Microviscosity of mucosal cellular membranes in toad urinary bladder: Relation to antidiuretic hormone action on water permeability

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Abstract
The microviscosity of cellular membranes (or membrane fluidity) was measured in suspensions of single mucosal cells isolated from the urinary bladder of the toad,Bufo marinus, by the technique of polarized fluorescence emission spectroscopy utilizing the hydrophobic fluorescent probe, perylene. At 23°C, 5mm dibutyryl cyclic 3′,5′-AMP decreased the apparent microviscosity of the cell membranes from 3.31 to 3.07 P, a minimum decrease of 7.3% (P<0.001) with a physiological time course. Direct visualization of the cell suspension indicated that 98% of the cells were viable, as indicated by Trypan Blue dye exclusion. The fluorescent perylene could be seen only in plasma membranes, suggesting that the measured viscosity was that of plasma membrane with little contribution from the membranes of cellular organelles. Addition of antidiuretic hormone to intact hemibladders stained with perylene produced changes in fluorescence consistent with a similar 7% decrease in apparent microviscosity with a physiological time course. However, finite interpretation of the findings in intact tissue cannot be made because the location and the fluorescent lifetime of the probe could only be conducted on the isolated cells. Comparison with previously determined relationships between water permeability and microviscosity in artificial bilayers suggests that the 7% (a lower limit) decrease in microviscosity would produce only a 6.5% increase in water permeability.