AJP - Regulatory, Integrative and Comparative Physiology, Vol 272, Issue 1 134-R141, Copyright © 1997 by American Physiological Society

ARTICLES

Posttranscriptional mechanisms regulate ontogenic changes in rat renal sodium-phosphate transporter

S. Taufiq, J. F. Collins and F. K. Ghishan
Department of Pediatrics, Steele Memorial Children's Research Center, University of Arizona Health Sciences Center, Tucson 85724, USA.

The present investigation sought to characterize the relationship between ontogeny and Na(+)-P(i) transporter expression in the rat kidney. Results showed that the maximal reaction rate (nmol.mg protein-1.10 s-1) of Na(+)-P(i) transport was highest in 21-day-old rats (2.26 +/- 0.26), was lower in 42- to 45-day-old rats (1.44 +/- 0.19) and 4-mo-old rats (0.78 +/- 0.15), and was lowest in 14-day-old rats (0.50 +/- 0.16) (P = 0.0009, n = 3). The Michaelis constants (mM Pi) were not significantly different in the four age groups. Northern blot analysis revealed that the abundance of Na(+)-P(i) transporter mRNA was similar in all four age groups (n = 5). Western blot analysis demonstrated the highest immunoreactive protein signal in the 21-day-old rat (Na(+)-P(i)/beta-actin = 4.15 +/- 1.16), followed by decreasing protein levels in 42-day-old rats (2.13 +/- 0.22), 4-mo-old rats (0.85 +/- 0.25), and 14-day-old rats (0.75 +/- 0.37) (P = 0.022, n = 5). Immunohistochemical analysis of kidney cortex in the four age groups showed specific staining of only apical membranes in all samples. We conclude that posttranscriptional mechanisms play a role in regulating this transporter during rat ontogeny.

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