L19 Decoding Ca2+ Signals

elementary calcium events stay…

• restricted/localised in space within the cell (5micrometer diameter)

• very restricted in time (200ms duration)

what happens that results in the visualisation of elementary calcium release events

release of calcium from a cluster of 10 IP3 receptors on the ER

what is the release of calcium from a cluster of 10 IP3 receptors on the ER due to the elementary calcium release event called

Ca2+ puff: IP3

Elementary calcium release events from RyRs are called a…

Ca2+ Spark

what are the Ca2+ puffs and sparks the forerunner to

a wave

the Ca2+ puffs and sparks are calcium signals…

in their own right

describe the hierarchical organisation of intracellular Ca2+ signalling

• fundamental event (low)

• elementary event (intermediate)

• global event (high)

low, intermediate, high stimulus intensity

what is the stimulus intensity of a global event

high

what is the stimulus intensity of an elementary event

intermediate

what is the stimulus intensity of a fundamental event

low

increasing stimulation intensity of a cell…

generates more IP3 so IP3 acts as a co-agonist at more IP3 receptors

• receptors behave as CICR channels and release Ca2+

• puff sites get larger as more IP3 receptors are recruited

what is the calcium release event called from one IP3 receptor (fundamental event)

Ca2+ blip

what is the calcium release event called from one RyR (fundamental event)

Ca2+ quark

what is the only way to visualise blips and quarks

activating very low levels of hormone/stimulus

Sometimes if the cell is between stimulus intensities (e.g. between intermediate and high) what occurs

an abortive wave

elementary release events are physiological signals…

in their own right

in all muscle cells what do you need to cause a contraction?

a global calcium wave

smooth muscle cells contain… in their plasma membrane

calcium activated potassium channels

if the cell has a calcium spark in the vicinity of a calcium activated potassium channel, what happens

the calcium spark will activate the calcium activated potassium channel

• potassium ions leave the cell down the conc gradient

• cell becomes more negative (potassium has a positive charge)

• cell hyperpolarises

what happens when a muscle cell hyperpolarises

favours muscle relaxation

Ca2+ can trigger the opposite physiological response in the same cell, depending on…

the type of calcium signal (e.g. spark or wave)

what does a Ca2+ spark trigger in the smooth muscle cell

relaxation

what does a global Ca2+ wave trigger in the smooth muscle cell

contraction

Intercellular Ca2+ waves in cilia of trachea take how many seconds

10

how is coordination of cilia on the trachea achieved

intercellular Ca2+ wave

what are trachea cilia connected to each other by

a gap junction

what does a gap junction mean

the two cytosols of cells are continuous

stimulating the cell generates the IP3 which can behave as CICR channels so you get a wave of calcium through the central cell, how does the wave propagate to other cells

• IP3 moves through the gap junction (sensitises IP3 receptors)

• Diffusion of Ca2+

both required to create an intercellular Ca2+ wave

give an example of decoding the Ca2+ signal into a physiological response

glycogen breakdown in the liver (glycogen metabolism- releasing glucose into the bloodstream)

give examples of intercellular Ca2+ waves

• monolayer of astrocytes and epithelial cells

• cilia in trachea

increasing hormone concentration will increase…

frequency of calcium spikes

Ca2+ binds to sensing protein called calmodulin which becomes activated and binds to… (decoding the Ca2+ signal into a physiological response)

calcium calmodulin (dependent) kinase II

when calcium calmodulin binds to calcium calmodulin kinase II, the kinase enzyme… (decoding the Ca2+ signal into a physiological response)

phosphorylates a target protein (phosphorylase kinase in the liver)

• using phosphate on ATP

the phorphorylate kinase in the liver phosphorylates… (decoding the Ca2+ signal into a physiological response)

phosphorylase

• using phosphate on ATP

when phosphorylase is active, it breaks down… (in the liver) (decoding the Ca2+ signal into a physiological response)

glycogen to glucose

what was the activating solution (to activate a Ca2+ spike)

• Ca2+

• calmodulin

• ATP (to measure phosphorylation)

what was the deactivating solution (deactivates the Ca2+ signal)

EGTA (chemical cage that binds Ca2+ ions -preventing activation of Ca cam kinase II)

100 pulses at 1 pulse/second (1Hz) meant the exp lasts 100s, how much activity of the kinase II enzyme was there

less than 10%

100 pulses at 4 pulse/second (4Hz), experiment lasts 25seconds, how much activity of the kinase II enzyme was there

increase in activity of kinase II enzyme (65%)

different frequencies of Ca2+ spikes can be decoded into…

different amounts of enzyme activity

kinase II enzyme spends time in its active state at the…

spike peak

increasing the frequency means the kinase II activity cant fully relax between calcium spikes so it…

spends much more time in its active configuration with the higher frequency of calcium spikes (able to breakdown more glycogen to glucose)