Micropuncture of superficial nephrons in avian (Sturnus vulgaris) kidney.
Single nephron glomerular filtration rate (SNGFR), fluid absorption, and tubule transport of sodium, chloride, calcium, magnesium, potassium, and phosphate were evaluated under control (2.5% mannitol infusion) conditions by micropuncture of superficial, reptilian-type nephrons of European starlings (Sturnus vulgaris). SNGFR averaged 0.36 nl . min-1 . Sodium, chloride, and water were transported at equivalent rates with about 24% of the filtered load absorbed up to the point of micropuncture. Calcium was absorbed continuously along these tubules in excess of sodium and fluid, whereas magnesium appeared to undergo net secretion early and net absorption late in the tubules. Potassium transport varied considerably, with all tubules from a single bird generally showing either net potassium absorption or no net transport. In the latter group, data for a few tubules suggested net potassium secretion. For phosphate, individual tubules from a single bird were capable of either net absorption or net secretion. Mean fractional delivery of phosphate for all tubules was 1.62, but secretion rates apparently can exceed filtration rates for phosphate by as much as 6 times.
D000818:Animals; D001717:Birds / Q000502:physiology*; D001774:Blood Chemical Analysis; D002404:Catheterization / Q000379:methods; D004573:Electrolytes / Q000097:blood / Q000378:metabolism*; D004577:Electron Probe Microanalysis; D005919:Glomerular Filtration Rate; D008274:Magnesium / Q000378:metabolism; D009399:Nephrons / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D014462:Ultrafiltration
D004573:Electrolytes; D010710:Phosphates; D008274:Magnesium