Electrophysiological Evidence for an Electrogenic Proton Pump and the Proton Symport of Glucose in the Marine FungusDendryphiella salina

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Abstract
The marine hyphomycete Dendryphiella salina (Suth.) Nicot & Pugh has a resting membrane potential of −250 mV (inside negative). The respiratory inhibitors sodium azide and FCCP induced a rapid but reversible depolarization of the membrane of at least 180 mV; sodium azide also caused alkalinization of the medium. Vanadate brought about significant depolarization but this was not always reversible. EDTA induced depolarization though to a lesser extent. DIDS and SITS caused a depolarization of around 30–70 mV which was readily reversible, N-ethylmaleimide irreversibly depolarized the membrane by 180–200 mV. Ouabain had no effect. When external concentrations of H+ , K+ , Na+ or Cl− were changed singly, only changes in H+ affected membrane potential, with shifts decreasing with increasing pH. Glucose and 3-O-methyl glucose depolarized the membrane in a concentration-dependent manner which was enhanced by starvation of the hyphae. Recovery occurred in the presence of the hexose. Glucose caused an alkalinization of the medium, with time characteristics similar to the membrane potential changes. It is concluded that there is an electrogenic proton pump and a proton—glucose symporter in D. salina. The retention of proton-based transport systems suggests a terrestrial origin for the fungus.