Rubidium reduces potassium permeability and fluid secretion in Malpighian tubules of Locusta migratoria, L

The basal membrane potential (Vb) of Locusta Malpighian tubule cells in control saline results from its relatively high permeability to potassium. In the presence of 1 mM barium added to the control saline Vb hyperpolarized from a mean resting potential of −72.1 mV to −90.1 mV. On substituting rubidium for potassium in the control saline, Vb also hyperpolarized to a value of −91.4 mV. Rubidium was also similarly effective in hyperpolarizing the basal membrane even in the presence of control concentrations of potassium in the bathing medium. Substitution of rubidium for potassium also effected a ∼50% reduction in the rate of fluid secretion. The action of inhibitors on Vb in the presence of rubidium showed that Vb under these conditions probably originated from the bafilomycin-sensitive electrogenic potential generated across the apical membrane by a V-type ATPase. The responses of Vb to potassium, barium and rubidium and their inhibition of fluid secretion suggest the presence of a substantial rubidium-blockable potassium conductance located on the basal membrane of Locusta Malpighian tubule cells.