Three polyelectrolyte-based tissues, muscle, cornea and lens have been investigated using microelectrode and low angle X-ray diffraction techniques. It has been found that with increasing temperature the net fixed charge in the A- and I-bands in muscle falls, in both the relaxed and rigor states. In the rigor state a definite temperature transition between 27.5 - 30 °C has been established. The sharpness of the off meridional peaks of the 365 Å actin layer line of rigor muscle increases with

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... reasing temperature at low ionic strength. In relaxed muscle previous reports show that the myosin layer-lines disappear with decreasing temperature. We have shown that.the net charge decreases with increasing temperature, as these two phenomena occur within the same temperature range, it is probable that they are connected. All these effects are explained in terms of ion binding models. Previous reports have shown that there is an anomalous negative temperature coefficient of Donnan swelling theory in cornea. We have shown that the net fixed charge decreases linearly with increasing temperature in corneal stroma. This is explained in terms of an ion binding model, which accounts for the negative temperature coefficient. In calf lens no change in the measured Donnan potentials is observed below the critical temperature for the onset of the cold cataract phenomenon. This is probably due to the low concentration of the cryoprotein responsible for this effect. Micromolar concentrations of ATP and PPi have been shown to decrease the fixed negative charge on the myosin molecule in previous work. We have shown that in muscle at zero overlap the lattice spacing and X-ray equatorial intensities are at a maximum at micromolar concentrations of PPi. This effect is interpreted in terms of a change of the electrical regime within the muscle lattice.