Some effects of trinitrocresolate and valinomycin on Na and K transport across thin lipid bilayer membranes: A steady-state analysis with simultaneous tracer and electrical measurements

Abstract
This paper describes the effect of trinitrocresolate anions (TNC) on the electrical conductance (G m ), and tracer-measured unidirectional Na and K fluxes (M Na andM K) across bilayers formed from sheep red cell lipids dissolved in decane. In the absence of TNC, typical low conductances were observed, while the cation fluxes were too low to measure by our techniques (−12 moles cm−2 sec−1). In the presence of TNC (10−2 m),G m increased and TNC was the main charge carrier in the system. The cationic fluxes were also much increased, but the membranes showed no significant selectivity between K and Na. Furthermore, the Na and K fluxes were at least two orders of magnitude larger than the ionic fluxes calculated fromG m . Thus, almost all of the K and Na transport across the membrane in the presence of TNC is electrically silent and is probably carried out as KTNC and NaTNC ion pairs. In the presence of valinomycin (10−6 m) and no TNC, both the ion fluxes andG m were 103 times larger in KCl than in NaCl, thus exhibiting the characteristic high selectivity of valinomycin for K over Na. In the presence of both valinomycin (10−6 m) and TNC (10−2 m), this selectivity disappeared in that bothG m andM Na in the NaCl system were similar to the respective values in the KCl system. Even under these conditions, most of the Na is still transported by a process which does not carry charge. BothG m andM x increased alike and monotonically with increasing temperature over the range 7 to 30°C. In the absence of TNC the enthalpies of activation were invariably higher in KCl than in NaCl. Addition of TNC produced equal enthalpies of activation for both Na and K containing systems suggesting a common, temperature-dependent, ratedetermining step in charge transfer and the electrically silent cation fluxes.