A role for podocytes to counteract capillary wall distension

In a previous study of the changes in glomerular structure in the isolated perfused kidney (IPK), perfusion at high pressures lead to an enlargement of the glomerular tuft and to the formation of giant capillaries. The present paper analyzes the morphological and dimensional changes of the peripheral glomerular capillary wall under these circumstances. The enlargement of glomerular capillaries at high pressure perfusion was accompanied by a considerable increase in the surface area of the glomerular basement membrane (GBM). The podocyte as well as the endothelial layer perfectly adapted to the acute challenge in covering increasing GBM area. The interdigitating foot process pattern showed up in an ideal arrangement. The capillary wall expansion was associated with a significant increase in total pericapillary slit area. Compared to the corresponding low pressure groups (65 mm Hg, without and with the application of vasodilators) the slit area increased in the high pressure groups (105 mm Hg, without and with vasodilator) by approximately 50 and 75%, respectively. This increase of the slit area was mainly due to an increase in slit length; the slit width remained fairly constant. These findings indicate that the pericapillary wall is distensible based on a distensibility of the GBM. We suggest that the contractile apparatus of podocyte foot processes regulates the expansion of the GBM.