Calcium and Heart Function Flashcards
What is the average concentration of extracellular calcium?
2 mM
What is meant by the term excitation-contraction coupling?
Excitation is the action potential. The plateua phase of the action potential allows calcium in, so we get a coupling to contraction.
What are L-type calcium channels?
Long activity calcium channels
What are the two reasons why it is important for ventricular myocytes to have long plateau phases?
Calcium is needed in the cell for contraction; A longer phase means that we cannot restimulate the ventricular cell too quickly
What are the major types of calcium channels on the sarcolemma?
Voltage-gated, L-type, dihydropyridine receptors
What mechanism do calcium channels use to transport calcium into the cell?
Diffusion
What is verapamil’s mechanism and what is its physiologic effect?
Dihydropyridine antagonist; decreases contractility
What is the mechanism of isoproterenol? What is its effect on calcium?
beta-1 agonist; causes phosphorylation of the calcium channels and allows for calcium influx
What type of channels are ryanodine channels? How do they work?
Clacium induced calcium release (CICR) channels; Calcium influx from the ECF to the cytosol induces the opening of the channels allow calcium to flow out of the sarcoplasmic reticulum
What are the two different parts of the sarcoplasmic reticulum? Where are ryanodine receptors located on the SR?
Cisternal and longitudinal parts; RyRs on cisternal part
How does the sarcoplasmic reticulum reuptake calcium? What part of the sarcoplasmic reticulum accomplishes this?
Ca++-ATPase Pump; Longitudinal part
What inhibits the Ca++ ATPase Pump on the SR at normal resting HR?
Phospholamban
How is phospholamban regulated?
Protein kinase A (activated by SNS) phosphorylates phospholambin inhibiting its effect on the ATPase
How is inhibition of phospholamban consistent with the overall effect of SNS stimulation?
Inhibiting phospholambin means that there is increased activity of Ca-ATPase, which increases the rate of calcium uptake into the SR, allowing for faster relaxation rate
What are the Vmax and Km of the 2 types of Ca-ATPase relative to one another?
Sarcolemma Ca++ATPase pump has a lower Km for calcium but a lower Vmax than the sarcoplasmic reticular pump
True or false: the sarcolemma Ca++ATPase Pump during diastole?
True
What is the action of the Na+/Ca+ exchanger? What powers the exchange?
Moves 3 Na+ inside the cell and 1 Ca++ outside of the cell; powered by Na+ electrochemical gradient
What are the two mechanisms for stimulating stronger contractions?
Frank Starling mechanism and calcium movement
How does calcium movement within the sarcoplasmic reticulum affect contractility?
The calcium is uptaken into the longitudinal SR and is released from the cisternal SR and so the longer a time interval between contractions, the more calcium has time to get to the cisternal end, resulting in a bigger release of calcium and stronger contraction
What generates the Na+ gradient across the sarcolemma?
Na+/K+ ATPase
What is the effect of cardiac glycosides on Na+ and Ca++ levels?
Decreased Na+ gradient and increased cytosolic Ca++
What kind of compound is digitalis? How does it increase contractility?
A glycoside; Inhibition of Na+/K+ ATPase Pump diminshes the Na+ gradient, causing less Ca++ to be exported from the cell- making more Ca++ available in the cell to increase contraction
How does pulmonary edema develop as a result of a weaker heart?
As the heart weakens, it has lower contractility and must increase its preload (EDV) to maintain stroke volume. As EDV gets really big, EDP and LAP get high, causing an elevated pulmonary capillary pressure (PCP) which works as a filtration force. This causes poor diffusion of O2 and CO2 in the alveoli making it harder to breathe
What enzyme reverses SNS response?
Phosphodiesterase
What three proteins phosphorylated by PKA cause increased contractility and rate of relaxation? What is the effect of phosphorylation on each?
L-type voltage gated Ca++ channels (stimulation), Phospholambin (inhibition), Troponin (decreases Ca++ affinity)
How does phosphorylation of troponin increase the rate of relaxation?
Phosphorylation decreases its affinity for Ca++, allowing calcium to release from troponin faster
What is the only thing in the cardiovascular system that is set and monitored?
Blood Pressure
