cardiac cell electrophys

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Cardiac cells have multiphasic action potentials; e.g., _______ myocardial cells:: ventricular
Phase 0:: rapid upstroke
Phase 1: early partial repolarization
Phase 2: plateau; prolonged depolarization
Phase 3: final repolarization
Phase 4: interval between depolarizations (resting potential in cells which do not spontaneously depolarize)
There are two major types of action potentials the ________ & ________: fast response & slow response
in â€œFast responseâ€ APs the resting potential is approx. ______: - 90 mV
in â€œFast responseâ€ APs Phase 0 is ________: steep (fast).
â€œFast responseâ€ APs occurrence in ________, ______, & ________.: Normal ventricular and atrial myocardial cells.
& Normal Purkinje fibers.
In "Slow response⬝ cells the Resting potential is approx. ________: -60 mV.
In "Slow response⬝ cells Phase __ is slower; phase __ is absent & the plateau is less distinct, not as flat.: 0
1
In "Slow response⬝ cells amplitude is _________: diminished
In "Slow response⬝ cells ccurr in normal ___ node and ___ node cells & other myocardial cells under abnormal conditions.: SA
AV
Resting potential (in cardiac cells which do not spontaneously depolarize)is largely determined by distribution of ____ and ____ ions across the sarcolemma, and the permeabilities to these ions: K+
Na+
Vm = membrane potential * don't memorize: -61.5 log [K+]i+[Na/K] [Na+]i
_____________________________
[K+]o+[Na/K] [Na+]o

Pk=permeability of K
Pna=permeability of Na
Since the ratio (PNa/PK) is only about 0.01 during phase 4, the equation becomes essentially the Nernst equation for the potassium equilibrium potential (EK). Vm~Ek=: -61.5 log [K+]i/[K+]o
PNa is not zero, so Vm will always be a bit ________ than EK.: less negative
Since PK is relatively high, resting potential is very dependent upon ____.: [K+]o
Progressive increases in ____ result in progressive depolarization of resting cardiac cell membranes toward 0 mV.: [K+]o
Abnormal plasma _____ levels can have clinically significant effects on myocardial resting potentials.: [K+]
Since PNa is very low, _______ potential is relatively independent of [Na+]o.: resting
The normal concentration gradients would gradually decrease if the slight Na+ ______ and slight K+ _____ were uncompensated.: influx
efflux
Na+ and K+ transport is mediated by a membrane-bound, Na+, K+-activated _____.: ATPase
The pump is electrogenic: the ratio of Na+ to K+ pumped is about _:_ .: 3:2
Inhibition of the pump (e.g., by cardiac glycosides) results in partial _______ of the sarcolemma.: depolarization
_________ is opening of â€œfastâ€ channels for Na+ and increase in gNa (Na+ conductance).: Phase 0
Opening of fast channels is __________: the degree of opening increases as membrane potential approaches threshold voltage.: voltage dependent
When resting potential is normal, fast channels open rapidly and completely after _______. Action potential is large and rapidly rising.: stimulus
Partial depolarization _______ some fast channels. Action potential is smaller and more slowly rising.: inactivates
______ depolarization to threshold produces normal action potential whereas, ______ depolarization to threshold inactivates some fast channels. Action potential is smaller and slower rising, similar to the result when the resting potential becomes less n: Rapid
slow
Since depolarization is due to Na+ influx, [Na+]o affects the ______ of the action potential.: amplitude
[Na+]o does not affect the ______ potential significantly, due to low membrane permeability to Na+ in the resting cell.: resting
The recovery of the ability of fast channels to open is delayed until ______ of the fast response.: phase 3
In order for fast channels to open, Vm must approach ____(recovery is voltage dependent).: -90 mV
Full recovery requires several msec after return to resting potential (recovery is _____ dependent).: time
Fast channels begin to close as Vm approaches _____ during phase 0.: 0mV
______ in gK begins near the end of Phase 0 (K+ current (IK1) diminishes, but doesnâ€™t stop or reverse).: Decrease
______ in gCa begins during the upstroke (ICa).: Increase
______ is initiated when the closure of fast channels is complete.: Phase 1
During phase I, a transient, small efflux of __ ions contributes (Ito). Small influx of ___ ions may contribute.: K+
Cl-
"Slow⬝ channels carry primarily ___ ions.: Ca2+
"Slow⬝ Ca2+ channels (L-type, ICa) ____ to open during Phase 0.: begin
Calcium conductance, gCa increases as a result of their opening, resulting in a slow ______ current.: inward
Entering Ca2+ triggers release of more Ca2+ by _________.: sarcoplasmic reticulum
Slow channel opening is not affected by less _____ resting potentials as much as are fast sodium channels.: negative
Ca2+ influx is increased by ___________.: catecholamines
Certain ______ block slow Ca2+ channels (e.g., verapamil, nifedipine).: drugs
In phase 2, ________ is lower than Phase 4, but not zero.: K+ conductance (gK)
in phase 2, a small_____ K+ current balances the Ca2+ _______ , prolonging the plateau at about 0 mV.: outward (efflux)
influx
During phase 3, gK increases, allowing _______ to increase (repolarizing effect, IKr).: K+ efflux
During phase 3, ______ channels close, and gCa decreases; Ca2+ influx is shut off.: Slow
During phase 3, Recovery of ability of ____ channels to open occurs (see above).: fast
In cells with slow responses, fast channels are probably always ______ .: inactivated
Fast responses in fast response cells can be ______ to slow responses by pharmacologically blocking the fast channels (e.g., with tetrodotoxin).: converted
_____ does not affect the amplitude of a slow response action potential.: [Na+]o
Depolarization of phase 0 of a slow response is due to influx of ___ ions through slow _____channels: Ca2+
Ca2+
Depolarization of phase 0 of a slow response cannot be blocked by tetrodotoxin, but can be blocked by ____ channel blockers.: Ca2+
During depolarization of phase 0 of a slow response, Action potential amplitude is directly dependent upon ____.: [Ca2+]o
Conduction velocity is directly proportional to __________and __________: action potential amplitude
rate of depolarization.
Conduction velocity decreases when ________ becomes less negative (via the effects of resting potential on action potential amplitude and rate of depolarization).: resting potential
Since slow response action potentials are smaller and slower in depolarization rate, they are conducted slower than fast responses. Slow responses are also more easily _______.: blocked
_______ slow responses/unit time can be conducted compared to fast responses.: Fewer
Influences which change cardiac conduction velocity are called ________ influences.: dromotropic
During the __________vno propagated depolarizations are possible: effective refractory period (ERP)
Effective refractory period (ERP)lasts from _______ to _______: From beginning of phase 0 to middle of phase 3 (Vm ~ -50mV).
By the end of ERP, some ____ channels can reopen.: fast
During the _________ strong stimuli can result in propagated action potentials.: relative refractory period (RRP)
Duringt the relative refractory period (RRP),the number of fast channels able to reopen depends upon ___: Vm (voltage membrane)
During slow response, ERP may extend beyond phase ___.: 3
During slow response, RRP extends into phase ___: 4
Slow response, significantly prolongs recovery of ______.: excitability
During slow response, conduction velocity is proportional to level of _________.: excitability
Refractory period duration (and action potential duration) decrease as heart rate ______ (interval-duration relationship).: increases
Pacemaker Cells of the SA Node have several characteristics in common with the slow response: 1. Resting potential is less ________ than ventricular cells. 2. Phase 0 is relatively ____ . 3. A distinct ______is not seen. 4. Phase 3 is: negative
slow
plateau
slow
Ca2+
Spontaneous phase 4 depolarization is called the ________ .: pacemaker potential
_____________ results from unstable membrane ionic permeabilities and conductances.: Spontaneous phase 4 depolarization
a gradual increase in slow ___ influx begins during phase 3.: Na+
during spontaneous phase 4 depolarization, A slow ____ of Ca2+ begins in phase 4 (T-type channels and possibly a contribution by L-type channels also, ICa).: influx
during spontaneous phase 4 depolarization, ______ of K+ (IK1) gradually decreases throughout phase 4.: efflux
When pacemaker potential reaches the threshold voltage, an action potential occurs. Phase 0 results mainly from ____ channels.: Ca++
Rate of pacemaker potential depolarization and action potential amplitude are decreased by: a. Decreased external ___ concentration. b. ____ channel blocking agents.: Ca2+
Ca2+
Mechanisms which can change heart rate by changing SA node depolarization rate: 1. Change the rate of phase __ depolarization 2. Change the ______ voltage. 3. Change the _______ of membrane potential at the end of phase 3: 4

threshold

negativity
Influences which change heart rate are called ___________ .: chronotropic influences
Major Types of Ion Channels in Cardiac Cell Membranes: (give type & role) Fast Na+ (INa): Voltage-gated

Opening results in Phase 0 of fast response cells.
Slow Na+ (If): Voltage-gated &
Ligand-gated

Contribute to Phase 4 of pacemaker cells.
L-type Ca++ (ICa): Voltage-gated

Long-lasting, slow inward current during Phase 2 of fast response cells and Phases 4 and 0 of slow response and pacemaker cells.
T-type Ca++ (ICa): Voltage-gated

Channel opening is transient. Contribute to Phase 4 of pacemaker cells.
Inward rectifier K+ (IK1): Voltage-gated

Open channels are major contributors to Phase 4 potential. Depolarizations close them. Contribute to Phases 2 & 3 of fast response cells. Slow closure contributes to Phase 4 depolarization of pacemaker cells.
Transient outward K+ (Ito): Voltage-gated

Contribute to Phase 1, of fast response cells., also Phases 2 & 3 to some extent.
Delayed rectifier K+ (IKr): Voltage-gated

Opening results in Phase 3 repolarization. Also contribute to lesser extent to Phases 2 & 4.
ATP-sensitive K+ (IK, ATP): Ligand-gated

ATP inhibits opening. Reduced ATP results in greater opening, e.g., during hypoxia.
ACh-activated K+ (IK, ACh): Ligand-gated

ACh opens channel via Gi protein. Occurs with increased vagal activation

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Number of cards 93