In the past month I've run across a couple different studies that have shed a little enlightenment on the role of calcium channels in physiology - the ion channels are getting a little love in the literature.
Calcium channels are proteins in cell membranes that activate signaling cascades in the cell when calcium ions activate them. Calcium plays important roles in many cell processes, from muscle movement to neurotransmitter release, and even sperm contain calcium channels.
In fact, recent research has indicated that these channels (called CatSper, because they are specific to the tail of the sperm) may solve the mystery of how sperm seek out an egg. These CatSper channels are activated by progesterone, which is produced by the egg after it's released from the ovaries. Two different research groups found that the motility of the sperm in mice is quickened by progesterone, and one found that the system involved in egg penetration is activated by this response.
Other researchers identified the calcium channels involved in the fight or flight response, the physiological response to acute stress. Calcium released by the muscle stores, which occurs to allow quick muscle movement for fight or flight, activates the receptors involved in blood pressure and cardiac regulation to trigger quicker reflexes.
Calcium channels are also linked to heart failure and cardiovascular conditions, with beta blockers and calcium channel blockers used as anti-hypertensive drugs. From movement to conception and defense, calcium channels are responsible for a lot of what we know about being alive.