Membrane Potentials and Ion Permeabilities in Flexor Cells of the Laminar Pulvini of Phaseolus Coccineus L

The internal potential of flexor cells in slices of the laminar pulvini of Phaseolus coccineus has been recorded by standard microelectrode techniques in 100 eq m(-3) external salt solutions of various ionic compositions. The measured values are between-15 and-60 mV depending on the external medium. Treating the results with the Goldman equation yields the following relative permeabilities: K(+), 1.00; Na(+), 0.24; Cl(-), 0.19; NO 3 (-) , 1.6. The membrane potential was only slightly sensitive to external pH and Ca(2+). Metabolic inhibitors (azide, cyanide and salicylhydroxamic acid, carbonyl cyanid m-chlorphenyl hydrazone) caused only slight depolarizations (ca. 4 mV), which differed from the ion-induced changes by their slow time courses. The results are consistent with the hypothesis that the relatively impermeable Cl(-) is actively transported and osmotically efficient, whereas the well-permeable K(+) passively follows Cl(-) to maintain electroneutrality and is osmotically of only minor significance.