regulation of cardiac muscle contraction
DESCRIPTION
Regulation of cardiac muscle contraction. Graded contractions Effect of cardiac muscle stretching Channel activity during action potentials In myocardial contractile cells In autorhythmic pacemakers. Graded contraction. The amount of force varies with the number of cross-bridges formed - PowerPoint PPT PresentationTRANSCRIPT
Regulation of cardiac muscle contraction
• Graded contractions
• Effect of cardiac muscle stretching
• Channel activity during action potentials– In myocardial contractile cells– In autorhythmic pacemakers
Graded contraction
• The amount of force varies with the number of cross-bridges formed
• Low Ca++ few cross-bridges
• High Ca++ more cross-bridges
The effect of epinephrine and norepinephrine of contraction
• NE and E bind to beta 1 receptors on contractile myocardial cells
• The beta 1 receptor is coupled to a G protein
• Cyclic AMP is formed
The effect of epinephrine and norepinephrine of contraction
• cyclic AMP is formed
• 1. Voltage gated Ca++ channels are phosphorylated stay open longer more intracellular Ca++ stronger contractions
• 2. A regulatory protein, phospholamban, is phosphorylated increased activity on SR Ca++ ATPase contractions shorten duration
Effect of phospholamban on Ca++ release
• NE and E activityincrease phospholamban activity increase Ca++ ATPase activity on SRmore Ca++ is sequestered into the SRmore Ca++ is available for Ca++ release
during stimulationstronger force of contraction
Effect of NE and E on contraction
• Stronger, more frequent contractions
When myocardial cells elongate
• The amount of Ca++ entering the myocardial cells may increase
the force of contraction increases
Myocardial contractile cell action potentials
• Resting potential is stable -90 mV• Wave of depolarization through gap
junctions• Voltage gated Na+ channels open• Voltage gated K+ channels open• Slow voltage gated Ca++ channels open
and K+ channels close• Ca++ channels close and K+ channels
open
Long action potential
• Myocardial cell refractory period and contraction end simultaneously
Action potentials in myocardial autorhythmic cells
• The channels:– If channels allow passage of Na+ and K+
– Ca++ channels
Action potentials in myocardial autorhythmic cells
• Unstable resting membrane potential• Pacemaker potential• At a membrane potential of -60 mV Na+
enters through the If channels mb depolarizes Ca++ channels open Ca++ channels close K+ leaves
Modulation of autorhythmic cells
• NE (sympathetic) and E (adrenal hormone)
• Autorhythmic cells have beta1 receptors• Cyclic AMP levels increase• Properties of If and Ca++ channels altered• More rapid Na+ and Ca++ entry• Rapid action potential• Rapid contractions
Modulation of autorhythmic cells
• Parasympathetic, acetyl choline
• Muscarinic receptors
• K+ channels open mb hyperpolarizes cell less excitable
• Ca++ channel less likely to open slower depolarization cell is less excitable