Direct Measurement of the K+-Channel and Its Ion Selectivity in the Thylakoid Membrane from Spinach (Spinacea oleracea L.) Leaves

Thylakoid vesicles were purified from spinach (Spinacea oleracea L. ) leaves by sucrose density gradient centrifugation and incorporated into planar lipid bilayers by stirring. At least one type of voltage-dependent K+ single-channel currents was found. Its conductance (between +60 mV and –60 mV ) was about 55 pS in symmetrical (cis: trans) 250 mmol/L KC1. This channel was sensitive to TEA (tetraethylammonium chloride) and the permeability ratio (PK+/PCl-) was about 14. 9. The selectivity of 55 pS channel determined from both reversal potentials under bi-ionic conditions or from conductance measurements in symmetrical solutions, was in the seguence of K+〉Na+〉Li+ 〉NH4+〉 Cs+. This potassium channel could act as involved in charge-balancing during light-driven proton uptake by thylakoid.