A cartoon published last year in a Boston newspaper showed two passengers on an aeroplane, one turning to the other to say, “Uh-oh, the stewardesses have changed into their Cuban costumes.” Seventy-five successful hijackings of aircraft of United States and foreign registration in the past nineteen months have dampened this light-hearted approach to the subject. In recent months a bantering remark to a member of a flight crew as to the prospects for a side trip to Cuba has earned more than one passenger a delayed flight, a conversation with an agent of the Federal Bureau of Investigation, or an appearance in court on charges ranging from disturbing the peace to attempted aircraft piracy. For some passengers the hijacking of an aircraft may be a colorful interlude in the routine course of air travel; for the flight crew, the carrier, and the Federal Aviation Administration, it is a nightmare, a vicious form of Russian roulette in which the fate of the hijacker is inconsequential in comparison with the potential cost in lives of passengers and crew, not to speak of the value of the aircraft itself.
We have recently described the construction of a dual-cell, nonlinear dielectric spectrometer, and its application to the study of cell suspensions of S. cereuisiae (A.M. Woodward and D.B. Kell, Bioelectro-them. Bioenerg., 24 (1990) 83). Substantial, odd harmonics were generated by these cells when stimulated by very modest sinusoidal electrical fields, within fairly sharp voltage-and frequency windows (ca. 0.8-2.5 V cm-', l-50 Hz). Resting cells were found to generate only odd-numbered harmonics. In the present work, we have simultaneously applied two sinusoidal frequencies which were indiuidually of unsuitable frequency and/or amplitude for the generation of harmonics when applied to suspensions of S. cerevisiae. Strong "sidebands" or "beat frequencies" were observed which were the (odd-numbered) sums and differences of the exciting frequencies (viz. fi f 2f2, f2 +2f,). The generation of these beat frequencies was strongly inhibited by low concentrations of sodium metavanadate, suggesting that they may be ascribed largely to the H+-ATPase present in the plasma membranes of these cells. We show that the ability of dc fields to inhibit the manifestation of nonlinear dielectric behaviour by these cells is explicable in terms of their ability to act as a field of zero Hz, forcing the excitation out of the amplitude window. When the cells were allowed to glycolyse, beat frequencies of even order (fi f f*, fi f 3fi) were observed. The present approach provides a novel and powerful approach to the registration of nonlinear dielectric spectra, which, due to the greater precision inherent in the discrimination of frequencies rather than voltages may be expected to provide a more sensitive means of detecting nonlinear dielectric properties in biological systems. If the transduction of exogenous electrical field energy recorded by this method is representative of the natural turnover of the H+-ATPase in viva, it may be calculated that the efficiency of the capture of electric field energy by this enzyme is some 3%.
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