Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA140

Poster Communications

Acute renal tubular lesions compromise the function of the glomerular filtration barrier: a multiphoton microscopy study

C. Gerhard1, K. Fremter1, A. Forst1, M. Hellmuth1, H. Castrop1

1. University Regensburg, Regensburg, Germany.

Albuminuria is a hallmark of kidney disease of various etiologies. Acute lesions of the renal tubular system (acute tubular necrosis) are frequently accompanied by albuminuria, which is considered to be the consequence of a compromised tubular reabsorptive function. Net urinary albumin excretion, however, is also determined by glomerular albumin filtration. Therefore, we hypothesized that in situations of insults to the tubular system, a tubular-glomerular crosstalk may lead to an increased filtration of albumin and consequently may contribute to the development of albuminuria. To test this hypothesis, we used intravital multiphoton microscopy in Munich Wistar Froemter rats to determine the glomerular sieving coefficient (GSC) of albumin after ablation of single cells of the proximal tubule in an otherwise healthy kidney. For intravital imaging, rats were anesthetized with 100 mg/kg Ketamin, 3.45 mg/kg Xylazin and 2 mg/kg Midazolam i.m.. Single tubular cells were ablated by focused laser exposure. The GSC of albumin was determined after i.v. infusion of Alexa-594-labeled albumin as the ratio of the fluorescence intensities in Bowman's space/the glomerular capillary lumen, corrected by the background intensities. The density of the glomerular endothelial glycocalyx was determined after i.v. application of wheat germ agglutinin. The GSC of albumin in the healthy rat kidney was low, averaging 0.0008 ± 0.0002. Within 20 min after laser ablation of a few proximal tubular cells, the albumin GSC of the affected nephron increased rapidly to 908 ± 287% of baseline (p<0.01 vs. baseline; n=25), whereas the albumin GSC of neighboring nephrons remained unchanged (p=ns). In parallel with the albumin leakiness of the glomeruli of the affected nephrons, the density of the glomerular endothelial glycocalyx declined, averaging 18.3 rU in controls and 14.2 rU after tubular lesions (p<0.0001; n=215 regions of interest). Furthermore, we occasionally observed changes in the shape of the podocyte cell bodies. In summary, using intravital multiphoton microscopy, we found a nephron-specific marked increase in the GSC of albumin in response to acute insults to the proximal tubule. Our data further suggest a crucial involvement of the endothelial glycocalyx in the function of the glomerular filtration barrier and provide first evidence for a functional modulation of the integrity of the glomerular filtration barrier by the tubular system.

Where applicable, experiments conform with Society ethical requirements