Rubidium reduces potassium permeability and fluid secretion in Malpighian tubules of Locusta migratoria, L.
The basal membrane potential (V(b)) 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 V(b) hyperpolarized from a mean resting potential of -72.1 mV to -90.1 mV. On substituting rubidium for potassium in the control saline, V(b) 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 approximately 50% reduction in the rate of fluid secretion. The action of inhibitors on V(b) in the presence of rubidium showed that V(b) under these conditions probably originated from the bafilomycin-sensitive electrogenic potential generated across the apical membrane by a V-type ATPase. The responses of V(b) 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.
Department of Biological Sciences, University of Durham, South Rd, DH1 3LE, Durham, UK
D
D
Hyde
P
P
Baldrick
S L.
SL
Marshall
J H.
JH
Anstee