Studies of the ionic basis of the action potential in squid giant axon found that a. decreasing potassium outside the cell increases the size of the action potential. b. decreasing sodium outside the cell increases the size of the action potential. c. decreasing potassium outside the cell decreases the size of the action potential. d. manipulating sodium has large effects on both the size of the action potential and the resting membrane potential. e. decreasing sodium outside the cell decreases the size of the action potential.