, Volume 154, Issue 3, pp 227-237

A Membrane-delimited Effect of Internal pH on the K+ Outward Rectifier of Vicia Faba Guard Cells

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ABA stimulation of outward K+ current (I K,out) in Vicia faba guard cells has been correlated with a rise in cytosolic pH (pH i ). However, the underlying mechanism by which I K,out is affected by pH i has remained unknown. Here, we demonstrate that pH i regulates outward K+ current in isolated membrane patches from Vicia faba guard cells. The stimulatory effect of alkalinizing pH i was voltage insensitive and independent of the two free calcium levels tested, 50 nm and 1 μm. The single-channel conductance was only slightly affected by pH i . Based on single-channel measurements, the kinetics of time-activated whole-cell current, and the analysis of current noise in whole-cell recordings, we conclude that alkaline pH i enhances the magnitude of I K,out by increasing the number of channels available for activation. The fact that the pH i effect is seen in excised patches indicates that signal transduction pathways involved in the regulation of I K,out by pH i , and by implication, components of hormonal signal transduction pathways that are downstream of pH i , are membrane-delimited.

Received: 5 June 1996/Revised: 1 August 1996