Another long title. The whole thing is below.

Hubmed Page: Role of Cardiac ATP-Regulated Potassium Channels in Differential Responses of Endocardial and Epicardial Cells to Ischemia

This 8-page article quantifies in great detail the ATP sensitivity of ATP-regulated potassium channels, often referred to as I_K(ATP). As the article shows by many references, it’s known that the epicardium of the heart is more sensitive to lack of oxygen (and therefore metabolic energy in the form of adenosine triphosophate — ATP) than then endocardium of the heart. The authors of this study first measured currents from ATP-regulated potassium channels in the presence of CN^– (cyanide, which blocks the generation of ATP), and then more directly pulled off patches of cell membrane with ATP-regulated potassium channels, and tested them in the presence of varying concentrations of ATP. In both cases, action potentials (the way in which cardiac cells ‘fire’ to initiate contraction and signal each other) were shortened more in the epicardial patches than in those from the endocardium. The degree to which this shortening occurred and at what concentrations is well-documented in the article.
The results of this study are clear, well-presented, and extremely useful in modeling ischemia in the heart. It’s a long read, with a ton of experimental detail, but the results are worth slogging through all of that. This fundamental article on ATP-regulated potassium channels is a must-read for anyone wanting to study ischemia and infarction in the heart.

I had to cut the title a bit short, because it’s a long one.

Hubmed Page: What can nonlinear dynamics teach us about the development of ventricular tachycardia/ventricular fibrillation?

This short article (3 pages) describes in a very readable way how nonlinear dynamics may be applied to understand beat-to-beat alternans of action potential duration and amplitude. While the actual methods used are not written, the concept is well-conveyed. I’ve not yet had a course in nonlinear dynamics, so some of the terminology was a bit beyond my understanding. I don’t know anything about eigenmodes, for example.

After providing a brief background of nonlinear dynamics, the authors elaborate on how they used nonlinear dynamics to develop a realistic model of calcium cycling and alternans in the canine myocardium. All-in-all, it’s not a terribly informative paper. Like many articles that mention fibrillation and tachycardia, it comes up short of actually linking the found mechanisms to clinical application and human disease. It is, however, a nice introduction to the topic, and the references look promising. If you have an interest in cardiac arrhythmias, and aren’t very familiar with this sort of analysis, I recommend you read it over and consider further study of the topic.