= Mark A. Knepper
{c}
<Mark A. Knepper> is a researcher in <kidney> <physiology> who uses <systems biology> to investigate the regulation of water transport. A central example is how <vasopressin> changes the distribution of <aquaporin-2> between the <plasma membrane> and the interior of <collecting duct> <cells>. His 2010 research report describes combining <mass spectrometry>, measurements of <gene expression>, mathematical modeling and physiological experiments to investigate this regulation.<Solute And Water Transport In Renal Epithelia by Mark A. Knepper>[NIH RePORTER project 1ZIAHL001285-24, fiscal year 2010; Abstract]{ref}
The timing gives the mechanism its interest. On a scale of seconds to minutes, <membrane trafficking> can move existing <aquaporin-2> into the <plasma membrane>, changing the route available for water movement. That is a different regulatory step from making additional <aquaporin-2> through altered <gene expression>. Measuring how much channel <protein> exists and where it is located therefore answers different questions.<Solute And Water Transport In Renal Epithelia by Mark A. Knepper>[Abstract: rapid redistribution between membrane and cytoplasm]{ref}
<Mark A. Knepper> also wrote a scientific remembrance of <Maurice B. Burg>, explaining how experiments on isolated <renal tubules> opened individual transport mechanisms to direct investigation.<Maurice B. Burg (1931–2022), discoverer of kidney transport mechanisms by Mark A. Knepper>[Opening and discussion of the isolated-perfused-tubule method; PNAS 119, e2209749119, 2022]{ref}
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