cardiac myocyte Flashcards
skeletal muscle inducing contraction mechanism
skeletal muscle-
AP ->
DHP receptors cause Ca2+ release from SR = contraction
cardiac muscle inducing contraction mechanism
cardiac muscle-
AP ->
opens L-type Ca2+ channels ->
Ca2+ influx into cell causes Ca2+ release from SR = contraction
can a skeletal muscle reach tetanus
YES
can a cardiac muscle reach tetanus
NO
skeletal muscle AP duration & contraction duration
AP = 2.5 ms
contraction = 75 ms
cardiac muscle AP duration & contraction duration
AP = 200-300 ms
contraction = 300 ms
draw out cardiac excitation-contraction coupling
define inotropy
the amount of tension a myocyte can produce at any resting myocyte (and sarcomere) length
what are positive inotropic effects caused by (in general)
a signaling molecule that increases contractility by increasing cytoplasmic Ca2+ concentration
(increase cytoplasmic [Ca2+] = increase contraction strength)
what are negative inotropic effects caused by (in general)
a signaling molecule that decreases contractility by decreasing cytoplasmic Ca2+ concentration
(decrease cytoplasmic [Ca2+] = decrease contraction strength)
what is the Bowditch Effect
stepwise increase in HR
stepwise increase in contractility (due to increase in cytoplasmic [Ca2+])
beta-blockers (aka beta1 antagonists) are what kind of inotrope
negative inotrope
sympathetic mechanism to increase cytoplasmic [Ca2+] to increase contractility
beta-blockers (aka beta1 antagonists) mechanism & their drug name
prevent norepi from binding to beta1 receptors
->
inhibits cAMP from increasing contractility
end in -olol (metropolol, atenolol, acebutolol)
beta1 agonists are what kind of inotrope
positive inotrope
digitalis (a cardiac glycoside) is what kind of inotrope
positive inotrope
beta1 agonists mechanism & their drug name
stimulates beta1 receptors
->
increases contractility
end in -ine (dobutamine, norepinephrine, epinephrine, dopamine)
digitalis mechanism
inhibits Na+/K+ ATPase
decreases Na+/Ca2+ exchange (decreases Ca2+ leaving cell)
=
increases cytoplasm [Ca2+]
=
increases Ca2+ uptake by SR
=
increases contractility
increase in sarcomere length
_____ in tension generation
increase
(up to peak that sarcomere allows & then decreases)
why does increasing sarcomere length increase tension?
-increased overlap of actin & myosin
-length-dependent increased sensitivity of troponin C to Ca2+
-stretch-activated plasma membrane Ca2+ channels
define the Frank-Starling relationship
changes in inotropy directly change the curve & slope of lenth-tension relationship
Frank-Starling relationship with increased inotropy
shift up / to the left
+
higher slope
Frank-Starling relationship with decreased inotropy
shift down / to the right
+
lower slope
cardiac muscle fiber type
striated, branched, uninucleated
skeletal muscle fiber type
striated, tubular, multinucleated
in cardiac muscle:
2 mechanisms to lower cytosolic Ca2+ to end contraction
SERCA sequesters Ca2+ & brings it to SR
Na+/Ca2+ exchanger lowers cytosolic Ca2+ (pushes more Ca2+ out)
