Adenosine is an important molecule for maintaining physiological function of the kidney and plays a role in the protection against ischemic kidney injury, but the exact distribution of adenosine in the kidney has not been elucidated. Matrix-assisted laser desorption/ionization - imaging mass spectrometry (MALDI-IMS) is a technology used for visualizing the in situ distributions of molecules and we aimed to visualize physiological distribution of adenosine in murine kidney by MALDI-IMS.Design and Method:
Kidneys from eight-week-old mice anesthetized by isoflurane were harvested and frozen by liquid nitrogen within a second (snap-frozen sections) or a minute (slowly-frozen sections) after cutting blood vessels. The distribution of small molecule metabolites were examined by matrix-assisted laser desorption/ionization - imaging mass spectrometry (MALDI-IMS) and hematoxylin and eosin stain.Results:
Physiologically important low-molecular weight metabolites were successfully visualized and remarkable accumulation of adenosine in the corticomedullary boundary zone, especially in the outer stripes of outer medulla (OSOM), was identified in the snap-frozen sections. The significant accumulation of adenosine disappeared in the ischemic sections frozen at a minute after dissection. Although adenosine is usually caused by augmented degradation of phosphorylated adenylates, adenosine triphosphate and adenosine diphosphate were both rich in the OSOM of the snap-frozen sections. Therefore, the accumulation of adenosine in the OSOM was suggested not to be caused by the degradation of phosphorylated adenylates alone.Conclusions:
A physiological accumulation of adenosine in the OSOM would contribute to effective activation of A2-ARs, which require a higher concentration of adenosine for activation, and vasodilatation which leads to increase in the medullary blood flow and protects medulla from hypoxic injury. MALDI-IMS with snap-frozen procedure would contribute to deeper understanding of renal physiology because the distribution of small molecules itself may determine the site of significant action.