Effects of Intracellular Vanadate on Electrogenesis, Excitability and Cytoplasmic Streaming in Nitellopsis obtusa

Vanadate, which is known to inhibit the plasma membrane H^$-ATPaseof Neurospora, was applied intracellularly to internodal cellsof Nitellopsis by use of the intracellular perfusion technique.It inhibited electrogenesis and H^$-extrusion, evidence thatthe electrogenic pump of the Characeae plasmalemma is the H^$-extrudingone. The concentration of vanadate for the half-maximal inhibitionof the activity of the pump was 5 µM. The membrane potentialand H^$-extrusion occasionally recovered from vanadate inhibitionsfor reasons that are unknown. Membrane excitability, which isdependent on Mg?ATP, was not inhibited by vanadate, which suggeststhat the ATPase involved with membrane excitability differsfrom that of the H^$ pump. Cytoplasmic streaming took place evenwhen the cell was perfused with the medium containing 1 mM vanadate,which indicates that the vanadate-insensitive actomyosin systemis concerned with the motive force generation of the streaming. (Received August 27, 1981; Accepted April 13, 1982)