title: Flow-correlated influx of K, Ca, P, and Mg during continuous microperfusion of the loop of Henle in the rat.
abstract: Investigations on hydropenic rats were undertaken enabling us to determine the relative loop influx rates for potassium, calcium, magnesium, and phosphorus during end proximal continuous microperfusions at 15 or 35 nl . min-1 with saline free of these ions. Replicate quantitative collections were taken at collected flow rates of 9 or 26 nl . min-1. Element concentrations were determined by electron probe analysis. Results showed a significant influx of all four ions in the fluid collected at the early distal site, with magnesium showing the smallest entry rate. As expected, calcium and potassium concentrations at the early distal site increased with the perfusion flow rate. In contrast, phosphorus concentration decreased with flow. Phosphorus concentration at low flow was 0.43 +/- 0.06 mmole . liter-1 vs. 0.25 +/- 0.03 at high flow (P less than 0.01). However, increasing influx was seen with increasing flow for phosphorus (r = 0.58, P less than 0.001). Magnesium concentrations did not significantly change with flow although they were clearly different from zero: 0.12 +/- 0.02 vs. 0.10 +/- 0.02 mmole . liter-1. The rate of magnesium influx as a function of flow was also highly significant (r = 0.48, P less than 0.01). Thus, there is an increase in loop influx in all four ions with high flow rates despite disparate flow influences on early distal concentrations. In conclusion, these experiments demonstrate that (1) magnesium can enter the tubular lumen of the loop when this structure is perfused with a magnesium-free solution and (2) under our experimental conditions, phosphate can also enter the lumen suggesting that the concentration of phosphate at the early distal site is limited by the rate of entry.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D007684:Kidney Tubules / Q000378:metabolism*; D008138:Loop of Henle / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D010758:Phosphorus / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D007473:Ion Channels; D010758:Phosphorus; D008274:Magnesium; D011188:Potassium; D002118:Calcium