Biology 304
Cardiac Muscle Lab

Cardiac muscle has some similarities to smooth muscle, and other similarities to skeletal muscle. There are two distinct types of action potential, and you should understand these, especially in light of the tested ions. In describing the effect of an agent on the heart beat, remember to include a description of both the heart rate and the contraction strength. The tracing below is a typical one showing both atrial and ventricular contractions. However, there are two atria...why doesn't the second atrial contraction show up?

The chart speed is 0.1 cm/s throughout.

Ionic Tests

How can you use the two cardiac action potentials to explain the following results?

Sodium - generally gives rise to an increased heart rate...why?

Potassium

Calcium What is the source of calcium for the heart cells?

Pharmacological Tests

Compare the results here with what you found in the smooth muscle labs.

Epinephrine     Propranolol

Acetylcholine

Acetylcholine followed by Atropine - the ACh effect is an extreme one.

This is a more typical one:

Eserine and Insecticide both showed effects similar to ACh. Why?

Eserine:

Temperature Effects

Series of temperature experiments can be found at this page.

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Thanks to all who contributed their data!

R.F. Lauff Department of Biology St. Francis Xavier University

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