You're a high school student? Have you done any basic science research so far? It's a lot different being in a lab and doing research than reading about being in a lab. How have you decided that you're interested in pursuing a research-heavy career?
Regarding reading journals, there really isn't anything you can read that would help you become a better MD/PhD applicant. I suggest working in a research lab during college to get experience and focus on reading articles related to your line of research. Have a good GPA, study hard, (hopefully) do well on the MCAT, and be able to discuss your research at interviews; pretty much like any other med school applicant.
If you're interested in reading for reading's sake, I'd suggest taking at look at some review articles in NEJM related to diseases you're interested in.