Lec 1 Resting Potentials

Question 1

What are the resting concentrations in and outside heart cell [K, Na, Ca]

Answer 1

inside: 140 K+, 10 Na+, 0.0001 Ca2+
outside: 5K+, 140 Na+, 2 Ca2+

Question 2

Is there higher Na in or out of cell? What about K?

Answer 2

higher Na out [10 in, 140 out]

higher K in [140 in, 5 out]

Question 3

What is function of Na-K ATPase? How much Na/K/ATP?

Answer 3

• moves 3 Na out
• moves 2 k in
• uses 1 ATP/step
• conformational change allows binding
• 3 Na and ATP bind inside, transfer P to pump, release Na out, bind 2K out, release P, release K in
• technically could be

Question 4

What is concentration of Ca in extracellular space? cytosol? SR?

Answer 4

• extracellular: 2 mM [10-3 M]
• cytosol: 100 nM [10-7 M]
• sarcoplasm reticulum: 1 mM [10-3 M]

Question 5

What is the function of Na-Ca exchanger [NCX]?

Answer 5

• 3 Na in, 1 Ca out of cell
• not a pump
• moves Ca uphill by exploiting Na gradient
• can work in reverse in some circumstances

Question 6

What is the function of SERCA?

Answer 6

• sarco-endoplasmic reticulum Ca2+ ATPase

- 2 Ca from cytosol into SR for 1 ATP

Question 7

What 2 things maintain the Ca gradient

Answer 7

• SERCA

- NCX

Question 8

What is PMCA? Is it important in cardiac cells?

Answer 8

• plasma membrane Ca ATPase moves Ca from cytosol out of cell
• not important in cardiac cells

Question 9

What are 3 ways ATP consumed in heart ell and their breakdown?

Answer 9

70% myosin ATPase [for muscle contraction]
20% NA-K ATPase
10% SERCA

Question 10

3 ways ions move across membranes

Answer 10

• ATP-consuming pumps: move ions uphill from low to high concentration
• ion channels: passive downhill movement, rapid
• co-transporters and counter-transporters: move one ion downhill and another uphill, no ATP

Question 11

What are 2 examples of ATP-consuming pumps?

Answer 11

• Na-K ATPase in cell membrane

- SERCA in SR membrane

Question 12

mechanisms of ion channels

Answer 12

• ions move downhill
• much greater/faster ion movement than pumps or transporters
• channel gating depends on voltage or binding ligands
• present in cellular and SR membranes

Question 13

What is the resting potential in cardiac myocyte

Answer 13

Vm = Vin - Vout = -85 mV

Question 14

What are the 2 drivers of Na/Ca ion movement:

Answer 14

• Diffusion: travels in direction of gradient

- Electric field: travels in direction of electric field [-mV means goes in, +mV means goes out]

Question 15

What does the RTlnC term of the nernst equation mean?

Answer 15

It describes diffusion – higher concentration leads to higher electrochemical potential

Question 16

What does zFV of the nernst equation mean?

Answer 16

it describes electrical effects – greater voltage leads to greater electrochemical potential for z>0 [positively charged things]

Question 17

What are the units of electrochemical potential?

Answer 17

J/mol

Question 18

What is assumed in the nernst potential

Answer 18

equilibrium: delta u = 0, Ui = Uo

Question 19

What is the electrochemical potential gradient equation of delta u

Answer 19

delta u = RT lnCi + zFVi - (RT ln Co + zFVo)

Question 20

What is the nernst equilibrium potential equation?

Answer 20

Equilibrium potential = Ex = Vi - Vo = RT/zF ln[Co/Ci]

Question 21

What is the value of RT/F?

Answer 21

25 mV

Question 22

What ion sets the resting voltage?

Answer 22

K+ – because it is the only ion that has lots of open channels permeable to it