Regulation of cAMP production in initial and terminal inner medullary collecting ducts

Regulation of cAMP production in initial and terminal inner medullary collecting ducts.

Background

The inner medullary collecting duct (IMCD) is composed of at least two functionally and morphologically distinct segments, the initial (IMCDi) and the terminal (IMCDt) portions. However, most studies of receptor signaling have been performed on cells obtained from the entire inner medulla. The purpose of this study was to determine whether the patterns of receptor-activated cAMP accumulation were different between these segments.

Methods

We measured cAMP accumulation stimulated by vasopressin and isoproterenol, and the effect of epinephrine in freshly dissected IMCDi and IMCDt segments cultured and IMCDi and IMCDt cells in primary culture.

Results

The maximum response to vasopressin was twofold higher in fresh IMCDt versus IMCDi (P < 0.05), however, it increased in cultured IMCDi by 40% versus fresh cells with no change in the response in fresh versus cultured IMCDt. The maximum response to isoproterenol was small in fresh cells but increased by five- and sixfold, respectively, in cultured IMCDi and IMCDt cells. α₂-Adrenoceptor stimulation almost completely inhibited both vasopressin and isoproterenol-stimulated cAMP accumulations in fresh IMCDi and IMCDt cells, but only partially inhibited either accumulation by 34 to 49% in cultured cells.

Conclusions

(1) IMCDi and IMCDt cells are both subject to vasopressin and α₂- and β-adrenergic regulation of adenylyl cyclase activity; (2) the relative influence of β-adrenergic, α₂-adrenergic and V₂ receptors to affect cAMP accumulation is altered in primary culture versus freshly dissected IMCD segments, suggesting that caution must be exercised in the extrapolation of data from cultured IMCD cells to in vivo models.