The primary active step for sodium reabsorption in the proximal tubule involves:
Sodium transpo the Na-K-ATPase at the basolateral membrane. This is the only transpo step for sodium in the proximal tubule that involves the direct input of energy to move sodium against its electrochemical gradient (in this case from the inside of the cell to the outside).
Sodium-glucose cotranspo across the luminal membrane
Sodium/hydrogen ion counteranspo across the luminal membrane
Sodium transpo the Na+-K+-ATPase at the basolateral membrane
Sodium-amino acid cotranspo across the luminal membrane