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Receptor and Signaling > Calcium Signaling II > Flashcards

Calcium Signaling II Flashcards

1
Q

what are the two Ca binding domains

A

C2 domain and EF-hand domain

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2
Q

what is the structure of EF-hand domain

A

“helix-loop-helix” protein motif, with the loop specialized to
bind a metal ion

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3
Q

what part of the EF hand domain bind to Ca ion?

A

helix-loop

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4
Q

what are the two classes of EF-hand domain

A

Ca buffers and Ca sensors

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5
Q

__________ types of EF-hand domain does not alter protein and _____________ change protein conformation

A

Ca buffers

Ca Sensors

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6
Q

Give 3 examples of Ca buffer and 5 examples of Ca sensors

A

Ca2+ buffers
• Calbindin D-28k (6 EF-hands)
• Parvalbumin (3 EF-hands)
• Calretinin (6 EF-hands)

 Ca2+ sensors 
• Calmodulin (4 EF-hands)
• Troponin C (4 EF-hands)
• Calcineurin B (4 EF-hands)
• Calpain (5 ER-hands)
• S100 proteins (a large family)
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7
Q

where does Ca interact in the EF-hand domain ?

A

ca interacts with with O2 atom mainly of glutamate and aspartate side-chain
groups) in the loop

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8
Q

what does s100% mean

A

Soluble in 100% ammonium sulfate

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9
Q

what is calmodulin

A

A ubiquitous Ca2+-binding protein

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10
Q

what and how many Ca does one calmodulin bind to be activated

A

Each molecule of CaM cooperatively binds 4 Ca2+(4 EF-hand domains); all 4
sites must be occupied by Ca2+ for CaM function

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11
Q

does CaM have enzymatic activity?

A

CaM has no enzymatic activity, even when bound to 4 Ca2+ ions!!!

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12
Q

how does CaM function?

A

interaction with Ca2+/CaM à change
conformation of target protein (often
by relieving autoinhibition) à altered
target protein function

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13
Q

What is CaM-Kinase

A

A family of serine/threonine kinases that mediate many of the effects of Ca2+/CaM

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14
Q

what are the types of CaM-kinases

A
  1. Substrate-restricted: Responsible for phosphorylation of a specific substrate
  2. Multifunctional
    Broad substrate specificity
    CaM-kinase II (CaMKII) is the most prominent example
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15
Q

what are CaM-kinase II substrates

A

tyrosine hydroxylase
ion channels
CaM-kinase II

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16
Q

what factors increase Ca

A

Receptor complexes
that generate IP3
Membrane Ca2+
channels

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17
Q

what factors decrease Ca

A

Ca2+ pumps and
exchangers
Ca2+ buffers

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18
Q

what are membrane Ca channels

A

§ Located in the plasma membrane and in membranes delimiting organelles

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19
Q

Channel opening allows _____________movement of Ca2+ down______________

A

passive

electrochemical gradient.

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20
Q

what are the membrane potentials for plasma membrane and mitochondrial membrane

A

Plasma membrane is inside-negative (-70 mV)

Mitochondrial membrane is matrix-negative (-150 mV)

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21
Q

what is the Ca concentration for resting state for extracellular fluid, cytosol and ER?

A

EF: 2mM
cytosol: 100nM
ER: 300-800uM

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22
Q

what is the Ca concentration for stimulated state for extracellular fluid, cytosol and ER?

A

EF: 2mM
cytosol: 1000nM
ER: 100uM

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23
Q

How does Plasma membrane involved in Ca channels

A

Provide an avenue for sustained Ca2+ entry into the cell, allowing prolonged elevations
of Ca2+

Multiple types of Ca2+ channels

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24
Q

what are types of Ca channels

A

ligand-gated
voltage-gated
store-operated

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25
Q

Voltage gated ion channel has _______ pore forming ___________ subunit

A

4

pore-forming (a1) subunit

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26
Q

how many subunits does Voltage gated Ca Channel

A

4 accessory subunits

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27
Q

discuss structure of Voltage gated Ca channel a1 subunit

A

4 pore-forming domains (I-IV), each with 6 transmembrane

segments (S1-S6) connected by intracellular or extracellular loops

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28
Q

Nifedipine

A

specifically blocks Cav1 (L-type)

important antihypertensive agent

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29
Q

EGTA

A

avidly binds extracellular Ca2+ (calcium chelator)

blocks all responses dependent upon Ca2+ influx
regardless of the type of Ca2+ channel

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30
Q

a1 subunit pore loop confer to ______

A

Ca selectivity

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31
Q

a1 subunit Regulatory domain confer to _____________

A
  • EF-hand (Ca2+)
  • Ca2+/CaM
  • PKC
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32
Q

How does ER/SR membrane involved in Ca channels

A

Allows rapid Ca2+ mobilization from intracellular “stores”

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33
Q

ER/SR Ca channels are ________________ gated

what are the two types

A

ligand

two types
IP3 receptor
Ryanodine receptor

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34
Q

what are IP3 receptors

A

A ubiquitous ligand-gated ion channel in the ER or SR
membrane
homo- or hetero-tetramer

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35
Q

IP3 regulatory domain has

A

Ca binding
ATP binding
phosphorylation site

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36
Q

how many domains does IP3 has

A

Regulatory domain
IP3 binding domain
Channel domain

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37
Q

Ca2+ release via IP3Rs is a
primary signal to activate
processes in ______________
cells.

give examples

A

non-excitable cells

• Fertilization (oocytes)
• Proliferation (lymphocytes)
• Metabolism (hepatocytes)
• Secretion (salivary gland; 
pancreas)
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38
Q

IP3R activation usually triggers brief ______________

A

transients of Ca2+ release

39
Q

_________ responses generally involve repeated spikes/oscillations.

A

longer duration

40
Q

Oscillation frequency characteristically depends on the level of _____________

A

stimulus intensity.

41
Q

what are the three IP3R isoforms

A

IP3R1, IP3R2, IP3R3

42
Q

what is the point of the three IP3R isoforms

A

similar primary structures but different
physiological properties

allows cells to create IP3-dependent
[Ca2+]i signals with distinct spatial and
temporal characteristics to control many
cellular functions

43
Q

_____________ in the cytosol are required for channel opening (primary regulators)

A

IP3 and Ca2+

44
Q

Channel activation

A

↑[IP3]i à 4 IP3 molecules bind to the IP3R tetramer à conformation change
sensitizes Ca2+ binding site à Ca2+ binds à conformation change opens the pore à Ca2+ release into
cytosol.

45
Q

what are the secondary regulation of IP3R activity

A

Factors that tend to ↑IP3R activity
cytoplasmic nucleotides (ATP)
PKA-mediated phosphorylation
reactive oxygen species tumor suppressors

Factors that tend to ↓IP3R activity
PKG-mediated phosphorylation Protooncogenes
Very high [Ca2+]i (> 300 nM), likely through Ca/CaM

46
Q

Xestospongin C

A

membrane-permeable

sterically blocks Ca2+ pore

47
Q

Heparin

A

membrane impermeable

competes for IP3 binding

48
Q

Ryanodine receptor (RyR)

A

A ligand-gated ion channel in the ER/SR

membrane, structurally related to the IP3R

49
Q

The functional channel of Ryanodine receptor (RyR)

is a

A

homotetramer

50
Q

what are the isoforms Ryanodine receptor (RyR)

A

3 isoforms:
RyR1 (skeletal muscle)
RyR2 (cardiac muscle)
RyR3 (more ubiquitous)

51
Q

what is calsequestrin

A

a Ca2+-binding

protein

52
Q

________________ draw calsequestrin into a complex with the RyR

A

Junctin & triadin

53
Q

___________ maintains proper spacing between SR

and plasma membran

A

Junctophilin

54
Q

Ryanodine

A

a plant alkaloid

μM concentrations inhibit channel opening

55
Q

Caffeine

A

mM concentrations activate the RyR

56
Q 
Ca2+ release via RyRs and 
influx via VGCCs are 
primary signals for 
activating processes in 
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

give example

A
  • Contraction (muscle)
  • Insulin secretion (b cells)
  • Excitability (neurons)
57
Q

______________ is the primary activator of RyRs

A

Cytosolic Ca2+

58
Q

Source of the an increase in Ca is

A

Ca2+ channels in the
plasma membrane or in the ER/SR, even nearby
RyRs (resulting in a wave of RyR activation and
Ca2+ release from the ER/SR)

59
Q

In excitable cells, plasma membrane depolarization sensed by _______________ opening of RyRs via _____________ or _____________ mechanisms

A

voltage-gated Ca2+ channels
(VGCCs)

direct or indirect mechanisms

60
Q

direct mechanism of RyR is ____________ muscle and indirect mechanism is _______ muscle

A

skeletal

cardiac

61
Q

direct mechanism of RyR is through ________________ of plasma membrane VGCCs with
RyRs in SR membrane

A

Physical coupling

62
Q

Indirect mechanism of RyR is through _____________ positions RyRs in SR membrane close to
plasma membrane VGCCs

A

Junctophilin

63
Q

what is the role of Ca2+ pumps and exchangers

A

to remove Ca2+ from the cytosol

Keep [Ca2+]i low under resting conditions

Restore low [Ca2+]i after a Ca2+-dependent stimulus

Either extrude Ca2+ from the cell or sequester it into organelles

64
Q

what are the two types of Ca pumps

A

Plasma membrane Ca2+-ATPase (PMCA)

Sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA)

65
Q

what are the two types of Ca exchange

A

Na+/Ca2+ exchanger (NCX)

Na+/Ca2+/K+ exchanger (NCKX)

66
Q

PMCA Hydrolyzes __________ molecule to extrude _____________ Ca2+ from the cell against its electrochemical
gradient

A

1 ATP

1 Ca2

67
Q

PMCA has ____________ Ca affinity but _______ capacity

A

High affinity low capacity

68
Q

_____________ Provides the major route of Ca2+ extrusion at resting [Ca2+]i (~100 nM)

A

PMCA

69
Q

PMCA is Regulated primarily by________

A

Ca2+/CaM

70
Q

What is the similarity between PMCA and SERCA

A

A primary active transporter

High affinity & low capacity

71
Q

SERCA Hydrolyzes ___________ molecule to pump _________ into the SR/ER against its
concentration gradient

A

1 ATP

2Ca2+

72
Q

Thapsigargin

A

specific & potent

forms a dead-end complex

73
Q

Cyclopiazonic acid

A

competitive at the ATP

binding site

74
Q

how do we regulate SERCA

A

↑ [Ca2+]i à ↑ SERCA activity

Protein kinase A-dependent phosphorylation of
phospholamban (PLB) à ↑ SERCA activity

Inhibited by high [Ca2+] in the ER or SR lumen

75
Q

Ca2+-binding proteins in the lumen keep [Ca2+]ER/SR in the ________range

A

uM

76
Q

______________(in ER) and ___________(in SR) are high capacity, low affinity Ca2+ buffers
that can bind up to 50 Ca2+ per molecule

A

Calreticulin (in ER) and Calsequestrin (in SR)

77
Q

_______________ is a secondary active transport

A

NCX

78
Q

NCX relies on the inwardly-directed __________ to drive uphill extrusion
of _____________ from the cell.

A

3 Na+ electrochemical gradient t

2 Ca2+ from the cell

79
Q

why is NCX important when cytosolic Ca rise

A

Low Ca2+ affinity, but very high capacity

80
Q

NCX processes ______ cycles/sec Ca during influx

A

5000 cells/sec

81
Q

how is NCX regulated?

A

by Ca

[Ca2+]ià ↑ NCX activity

82
Q

NCX has ________ Ca binding domains?

A

2 Ca

83
Q

Refilling the Ca2+ store is called _______________

A

Capacitative Ca2+ influx

84
Q

↓ [Ca2+]SR/ER à activation of “X ________________ in the plasma
membrane à Ca2+ influx into a sub-plasmalemmal space

A

“Store-Operated Channels” (SOCs)

85
Q

EGTA

A

Ca2+ chelators that bind free Ca2+, thus preventing Ca2+-

dependent effects

86
Q

A23187, others

A

Ca2+ ionophores that let Ca2+ flow freely across cell

membranes

87
Q

Thapsigargin, Cyclopiazonic Acid

A

SERCA inhibitors that prevent Ca2+ reuptake into ER/SR

88
Q

Xestospongin

A

current best IP3R blocker

89
Q

Nifedipine (a dihydropyridine), others

A

blocks Ca2+ influx through

voltage-gated Ca2+ channels (DHPRs)

90
Q

Ryanodine (µM concentrations)

A

blocks RyRs

91
Q

Caffeine (mM concentrations)

A

activates RyR

92
Q

PMA (phorbol ester)

A

activates conventional & novel PKC isoforms

93
Q

Calphostin C

A

inhibits PKC

Receptor and Signaling (6 decks)

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