Ionophoretic stimulation of K+-ATPase of oxyntic cell microsomes

The K⁺ -selective ionophores valinomycin, trinactin, nigericin, and gramicidin stimulated the K⁺-ATPase of oxyntic cell microsomes as much as 5 fold. Gramicidin altered the K⁺ activation kinetics: while the V_max greatly increased, the K_a for K⁺ shifted only slightly. Activation also occurred with lyophilization, repeated freezing and thawing and nonionic detergents. The results are consistent with one population of membranes being freely permeable to K⁺ (source of the K⁺-dependent activity in absence of ionophore) and another population being impermeable to K⁺. The K⁺-ATPase in these latter vesicles would be activated by the appropriate ionophore or membrane disruptive procedure.