| Electromechanical effects in two biological systems were investigated experimentally and theoretically in an attempt to elucidate the mechanisms of transduction operating in both. In the case of the first system, bone, convincing evidence was found that an electrokinetic effect, the streaming potential, is the underlying physical mechanism of transduction. In the case of axon electromechanics, little was discovered about the transduction mechanism due to experimental difficulties.;Experiments on the electromechanical response of the crayfish giant axon were of two types--depolarization in response to stretch and mechanical response to electrical activity. The axon stretch experiments failed to provide reproducible results due mainly to mechanical irregularities introduced by the membrane potential sensing electrode. Although theoretical arguments were advanced suggesting that a mechanoelectric effect known for dielectric materials, electrostriction, might produce a measurable longitudinal force in a voltage-clamped axon, none was detected to a lower limit of 10('-9) Nt.;The similarity of the electrical response of unstressed bone samples through which physiological-strength electrolytes were flowed to the electrical response of bone beams soaked in the same solutions and bent as cantilevers identified streaming as the dominant effect. It was shown by theoretical arguments that only such an experimental study could discriminate between the two proposed mechanisms, piezoelectricity and streaming, as both depend on the rate of loading and stress gradient. |
