Exercise 6: Cardiovascular Physiology: Activity 5: Examining the Effects of Various Ions on Heart Rate Lab Report Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. Which organelle in the cardiac muscle cell stores calcium? You correctly answered: b. sarcoplasmic reticulum 2. Verapamil is a calcium-channel blocker. Its effects could be described as You correctly answered: d. negative chronotropic and negative inotropic. 3. When the cardiac muscle cell is at rest, where is most of the potassium found? You correctly answered: c. in the cytosol 4. Resting cardiac muscle cells are most permeable to You correctly answered: b. potassium.
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Experiment Results Predict Question: Predict Question 1: Because calcium-channel blockers are negative chronotropic and negative inotropic, what effect do you think increasing the concentration of calcium will have on heart rate? Your answer : a. positive chronotropic, positive inotropic Predict Question 2: Excess potassium outside of the cardiac cell decreases the resting potential of the plasma membrane, thus decreasing the force of contraction. What effect (if any) do you think it will initially have on heart rate? Your answer : b. decrease heart rate Stop & Think Questions: Where in the cardiac muscle cell is most of the sodium normally found? You correctly answered: a. outside of the cell Experiment Data: Solution ---Calcium Sodium Potassium Heart Rate 59 69 34 then erratic 28 then erratic
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Post-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. The addition of most of the ions resulted in You correctly answered: c. an erratic heart rate. 2. The effect of potassium on the heart is You correctly answered: b. negative chronotropic, negative inotropic. 3. The ion that had the most pronounced effect on heart rate was You correctly answered: c. potassium. 4. Ectopic pacemakers can be caused by excessive leakage of potassium into cardiac cells, resulting in pacemakers appearing in abnormal locations in the heart muscle. This hyperkalemia (excess potassium) decreases the resting potential of the cardiac muscle cell. What effect do you think this would have on the force of contraction? You correctly answered: d. decrease, negative inotropic
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Review Sheet Results 1. Describe the effect that increasing the calcium ions had on the heart in this activity. How well did the results compare with your prediction? Your answer: Calcium ions increased the heart rate from 59 to 69 in this experiment. This was a positive chronotropic and picitive inotropic action. Which is the effect that increases heart rate. 2. Describe the effect that increasing the potassium ions initially had on the heart in this activity. Relate this to the resting membrane potential of the cardiac muscle cell. How well did the results compare with your prediction? Your answer: Increasing extracellular potassium levels initially resulted in depolarization of the membrane potentials of cells causing opening of some voltage-gated sodium channels, (not enough to generate an action potential) leading to a decreased heart-rate. My prediction of a decreased heart rate was correct.
3. Describe how calcium channel blockers are used to treat patients and why? Your answer: Calcium channel blockers used to reduce the force of heart contraction decreasing blood pressure. Calcium channel blockers reduce the amount of calcium that flows into smooth muscle which in turn lowers vasomotor tone and decreases peripheral resistance.
