Cell water viscosity

This chapter focuses on the technique used to obtain information relevant to cellular aqueous viscosity. Measuring the viscosity under conditions that perturb the cellular aqueous compartment is important in elucidating the role of viscosity in relation to a variety of physiological responses. By using the proper type of study, the compartmentalization of the cytoplasm can also be related to cytoplasmic viscosity. The electron spin resonance (ESR) technique is used to obtain information relevant to cellular aqueous viscosity. The ESR technique employing spin labels is used to measure translational motion and rotational motion. It involves the use of spin labels to measure rotational motion through the parameter known as “rotational correlation time.” The rotational motion of a spin label in a solid agar block is essentially identical to that dissolved in bulk water. The treatment indicates that the measurement of viscosity by distance-dependent, spin labe–spin label collisional events, where the spin label concentration is known, yields different and preferred information as compared to diffusional information that is inferred from rotational motion data.