Abstract
To elucidate the morphological counterpart of the tubulo-glomerular feedback mechanism, kidneys of male rats were perfused for a short time with different ion solutions and at different pressures, then fixed for thin-section electron microscopy. The macula densa of distal tubules specifically responded to such perfusion conditions with the widening of intercellular spaces, whereas other parts of the renal tubules did not show any appreciable changes in epithelial structures. The intercellular spaces of the macula densa widened most extensively when perfused with 140 mM NaCl and less extensively with 140 mM NaHCO3, but remained almost entirely closed with 140 mM CH3COONa and 70 mM CaCl2. When perfused at different pressures using the same solution, the intercellular spaces were widest at the perfusion pressure of 80 mmHg, and were narrower in the order of 40, 120 and 160 mmHg. The present observations are well consistent with the physiological analysis reported previously. Thus, the macula densa may change the intercellular space in response to the ion composition and possibly pressure of urine running down the distal tubule, suggesting its involvement in the tubulo-glomerular feedback mechanism.
