Question

You are studying a cell from the heart but were not given information about where in the heart the cell came from. As you observe action potentials from this particular cell, you notice a few things: 1) the duration of the action potential is around 300ms, and 2) there is not a steady resting potential. If you were able to isolate ionic currents in this cell, what would you find?

1) Fast Na⁺ current, T-type and L-type calcium current, and rectifying K⁺ current
2) Fast Na⁺ current, L-type calcium current, and Kr/Ks
3) Funny Na⁺ current, Ito current, L-type calcium current, and Kr/Ks current
4) Funny Na⁺ current, T-type and L-type calcium current, and rectifying K⁺ current

Answer 1

The heart cell with a 300ms action potential duration and no steady resting potential is indicative of a cardiac contractile cell. It likely exhibits a fast Na+ current, L-type calcium current, and Kr/Ks current.

Step-by-step explanation:

The duration and characteristics of the action potential suggest that the cell is a cardiac contractile cell. Observing a duration of around 300ms for the action potential and the absence of a steady resting potential indicate that the ionic currents likely to be observed would include a fast Na+ current, L-type calcium current, and rectifying K+ current. These currents are consistent with contractile cells of the heart, which have longer action potentials due to a prolonged influx of calcium and exhibit a plateau phase, unlike conductive cells, which have a rather steady prepotential due to a slow influx of Na+ and lack the plateau phase.

The correct ionic currents you would expect to find in this heart cell would be option 2) Fast Na+ current, L-type calcium current, and Kr/Ks since these are indicative of contractile cells with long action potentials and no steady resting potential. This is due to the rapid influx of Na+, followed by calcium sustaining the plateau phase, and then potassium ions allowing repolarization.