calcium-channel blocker, any of a class of drugs used in treating hypertension, angina pectoris, and certain arrhythmias. They prevent the calcium ions needed for muscle contraction from entering the cells of smooth and cardiac muscle. This causes blood vessel walls to relax and blood to flow more freely to the heart, lowering blood pressure and relieving anginal pain. Some calcium-channel blockers, such as Procardia (nifedipine), slow the electrical impulses that run through heart muscle, thus regulating arrhythmias. Cardizem (diltiazem) is a common calcium-channel blocker.

Saint George's Channel, strait, c.100 mi (160 km) long and 50 to 95 mi (80-153 km) wide, linking the Atlantic Ocean and the Irish Sea. It separates SE Ireland from Wales.

North Channel, strait, c.75 mi (120 km) long, between Northern Ireland and Scotland, connecting the Irish Sea with the Atlantic Ocean. It is 13 mi (21 km) across at its narrowest point.

English Channel, Fr. La Manche [the sleeve], arm of the Atlantic Ocean, c.350 (560 km) long, between France and Great Britain. It is 112 mi (180 km) wide at its west entrance, between Land's End, England, and Ushant, France. Its greatest width, c.150 mi (240 km) is between Lyme Bay and the Gulf of St.-Malo; at the east, between Dover and Cape Gris-Nez, it is 21 mi (34 km) wide. The Strait of Dover connects the Channel with the North Sea. Principal islands are the Isle of Wight and the Channel Islands. The principal Channel ports are Plymouth, Southampton, Portsmouth, and Dover (in England) and Cherbourg, Le Havre, Dieppe, and Calais (in France). Noted resorts include Deauville, France, and Brighton, England. A train-ferry service to carry passengers and freight between Paris and London was opened between Dover and Dunkirk in 1936. There are other ferry and hovercraft links, as well as the link under the Channel via the Channel Tunnel, opened in 1994. In 1785, J. P. Blanchard and Dr. John Jeffries crossed the Channel by balloon; the first person to swim across was Matthew Webb (1875); and the first airplane crossing was made by Blériot in 1909.

Channel Tunnel, popularly called the "Chunnel," a three-tunnel railroad connection running under the English Channel, connecting Folkestone, England, and Calais, France. The tunnels are 31 mi (50 km) long. There are two rail tunnels, each 25 ft (7.6 m) in diameter, and a central tunnel, 16 ft (4.8 m) in diameter, that is used for maintenance and ventilation. The depth of the tunnels below the seabed averages about 150 ft (45 m). The project is a joint English and French venture, with a 55-year concession granted to Eurotunnel, a private company, and is the centerpiece of a high-speed rail link between London and Paris. The project began with the signing of the Channel Tunnel Treaty between France and Britain in 1986; passenger service began in 1994. A higher than expected cost of digging the tunnels and lower than predicted tunnel traffic levels left Eurotunnel with huge debts, the repayment of which strained the finances of the company, threatened the company with insolvency, and led a French court to grant (2006) Eurotunnel creditor protection while the company reorganized (as Groupe Eurotunnel in 2007) and restructured its debt.

Channel Islands National Park: see Santa Barbara Islands; National Parks and Monuments (table).

Channel Islands, archipelago (2005 est. pop. 156,000), 75 sq mi (194 sq km), 10 mi (16 km) off the coast of Normandy, France, in the English Channel. The main islands are Jersey, Guernsey, Alderney, and Sark, and there are several smaller islands, including Herm, Jethou, and Lithou; all the islands are dependencies of the British crown. The inhabitants have traditionally been mostly of Norman descent, but on Alderney the stock is mainly English. In recent years many Britons have moved here, attracted by the favorable tax rates and the pleasant island atmosphere. Both French and English are the official languages. In addition, a Norman patois and Norman customs are still maintained by many of the natives.

The mild and sunny climate (35-40 in./89-102 cm rainfall a year) and the fertile soil have made the islands chiefly agricultural. Large quantities of vegetables, fruits, and flowers are shipped to English markets. Dairying is the chief occupation of the islanders. The famous Jersey and Guernsey breeds of cattle are kept pure by local laws. The islands are a favorite resort of tourists and vacationers. The chief ports are St. Helier (Jersey) and St. Peter Port (Guernsey).

The islands are divided into two administrative bailiwicks, one of which, Jersey, has more than half the total population. The other, Guernsey, includes all the islands except Jersey. Each bailiwick has its own lieutenant governor appointed by the crown, its own chief magistrate and legislature, and its own judicature.

Christianization took place in the 6th cent., largely through the efforts of St. Helier and St. Sampson. In the 10th cent. the islands became possessions of the duke of Normandy. At the Norman conquest they were joined to the English crown; they remained under the control of King John and England in 1204 when Philip II of France confiscated the duchy of Normandy. The French attempted unsuccessfully to reestablish control in the 14th cent. and later. In World War II, after the evacuation of some 10,000 military and civilian personnel, the islands were occupied (1940) by German forces.

Bristol Channel, inlet of the Atlantic Ocean, c.85 mi (140 km) long and from 5 to 50 mi (8.1-80 km) wide, stretching westward from the mouth of the River Severn and separating Wales from SW England. Its chief bays are Carmarthen and Swansea in Wales and Barnstaple (or Bideford) and Bridgwater in England. Many cities are on or near the channel; among the largest are Bristol, Newport, Cardiff, and Swansea. Along the coast of S Wales is a great concentration of economic activity, and Bristol Channel serves as a major shipping corridor. Milford Haven, a major oil-importing center, has a harbor that can accommodate large modern tankers.

or stream channel

Any long, narrow, sloping depression on land that had been shaped by flowing water. Streambeds can range in width from a few feet for a brook to several thousand feet for the largest rivers. The channel may or may not contain flowing water at any given time; some carry water only occasionally. Streambeds may be cut in bedrock or through sand, clay, silt, or other unconsolidated materials.

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Wide passage between the Irish Sea and the northern Atlantic Ocean. It extends for 100 mi (160 km) and has a minimum width of 47 mi (76 km) between Carnsore Point, Ireland, and St. David's Head, Wales. The name derives from the legend of St. George, in which he traveled to England by sea.

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or the Channel French La Manche (“The Sleeve”)

Strait between southern England and northern France. It connects the Atlantic Ocean with the North Sea through the Strait of Dover. The French name, La Manche (“The Sleeve”), is a reference to its shape, which gradually narrows from about 112 mi (180 km) in the west to only 21 mi (34 km) in the east, between Dover, Eng., and Calais, France. Historically both a route for and a barrier to invaders of Britain, it developed into one of the world's busiest sea routes for oil tankers and ore carriers. The Channel Tunnel, completed in 1994, provides a land route between Paris and London.

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or Eurotunnel

Rail tunnel that runs beneath the English Channel between Folkestone, England, and Sangatte (near Calais), France. A rail tunnel was chosen over proposals for a very long suspension bridge, a bridge-and-tunnel link, and a combined rail-and-road link. The 31-mi (50-km) tunnel, which opened in 1994, consists of three separate tunnels, two for rail traffic and a central tunnel for services and security. Trains, which carry motor vehicles as well as passengers, can travel through the tunnel at speeds as high as 100 mph (160 kph).

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Island dependencies, United Kingdom. Located in the English Channel 10–30 mi (16–48 km) off the western coast of France, they cover an area of 75 sq mi (194 sq km) and include the islands of Jersey, Guernsey, Alderney, and Sark and several islets. They are domestically independent of the British government. Structures, including menhirs, are evidence of prehistoric occupation. A part of Normandy in the 10th century AD, the islands came under British rule at the time of the Norman Conquest in 1066. The islets of Ecrehous and Les Minquiers were disputed between England and France until 1953, when the International Court of Justice confirmed British sovereignty. The dispute revived in the late 20th century because sovereignty determines the rights to the continental shelf's economic development (especially petroleum). The Channel Islands were the only British territory occupied by Germany in World War II. The islands are famous for their cattle breeds, including the Jersey and Guernsey.

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Inlet of the Atlantic Ocean, southwestern England. It extends about 85 mi (135 km) between southern Wales and southwestern England, ranging from 5 to 43 mi (8–69 km) wide. Lundy Island, once a pirate stronghold, lies in the centre of the channel; it is maintained as a trust preserve. Ships using the English port of Bristol and the Welsh ports of Swansea and Cardiff pass through the channel.

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