Effect of pH and sodium ions on intestinal uptake of lysine in rats

Intestinal uptake of lysine in rats progressively decreased with an increase in pH from 5.2 to 8.5, both in the presence and absence of Na+ ions. At pH 5.2 lysine uptake was 30-35% more than that at neutral pH. Na+ activated lysine uptake by 40-50% at pH 5.2 and it was increased to 110-120% at neutral pH. The observed increase in lysine uptake in response to Na+ and H+ gradients was due to enhanced maximal velocity (Vmax), with little change in affinity constant (Kt). Arrhenius analysis revealed a biphasic curve for lysine uptake with transition temperature (Tc) around 20 degrees C (24 degrees C at pH 5.2 in presence of Na+). The energy of activation (Ea) below (16.1-23.4 Kcal/mole) and above (6.7-8.6 Kcal/mole) the Tc was similar at pH 5.2 and 7.0 both in the presence and absence of Na+ ions. The sensitivity of lysine uptake to various inhibitors was also dependent upon pH and Na+ ions.