Brain microsomes bind ryanodine and contain ryanodine-sensitive calcium channels.

Under a given set o f conditions (including the relative concentrations of the macromolecular components), the polymer was said to interact with PGM if the components in the mixture sedimented with a larger sedimentation coefficient than the controls after concentration effects had been taken into account (Table l a ) . PGM concentrations were kept fixed (2.0 mg/ml) and the DEAE-dextran concentrations were varied (from 0.6 to 3.4 mg/ml): up to a DEAEdextran concentration of 1.9 mg/ml, s?,, values for the faster moving PGM component showed a steady increase (Table l a ) compared with the PGM controls, strongly indicative of an interaction. The increase in sedimentation coefficient of the PGM in the mixture cell (compared with the controls) was in the same sense as increase in turbidity of the suspension and loss o f apparent areas under the Schlieren boundaries. At higher values of DEAE-dextran concentration the s 2 , , fell back to near the 'control' value again: this would appear to suggest that the interaction is very concentration sensitive, although the effects of the increased viscosity on increasing the concentration o f the slower moving component ( D E A E dextran) cannot be excluded. Increase of the ionic strength in two separate experiments (Table 1 b and 1 c) also showed loss of interaction, indicating that the interactions between PGM and the polymer are electrostatic in nature. In conclusion, the increases in (apparent) Sedimentation coefficient of the PGM (and also DEAE-dextran) observed could be a direct result o f the loss of concentration o f PGM and DEAE-dextran in forming large turbid aggregates. Attempts at a more exact quantitative description of the interaction is difficult because of the presence of JohnstonOgston [7]-related effects. These aspects, together with a consideration of the complications arising from the presence of other potentially interacting substances in the gastrointestinal tract (e.g. bile salts) and a comparison o f interactions with other cationic and bifunctional polymers (and also non-interaction with polyanionics) will be considered in a future publication.