Channel-mediated K(+) flux in barley aleurone protoplasts

Gibberellic acid (GA3) stimulates K(+) efflux from the barley (Hordeum vulgare L. cv. Himalaya) aleurone. We investigated the mechanism of K(+) flux across the plasma membrane of aleurone protoplasts using patch-clamp techniques. Potassium-ion currents, measured over the entire surface of the protoplast plasma membrane, were induced when the electrochemical gradient for K(+) was inward (into the cytoplasm). The magnitude and voltage-dependence of this inward current were the same in protoplasts treated with GA3 and in control protoplasts (no GA3). Inward currents activated by negative shifts in the membrane potential (EM) from the Nernst potential for K(+) (EK) showed membrane conductance to be a function of the electrochemical gradient (i.e. EM-EK). Single-channel influx currents of K(+) were recorded in small patches of the plasma membrane. These channels had a single-channel conductance of 5-10 pS with 100 mM K(+) on the inside and 10 mM K(+) on the outside of the plasma membrane. Single-channel currents, like whole-cell currents, were the same in protoplasts treated with GA3 and control protoplasts. Voltage-gated efflux currents were found only in protoplasts tha thad been incubated without GA3. We conclude that K(+) influx in the aleurone is mediated by channels and these membrane proteins are not greatly effected by GA3.