<prompt> The primary active step for sodium reabsorption in the proximal tubule involves:Sodium-glucose cotranspo across the luminal membraneSodiumhydrogen ion counteranspo across the luminal membraneSodium transpo the Na-K-ATPase at the basolateral membraneSodium-amino acid cotranspo across the luminal membrane  <response>: 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. 