Membrane potentials and ion permeabilities in flexor cells of the laminar pulvini of Phaseolus coccineus L.

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Abstract
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 Ca2+. 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.