Melatonin Facts: Musing With the Concept "Melatonin Travels Freely Through Biological Membranes"

Area of Science:

• Biochemistry
• Cell Biology
• Endocrinology

Background:

• Melatonin is known to freely cross biological membranes.
• The implications of melatonin's membrane permeability, particularly during experimental sample preparation, have been overlooked.
• Previous research has not adequately considered melatonin's diffusion properties.

Purpose of the Study:

• To highlight the underappreciated consequences of melatonin's free diffusion through biological membranes.
• To emphasize the need to account for melatonin diffusion in experimental design and data interpretation.
• To critically re-evaluate existing data concerning local melatonin production.

Main Methods:

• This study is a critical review and theoretical analysis of melatonin's physicochemical properties.
• It examines the behavior of melatonin during ex vivo, in cellulo, and subcellular sample preparation.
• The analysis focuses on melatonin's inability to be retained within cellular compartments or organelles.

Main Results:

• Melatonin readily diffuses out of biological samples, including organs and cells, during preparation.
• Melatonin cannot be retained or "trapped" within membrane-bound organelles such as mitochondria, the nucleus, ER/Golgi, or lipid droplets.
• Existing experimental data may be confounded by melatonin's diffusion.

Conclusions:

• Existing data on melatonin localization and production requires careful reinterpretation due to its diffusion.
• Future research investigating local melatonin production outside the pineal gland and retina must incorporate melatonin's diffusion characteristics.
• Experimental methodologies need to be adapted to prevent melatonin loss from samples.