Submitted on September 6, 2005
Accepted on January 30, 2006
The hydro-osmotic response of frog urinary bladder to serosal hypertonicity is dependent on adenylate cyclase for its maintenance and affected by [Cl-]o changes
Ann T Hanna-Mitchell1 and Elizabeth M Gebruers1*
1 Department of Physiology, University College Cork, Cork, Ireland
* To whom correspondence should be addressed. E-mail: e.gebruers{at}ucc.ie.
The role of adenylate cyclase (AC) in the maintenance of the hydro-osmotic response to serosal hypertonicity (SH) in anuran urinary bladder is disputed. In this study, norepinephrine (NE) significantly reversed the hydro-osmotic response of Rana temporaria bladders in hypertonic medium (330mOsm). The reversal was inhibited by yohimbine but was unaffected by prazosin and propranolol, indicating that NE action was mediated via 
2-adrenergic receptors. Pre-incubation of bladders with indomethacin did not interfere with the inhibitory action of NE, contra-indicating a role for prostaglandins. The SH hydro-osmotic response was abolished in the presence of 5 n-ethyl-N-isopropyl amiloride (EIPA) but the anti-diuretic hormone (ADH) hydro-osmotic response, was not. EIPA inhibits Na/H, known to be activated by cell shrinkage. An investigation of the anionic requirement of the SH hydro-osmotic response, revealed that replacement of bath chloride with the non-permeable anion, gluconate, reversibly abolished this response. In contrast, the hydro-osmotic response to ADH was unaffected by chloride removal; however when Cl- was absent, it was no longer augmented in hypertonic bath. The SH response was inhibited by the chloride channel blocker, 5-Nitro-2-(3-phenylpropylamino)-benzoate (NPPB) but not by the Na/K/2Cl inhibitor, bumetanide. Our results show that not only the onset but also the maintenance of the SH hydro-osmotic response is dependent on AC activity and does not differ in this respect to the ADH hydro-osmotic response. The effect of modifying [Cl-]o, suggests that this anion, possibly functionally linked with Na/H activity, may be involved in invoking the SH hydro-osmotic response in anuran urinary bladder.
