Evidence for a stimulatory effect of high potassium diet on renal kallikrein

Considerable evidence indicates that the connecting tubule cells, a type of cell of the distal nephron which seems to participate on potassium secretion, may be the place where renal kallikrein is synthetized. As potassium secretion and kallikrein synthesis may occur in the same cells, we studied the effect of high potassium diet on renal kallikrein production. The kallikrein containing cells from rats fed a normal and high potassium diet were evaluated using a combination of morphometric analysis, conventional electron microscopy, and ultrastructural immunocytochemistry. High potassium diet produced hypertrophy and hyperplasia of the kallikrein containing cells. Hyperplasia was sustained by an increased number of immunoreactive cells/mm² (151 ± 14 vs. 86.4 ± 12, P < 0.01), an increased number of binucleated immunoreactive cells/mm2 (11.90 ± 2.1 vs. 3.77 ± 0.17, P < 0.005), and by the presence of mitosis. Cell hypertrophy was sustained by an increased cross-sectional area of immunoreactive cells (μ²) (320.4 ± 21 vs. 104.5 ± 6.1, P < 0.001), by an increased area of basal plasma membrane infoldings, by an hypertrophy of the components of the Golgi complex, hypertrophy of the components of the rough endoplasmic reticulum, and by a larger number of secretory-like vesicles containing kallikrein. The rats fed with high potassium diet had higher values on urinary kallikrein excretion-amidase activity (3.70 ± 0.51 vs. 2.01 ± 0.37 units/day, P < 0.02), higher values on potassium excretion (18.8 ± 1.7 vs. 1.31 ± 0.1 mmol/day, P < 0.001), and higher urinary volume (51.5 ± 5.3 vs. 12.2 ± 1.6 ml/day, P < 0.001). The increased size of the kallikrein containing cells correlated with kallikrein excretion (r = 0.7013, P < 0.002). These results suggest that high potassium diet stimulates the kallikrein containing cells of the distal nephron producing hyperplasia and hypertrophy. Taken the ultrastructural changes together with the increased urinary excretion of kallikrein, the results suggest that a high potassium diet increased the synthesis and secretion of kallikrein. The nature of this stimulatory effect cannot be elucidated from the present study.