High Activity of Low-Michaelis-Menten Constant 3',5'-Cyclic Adenosine Monophosphate-Phosphodiesterase Isozymes in Renal Inner Medulla of Mice With Hereditary Nephrogenic Diabetes Insipidus
| Title: | High Activity of Low-Michaelis-Menten Constant 3',5'-Cyclic Adenosine Monophosphate-Phosphodiesterase Isozymes in Renal Inner Medulla of Mice With Hereditary Nephrogenic Diabetes Insipidus |
|---|---|
| Authors: | Takeda, Shigeyuki; Lin, Chiann-Trzuo; Morgano, Paul G.; McIntyre, Steven; Dousa, Thomas P. |
| Publisher: | Endocrinology |
| Date Published: | July 01, 1991 |
| Reference Number: | 321 |
Our previous studies on microdissected kidney tubule segments indicate that the failure of vasopressin (VP) to increase cAMP content in collecting ducts of mice with hereditary nephrogenic diabetes insipidus (NDI mice) is due to abnormally rapid cAMP catabolism via cyclic-3',5'-nucleotide phosphodiesterases (PDE). Furthermore, the VP-stimulated cAMP accumulation can be restored by addition of PDE isozyme-specific inhibitors. To elucidate the biochemical basis of the NDI syndrome, we analyzed PDE activities in extracts from inner medullary tissues of NDI mice and from control mice separated with the use of ionex fast protein liquid chromatography on a Mono-Q column. In extracts of inner medullary tissues from either control or NDI mice, the low Michaelis-Menten constant (Km) cAMP-PDE activity specific for cAMP as a substrate (cAMP-PDE) was eluted from a Mono-Q column with linear sodium acetate gradient as peak 3 at Na-acetate concentration (0.75-0.93 M) and was well separated from fractions containing the Ca(2+)-calmodulin sensitive PDE. The cAMP-PDE activity in peak 3 was significantly higher in NDI mice (greater than delta + 100%) than in controls. The sensitivity to effect of cAMP-PDE isozyme-specific inhibitors, rolipram and cilostamide, indicates that peak 3 consists predominantly (approximately 75%) of the rolipram-sensitive PDE-IV isozyme and a minor portion (approximately 25%) of cilostamide-sensitive PDE-III isozyme in both control and NDI mice. Higher activity of PDE-IV in NDI mice was due to 2.4 times higher apparent maximum velocity compared to controls, whereas the apparent Km for cAMP was not different. Our results show that low Km cAMP-PDE activities, predominantly PDE-IV, are higher in inner medulla of NDI mice. We suggest that the higher activity of PDE-IV, and to a lesser degree perhaps also PDE-III, accounts for rapid cAMP hydrolysis, which prevents the increase of cAMP generated in the response to VP in collecting ducts of NDI mice.
This translation by the NDI Foundation is to assist the lay reader. To provide a clear, accessible interpretation of the original article, we eliminated or simplified some technical detail and complicated scientific language. We concentrated our translation on those aspects of the article dealing directly with NDI. The NDI Foundation thanks the researchers for their work toward understanding and more effectively treating this disorder.
© Copyright NDI Foundation 2007 (JC)
Takeda, et al's. previous research indicated that the biochemical basis for nephrogenic diabetes insipidus (NDI) in a strain of mice with hereditary NDI is extremely rapid breakdown of cAMP. cAMP is decomposed through hydrolysis before it can perform its function in the molecular sequence that leads to water reabsorption and urine concentration.
In their research, the authors found the enzymes responsible for this too rapid decomposition were two isozymes of nucleotide phosphodiesterase (PDE): PDE-IV and PDE-III. PDE-IV had the primary effect in the decomposition of cAMP.
In this research project, Takeda, et al., further clarified the biochemical basis of NDI in NDI mice. To do so, they analyzed various PDE activities in extracts of the inner medullary tissues of NDI mice and the healthy mice that served as a control group. The inner medullary tissues contain the innermost portions of the kidney collecting duct.
The authors found the PDE activity was significantly higher in NDI mice than in the controls. More specifically, the authors found that PDE-IV activity is higher in the inner medulla of NDI mice. This study provides the initial evidence in support of the hypothesis that higher than normal PDE-IV and, to a significantly lower extent, PDE-III activity is responsible for the rapid breakdown of cAMP that prevents the kidney from reabsorbing water and concentrating urine in response to AVP.