Exploring Cellular Water Dynamics Associated With Potassium Ion Changes Using Magnetic Resonance Imaging

Potassium ions play a crucial role in regulating cellular physiology, but their direct effects on water dynamics remain largely unknown. This study aimed to investigate water dynamics in vitro in relation to changes in K⁺ concentration ([K⁺]) using MRI, focusing on the effects of increasing K⁺ concentration on intracellular and extracellular water compartments in terms of cell swelling.

Jurkat cells were used in cell pellet form. Cell swelling was induced under two conditions: elevated extracellular [K⁺] and hypoosmotic stress as a control. For MRI experiments, multi-echo spin-echo and selective inversion-recovery fast spin-echo sequences were used to estimate T₂ and magnetization transfer (MT) parameters, respectively. We evaluated the changes in water dynamics with respect to cell volume changes by estimating the pool size ratio and longitudinal magnetization of the bound and free water pools based on a two-pool model.

T₂ increased under both elevated [K⁺] and hypoosmotic stress conditions, likely due primarily to an increase in the intracellular free water pool. Hypoosmotic stress resulted in a larger increase in free water pool at similar volumetric changes compared to [K⁺] elevation. In both conditions, the bound pool per cell increased linearly with cell volume, but [K⁺] elevation resulted in a smaller increase than hypoosmotic stress.

Using MT and T₂, we demonstrated that both elevated [K⁺] and hypoosmotic stress-induced cell swelling increased T₂, free water pool, and bound pool per cell, but in different patterns, suggesting that K⁺-induced cell swelling involves processes beyond simple osmosis.