Recognition and processing of randomly fluctuating electric signals by Na,K-ATPase.
Previous work has shown that Na,K-ATPase of human erythrocytes can extract free energy from sinusoidal electric fields to pump cations up their respective concentration gradients. Because regularly oscillating waveform is not a feature of the transmembrane electric potential of cells, questions have been raised whether these observed effects are biologically relevant. Here we show that a random-telegraph fluctuating electric field (RTF) consisting of alternating square electric pulses with random lifetimes can also stimulate the Rb(+)-pumping mode of the Na,K-ATPase. The net RTF-stimulated, ouabain-sensitive Rb+ pumping was monitored with 86Rb+. The tracer-measured, Rb+ influx exhibited frequency and amplitude dependencies that peaked at the mean frequency of 1.0 kHz and amplitude of 20 V/cm. At 4 degrees C, the maximal pumping activity under these optimal conditions was 28 Rb+/RBC-hr, which is approximately 50% higher than that obtained with the sinusoidal electric field. These findings indicate that Na,K-ATPase can recognize an electric signal, either regularly oscillatory or randomly fluctuating, for energy coupling, with high fidelity. The use of RTF for activation also allowed a quantitative theoretical analysis of kinetics of a membrane transport model of any complexity according to the theory of electroconformational coupling (ECC) by the diagram methods. A four-state ECC model was shown to produce the amplitude and the frequency windows of the Rb(+)-pumping if the free energy of interaction of the transporter with the membrane potential was to include a nonlinear quadratic term. Kinetic constants for the ECC model have been derived. These results indicate that the ECC is a plausible mechanism for the recognition and processing of electric signals by proteins of the cell membrane.
Xie
T D
TD
Department of Biochemistry, University of Minnesota, St. Paul 55108.
Marszalek
P
P
Chen
Y D
YD
Tsong
T Y
TY
D055592:Biophysical Phenomena; D001703:Biophysics; D004563:Electrochemistry; D004910:Erythrocyte Membrane / Q000201:enzymology; D006801:Humans; D066298:In Vitro Techniques; D016623:Ion Pumps / Q000378:metabolism; D008564:Membrane Potentials; D008956:Models, Chemical; D011487:Protein Conformation; D012413:Rubidium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood / Q000737:chemistry*
D016623:Ion Pumps; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium