Calcium Metabolism

Question 1

intracellular concentration of calcium at rest and at contraction

Answer 1

rest: 10^-7 M
contraction: 10^-5 M or greater

Question 2

reasons for keeping calcium low

Answer 2

increased concentration inhibits dehydrogenases

-stimulates proteolytic enzymes

Question 3

sources of intracellular Ca++

Answer 3

RYR channel (SR) with contractions
DHP receptor (T-tubules of heart)

Question 4

mechanisms to keep cytosolic Ca++ low

Answer 4

Na+ Ca++ exchanger (in plasmalemma and mitochondria) powered by Na+ concentration gradient
-Ca++ ATPase pump (plamalemma, SR) requires ATP

Question 5

where is the Na+/Ca++ exchanger located?

Answer 5

in the plasmalemma and mitochondria

Question 6

where is the Ca++ ATPase pump located?

Answer 6

in the plasmalemma and the SR

Question 7

Ca++ ATPase pump

Answer 7

• requires ATP to keep Ca++ low
• 2 Ca++ per ATP
• concentration gradient: moves Ca++ up a steep concentration gradient (~2.5 mM, 10^-3 in blood)
• ~P-anion causes conformational change ~P from ATP
• rate compared to cation chanel: 1 sec, 10 x 10^8 through a Ca++ channel, but only 20 by a pump
• compensation: increase the # of pumps especially in the terminal cisternae (90% SR membrane are pumps)

Question 8

Ca++ binding proteins

Answer 8

troponin TnC
Calmodulin
Parvalbumin
Calsequestrin

Question 9

Troponin TnC

Answer 9

• 4 domains for binding Ca++

- muscle contraction

Question 10

calmodulin

Answer 10

4 domains for binding Ca++

target compounds

Question 11

parvalbumin

Answer 11

2 binding sites
increase concentration in type II fibers
sequesters Ca+ when concentrations increase

Question 12

calsequestrin

Answer 12

location: lumen of SR

binding capacity: increases, but low affinity (gives up calcium easily as with concentration)