Diffusion of water in cat ventricular myocardium

Area of Science:

• Physiology
• Biophysics
• Biomaterials Science

Background:

• Understanding solute and solvent transport across myocardial tissue is crucial for drug delivery and physiological studies.
• Previous models often struggle to reconcile diffusional resistance with tissue water content.
• Accurate diffusion coefficients are needed for modeling physiological processes in the heart.

Purpose of the Study:

• To investigate the diffusion rates of tritiated water (THO) and [14C]sucrose across cat right ventricular myocardium.
• To evaluate the suitability of different diffusion models (parallel pathway, dead-end pore, cell-matrix) for explaining observed diffusion data.
• To determine the effective diffusion coefficients and diffusion space volumes for water and sucrose within the myocardium.

Main Methods:

• Diffusion experiments were conducted using an Ussing-type diffusion cell at 23°C.
• Concentration changes of THO and [14C]sucrose were monitored over 4-6 hours.
• Data were analyzed using parallel pathway, dead-end pore, and cell-matrix diffusion models.

Main Results:

• The extracellular diffusion space for sucrose was 23% of the tissue volume.
• The effective intramyocardial sucrose diffusion coefficient (Ds) was approximately 22.6% of its free diffusion coefficient.
• The cell-matrix model provided the most consistent interpretation, estimating water diffusion coefficients in cellular and extracellular fluids at ~25% of the free diffusion coefficient.

Conclusions:

• Simpler diffusion models (parallel pathway, dead-end pore) are inadequate for simultaneously explaining myocardial diffusional resistance and water content.
• The cell-matrix model offers a more accurate representation of heterogeneous diffusion within the myocardium.
• This study provides key parameters for understanding water and solute transport in cardiac tissue.