TY - JOUR
T1 - Some effects of trinitrocresolate and valinomycin on Na and K transport across thin lipid bilayer membranes
T2 - A steady-state analysis with simultaneous tracer and electrical measurements
AU - Ginsburg, H.
AU - Tosteson, M. T.
AU - Tosteson, D. C.
PY - 1978/6
Y1 - 1978/6
N2 - This paper describes the effect of trinitrocresolate anions (TNC-) on the electrical conductance (Gm), and tracer-measured unidirectional Na and K fluxes (MNa and MK) 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 (<10-12 moles cm-2 sec-1). In the presence of TNC- (10-2m), Gm 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 from Gm. 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 (10-6m) and no TNC-, both the ion fluxes and Gm 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 (10-6m) and TNC- (10-2m), this selectivity disappeared in that both Gm and MNa 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. Both Gm and Mx 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.
AB - This paper describes the effect of trinitrocresolate anions (TNC-) on the electrical conductance (Gm), and tracer-measured unidirectional Na and K fluxes (MNa and MK) 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 (<10-12 moles cm-2 sec-1). In the presence of TNC- (10-2m), Gm 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 from Gm. 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 (10-6m) and no TNC-, both the ion fluxes and Gm 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 (10-6m) and TNC- (10-2m), this selectivity disappeared in that both Gm and MNa 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. Both Gm and Mx 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.
UR - http://www.scopus.com/inward/record.url?scp=0018083002&partnerID=8YFLogxK
U2 - 10.1007/BF01885368
DO - 10.1007/BF01885368
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C2 - 702517
AN - SCOPUS:0018083002
SN - 0022-2631
VL - 42
SP - 153
EP - 168
JO - Journal of Membrane Biology
JF - Journal of Membrane Biology
IS - 2
ER -