Scientists have figured out how calcium channels the infinitesimal cell membrane pores that generate electrical signals by gating a charged-particle influx have solved a "needle in a haystack" problem.
The solution to the longstanding riddle is reported in the Nov. 24 advanced online edition of Nature by University of Washington and Howard Hughes Medical Institute investigators. Dr. Ning Zheng, a noted X-ray crystallographer, and Dr. William Catterall, a pioneer in ion channel research, were the senior researchers, and Dr. Lin Tang and Dr. Tamer Gamal El-Din headed the project.
The cardiac muscle cells of the heart face an extracellular fluid where the concentration of sodium ions is 70 times greater than that of calcium ions. Even though calcium and sodium ions are nearly identical in diameter, calcium channels preferentially pass the far-less-abundant calcium ions through them with astounding speed. Calcium ions gush through the voltage-gated calcium channels of cells at the rate of more than one million ions per second.
"How calcium channels are able to solve this fundamental biophysical problem has been a longstanding question in cell physiology," Catterall said. The answer is important to both science and medicine.
The speed and accuracy of these channels in selectively filtering the calcium ions is crucial to many biological activities in which cells cooperate, Catterall explained. Muscle contractions, including the rhythm of the heart, hormone secretion and nerve and brain impulses all depend on these particular channels' ability to pass calcium through and keep sodium at bay. Calcium channels are also the target of many medications for epilepsy, high blood pressure, heart disease and other serious conditions.
Sodium channels and calcium channels in animals both likely evolved from a single ancestral type of sodium channel in bacterial cells, and kept similar structures and functions, the re
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University of Washington