

37
Q

Name the three anionic binding sites formed by each ClC protomer:

A

Sex
Scen
Sin

38
Q

Describe Sex, Scen Sin anionin binding sites:

A

Sex and Sin are exposed to extra and intracellular solutions respectively but Scen is cut off from water below by a constriction provided by the side chains of SerCen and TyrCen and above by a conserved glutamate residue, Gluex.

39
Q

What does the deprotonated side chain of Gluex do?

A

It can alternatively occupy Sex or Scen and competes with Cl- ion for binding.

40
Q

What happens if Gluex is occupy Scen?

A

The channel is non conducting.

41
Q

What happens in case of a mutation of Gluex to glutamine?

A

It mimick protonation of the Gluex side chain allowing the binding of Cl- ion, the channel is conducting.

42
Q

What hapens if Gluex is occupying Scen?

A

The channel is non-conducting.

43
Q

What condition is necessary for ClC-1 to conduct?

A

All Cl- binding (co-ordination) sites must be occupied by Cl- ions.

44
Q

What happens when Gluex is pronotaned?

A

Gluex moves out of the conduction pathway allowing Cl- ions to bind simultaneously to all three binding sites and the channel is conducting.

45
Q

What are two factors that faciliate opening of the fast gates of ClC-1?

A

Extracellular Cl- (competes with Gluex for binding)

Low extracellular pH (promotes the protonated species of Gluex)

BS12001 (4 decks)

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