Define the Counter transport - Secondary Active Transport

If the two substances which transport is coupled, move in opposite directions, the phenomenon is known as counter transport or antiport, for example in proximal convoluted tubules of kidneys, sodium is actively reabsorbed. At the same time, for each sodium ion reabsorbed, one hydrogen ion is transported by similar carrier into the lumen of the tubule. Some instances of transport by solute-solvent interactions are secondary to the active transport of some substance.