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The role of the macula densa in renin release: studies by microperfusion
Abstract:
The role of the macula densa in control of renin release and in mediation of tubulo-glomerular feedback was investigated following orthograde microperfusion in Munich Wistar rats. Tubules of surface glomeruli were perfused, drip-fixed with glutaraldehyde and biopsy cores taken containing perfused and non-perfused glomeruli. Serial sections were examined by light and electron microscopy. In some animals dilated basolateral spaces were observed between cells in control maculae densa but no spaces were found following microperfusion with hypertonic NaCl, isotonic mannitol or hypotonic NaCl containing 1 mg/l frusemide. In other animals no spaces were found in control cores, and perfusion with the above solutions had no effect. However, in such animals, tubules perfused with hypotonic NaCl (71 mmol/kg H2O) had prominent basolateral spaces in their maculae densa. The presence of dilated basolateral intercellular spaces is generally associated with osmotically driven water flow. The extent of dilatation of such spaces in the macula densa is correlated with transepithelial osmotic or ionic gradients and may indicate activity of these cells in the recognition of distal tubular fluid composition.
Insights
The macula densa cells
Area of Science:
- Nephrology
- Renal Physiology
- Cell Biology
Background:
- The macula densa plays a crucial role in regulating renal function.
- Understanding its cellular mechanisms is key to comprehending tubulo-glomerular feedback and renin release.
Purpose of the Study:
- To investigate the role of the macula densa in controlling renin release.
- To elucidate the macula densa's involvement in mediating tubulo-glomerular feedback.
- To examine the structural changes in macula densa cells in response to varying tubular fluid compositions.
Main Methods:
- Orthograde microperfusion of tubules in Munich Wistar rats.
- Drip-fixation with glutaraldehyde and biopsy core collection.
- Examination of serial sections using light and electron microscopy.
Main Results:
- Dilated basolateral intercellular spaces in macula densa cells were observed under specific conditions.
- Perfusion with hypertonic NaCl, isotonic mannitol, or hypotonic NaCl with frusemide did not induce these spaces.
- Hypotonic NaCl perfusion (71 mmol/kg H2O) led to prominent basolateral spaces, suggesting osmotic water flow.
- The extent of space dilatation correlated with transepithelial osmotic or ionic gradients.
Conclusions:
- The macula densa exhibits structural changes indicative of osmotic water flow.
- These changes are linked to transepithelial gradients, suggesting a role in sensing distal tubular fluid composition.
- This cellular activity may be integral to the macula densa's function in regulating renin release and tubulo-glomerular feedback.