Answer: Ouabain is a cardiac glycoside that inhibits the Na-K-ATPase membrane pump, resulting in an increase in intracellular sodium and calcium concentrations. Increased intracellular concentrations of calcium may promote activation of contractile proteins (e.g., actin, myosin).
The Na/glucose cotransporter is a protein that facilitates the transport of glucose into cells by coupling it with the transport of sodium ions. Since ouabain inhibits the active transport of sodium ions out of the cell, it would lead to an increase in intracellular sodium concentration and a decrease in extracellular sodium concentration. This would result in a decrease in the activity of the Na/glucose cotransporter, which would reduce the rate of glucose transport into the cell.
The transport protein directly affected by ouabain is the Na-K-ATPase membrane pump