Microelectrode studies on Malpighian tubule cells of Locusta migratoria: Effects of external ions and inhibitors

Abstract

Basal and apical membrane potentials were recorded from Malpighian tubules of Locusta using intracellular microelectrodes. Ion substitution experiments, involving Na +, K + and Cl − in the bathing media, indicated that the basal membrane was more permeable to K + than Na + or Cl −. Two different electrical responses to high [K +] salines were noted and these probably reflect distinct physiological states of basal membrane permeability. Experiments with ouabain and orthovanadate suggested that whilst (Na + + K +)-ATPase activity was not significantly electrogenic, asymmetric ionic distribution across the basal membrane was partly maintained by this enzyme. The actions of furosemide and bumetanide indicated that chloride might cross the basal membrane by a cation co-transport mechanism. In addition, data from ion substitution experiments suggest that Cl − entry across the basal membrane is K +-dependent. The responses to Na +-free and Cl −-free salines bring into question the role of Na + in the entry of chloride across the basal membrane by co-transport.