Summary
Microperfusion experiments on the proximal convolution of the rat kidney in situ led to the following observations:
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1.
The concentration of Ca++ in tubular fluid at which the net flux of Ca++ is zero is about 2.66 mEq/L. This corresponds to a TF/P of 0.78, very similar to the equilibrium Na+ TF/P of 0.76. The active pump potential for Ca++ under these conditions is E Ca ++=3 mV.
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2.
The rate of Ca++ reabsorption in the proximal convolution varies linearly with concentration up to a tubular fluid concentration of 15 mEq/L. Parathyroid hormone deficiency or excess has no influence on Ca++ reabsorption in the proximal convolution.
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3.
The ratio of net outward transport rates of Na+ and Ca++ at a TF/P of 1, is the same as the ratio of the concentrations of these ions in tubular fluid.
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4.
The ratio of net influxes of Na+ and Ca++ into Na+-free and Ca++-free perfusion solutions is the same as the ratio of the plasma concentrations of these ions.
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5.
Because of the striking similarities in the transport characteristics of Na+ and Ca++, it is postulated that similar or identical mechanisms are involved in the transtubular transport of the two ions.
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Supported by NIH-Grant AM 06806-03 and the Deutsche Forschungsgemeinschaft.
Established Investigator, American Heart Association, and Markle Scholar in Academic Medicine. Present address: Department of Medicine, University of North Carolina, School of Medicine, Chapel Hill, N.C.
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Frick, A., Rumrich, G., Ullrich, K.J. et al. Microperfusion study of calcium transport in the proximal tubule of the rat kidney. Pflügers Archiv 286, 109–117 (1965). https://doi.org/10.1007/BF00363855
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DOI: https://doi.org/10.1007/BF00363855