L10 Myocardial E-C Coupling

Question 0

Functional role of T Tubule

Answer 0

transmits electrical activity to the cell’s interior; located at Z lines

Question 1

Functional role of Sarcolemma

Answer 1

propagates the AP down into the T tubule; Contains L-type Ca channels so controls Ca influx

Question 2

Functional role of SR

Answer 2

Site of Ca storage
Terminal Cisternae is where CICR occurs to initiate contraction
Longitudinal Cisternae is where SERCA functions to take Ca back into the cell for relaxation

Question 3

Functional role of Troponin C

Answer 3

Binds Ca when it’s available and moves the Tropomyosin/Troponin into the actin groove so actin/myosin can affiliate for contraction

Question 4

Troponin/Myosin in Heart

Answer 4

is the same as in skeletal muscle. Same contraction mechanisms

Question 5

Cellular mechanisms in E-C Coupling

Answer 5

1. Impulse from pacemaker cell conducts down cell and is carried into the cell by T Tubules
2. Depolarization causes slow inward Ca current via L-type Ca channels
3. Ca in the cell can now bind and open RyR channels
4. Ca released from SR and binds to Troponin-C
5. actin-myosin motion
6. SERCA takes Ca back into SR
7. Ca also removed via Na/Ca exchange and random Sarcolemma pump

Question 6

Cardiac vs. Skeletal: size

Answer 6

Cardiac: small

Skeletal: large

Question 7

Cardiac vs. Skeletal: innervation

Answer 7

Cardiac: all innervated in syncytium – coupled via gap connections

skeletal: all cells innervated separately

Question 8

Cardiac vs. Skeletal: electrical activation

Answer 8

Cardiac: cell-cell conduction

skeletal: NMJ using Ach

Question 9

Cardiac vs. Skeletal: contraction with Ca

Answer 9

Cardiac: uses CICR with Ryr

Skeletal: voltage dependent DHPR activates RyR
doesn’t require Ca, requires voltage to be depolarized

Question 10

Cardiac vs. Skeletal: contraction amplitude

Answer 10

Cardiac: larger amplitude = regulated by Ca influx in L-type and Ca content in SR

Skeletal: larger amplitude = frequency of APs summated and recruitment of more fibers

Question 11

Cardiac vs. Skeletal: metabolims

Answer 11

Cardiac: aerobic; requires O2 -> 35% mitochondria

Skeletal: anaerobic -> 2% mitochondria
never infarcts

Question 12

Factors that change contraction via changing Contractility: Catecholamines

Answer 12

NE, ie. - decreases time of relaxation & increases strength of contraction
positive inotropic effect - (definition of positive inotropic agent = something that increases CONTRACTILITY)

bind to B1 receptors, which make cAMP from ATP
cAMP activates PKA, which P’s *Ca channels (increases contraction strength by increasing influx), *phospholamban (enhances relaxation by enhancing SERCA activity), *Troponin-I, (enhances relaxation by inhibiting the binding of Ca to Troponin-C)

Question 13

Factors that change contraction via changing Contractility: Cardiac glycosides

Answer 13

ie: digitalis - increases strength of contraction ONLY
positive inotropic effects

block Na/K pump, which conserves ATP
increases Na concentration inside therefore lowering gradient for Na to come in.
Decreases Na/Ca exchange, so Ca builds up inside
SR Ca content goes up, increasing contraction strength

BUT – overloading SR with Ca can result in DADs

Question 14

Factors that change contraction via changing Contractility: Ca channel blockers

Answer 14

(Verapamil, Diltiazam, nifedipine) - increases Refractory period of slow response cells
negative inotropic effects on heart

Block Ca channels
Less Ca influx in heart
Less SR Ca content = decrease in contraction strength

good for treating arrhythmias bc is blocks slow Ca channel responses of AV node

Question 15

Force-Frequency relationship - all has to do with time allotted for Ca handling

Answer 15

Tells us that HR and rhythm affects contraction force

Fast HR = less time for filling and Ca extrusion therefore more Ca retained in SR and contractions become stronger
(positive staircase effect)

Slow HR = more time for Ca handling/extrusion, therefore less Ca retained in the SR and contractions become less strong
(negative staircase effect)

Question 16

Force-Frequency relationship - Premature beat

Answer 16

A premature beat would UNEXPECTEDLY allow less time for Ca handling, so less Ca is uptaken into the SR and less contraction occurs

Question 17

Force-Frequency relationship - Post extrasystolic potentiation (the beat after a premature beat)

Answer 17

This beat is extra strong because there is now a lot of time for Ca handling and a lot of Ca makes it back into the SR so the contraction is much stronger

Question 18

Sign of Atrial fibrillation

Answer 18

1) very fast pulse
2) pulse varies, force in each beat is different
3) irregular irregular beats