Morphological changes in the renal macula densa during natriuresis and diuresis

Area of Science:

• Nephrology
• Cell Biology
• Renal Physiology

Background:

• The macula densa plays a crucial role in regulating kidney function.
• Understanding its cellular morphology is key to comprehending renal physiology.
• Previous studies have not fully elucidated the dynamic changes in macula densa cell structure during diuresis.

Purpose of the Study:

• To investigate the morphological alterations of the macula densa in response to diuretic agents.
• To examine the relationship between diuretic-induced natriuresis/diuresis and changes in macula densa intercellular spaces.
• To identify novel cellular structures within the macula densa.

Main Methods:

• Anesthetized dogs underwent renal artery infusion of diuretic agents (frusemide, ethacrynic acid, mannitol) or saline.
• Kidneys were rapidly fixed via high-pressure perfusion with glutaraldehyde.
• Electron microscopy was used to examine the ultrastructure of the macula densa cells, focusing on basolateral intercellular spaces.

Main Results:

• Infusion of frusemide, ethacrynic acid, or mannitol significantly reduced the size and number of basolateral intercellular spaces between macula densa cells.
• Intravenous saline infusion also led to the closure of these intercellular spaces.
• No direct correlation was found between plasma renin activity and the observed changes in intercellular spaces.
• A unique membrane-bound, vesicle-containing structure was identified between macula densa cell processes.

Conclusions:

• The observed reduction in basolateral intercellular spaces suggests a role in regulating fluid movement across the macula densa.
• These morphological changes likely reflect alterations in fluid flux between the distal tubule and the juxtaglomerular apparatus interstitium.
• The newly identified cellular structure warrants further investigation into its functional significance in renal physiology.