engleski

Expression of AQP1 in the Rat Kidney is Sex Dependent

AQP1 mediates a constitutive water permeability in the mammalian kidney. In the membrane, the functional protein exists in both nonglycosylated (NG, MM=28 kDa) and glycosylated (G, MM=40-60 kDa) forms. Factors that may influence the expression of AQP1 in physiological conditions are poorly known. To investigate possible sex differences, we compared the expression of AQP1 by immunocytochemistry in kidney tissue cryosections of adult male (M) and female (F) rats, and by immunoblotting in total cell membranes (TCM) isolated from the same tissue. Immunocytochemistry with serial dilutions of the polyclonal anti-AQP1 antibody revealed a higher intensity of the specific staining along the M nephron. By semiquantitative densitometry of the immunoblotting data (relative units+SEM ; n= 6 M and 6 F) in TCM from the kidney cortex (C), outer stripe (OS) and inner stripe&papilla (ISP) showed that the total abundance of AQP1 (NG+G) in M tissues (160+14.5, 167+11.1, and 162+12.7, respectively) was higher than in F tissues (123+5.4, 127+10.5, and 100+5.5, respectively ; vs. respective M data P<0.05). However, the density of NG form of AQP1 in TCM from C, OS and ISP varied from 74 to 89 relative units, and was not significantly different between M and F. The observed sex differences were clearly confined only to the G form of AQP1 ; the band density of the G form in the M C, OS and ISP was 77+8.6, 85+6.6, and 81+8.1, respectively, whereas comparable data in F tissues were 49+1.9, 39+5.3, and 23+4.6, respectively (vs. respective M data, P<0.01). Comparison of the M (n=26) and F (n=26) 24 h urine parameters showed a higher excretion of protein by M and no difference in urine phosphate, osmolality and flow. We conclude that the significant gender differences exist in the abundance of the total AQP1 and its G form along the rat nephron (M>F). These differences are not reflected in the ability of M and F kidney to excrete and concentrate the urine.

gender differences; immunocytochemistry; nephron; water channels

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