Amphotericin B decreases adenylyl cyclase activity and aquaporin-2 expression in rat kidney

The present study was intended to examine whether the amphotericin-induced urinary concentration defect can be related to an altered regulation of aquaporin (AQP) water channels in the kidney. Male Sprague-Dawley rats were injected with amphotericin B (6 mg/kg/d, IP) for 21 days. The protein expression of AQP1-3, Gsa, and adenylyl cyclase was determined in the kidney. To further specify the primary point of dysregulation of AQP channels that are activated by the arginine vaso-pressin/cyclic adenosine monophosphate (AVP/cAMP) pathway, different components of adenylyl cyclase complex were separately examined for their cAMP-generating activities. Amphotericin treatment resulted in kidney failure associated with decreased tubular water reabsorption and increased urinary flow rate. The expression of AQP2 proteins was significantly decreased in the outer medulla and inner medulla but not in the cortex. The expression of AQP2 proteins in the membrane fraction changed in parallel with that in the cytoplasmic fraction, suggesting a preserved targeting. Neither the expression of AQP1 nor that of AQP3 was significantly affected in the cortex, outer medulla, or inner medulla. The cAMP generation in response to AVID or sodium fluoride was decreased, whereas that to forskolin was not significantly altered. The expression of Gs alpha proteins was decreased in the inner medulla, whereas that of adenylyl cyclase VI remained unaltered. These findings indicate that the amphotericin-induced urinary concentration defect may in part be causally related to a reduced abundance of AQP2 channels in the kidney. It is also suggested that the primary impairment in the pathway leading to the activation of AQP channels that are regulated by the AVP/cAMP pathway lies at the level of G proteins.