Does the gradual hydroosmotic response to antidiuretic hormone depend on intracellular cAMP accumulation or on the formation of intramembrane particle aggregates?

Abstract

In experiments on frog urinary bladder the mechanisms behind the gradual development of a hydroosmotic reaction to antidiuretic hormone (ADH) were investigated. It was suggested that the velocity of hydroosmotic reaction may be limited by (a) formation and insertion of particle aggregates into the apical membrane or (b) by velocity of cAMP formation. The urinary bladders were exposed to 23 nM ADH for different times (from 1 to 20 min) and water flow was measured over a period of 40 min. It was found that the value of the full hydroosmotic response increased progressively with the time of exposure to the hormone; however, the enhancement of water flow was equal during each time interval before reaching the reaction maximum. A direct correlation between the value of ADH-stimulated water flow, cAMP content in bladder tissue and frequency of particle aggregates in the granular cell apical membrane was observed. The content of cAMP in ADH-treated bladders was higher by 80% in the absence than in the presence of an osmotic gradient. Pretreatment of urinary bladders with 50 microM cyclic nucleotide phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, significantly accelerated the development of the hydroosmotic reaction and increased the magnitude of water flow in comparison with the effect of ADH only. No changes in cyclic AMP phosphodiesterase activity were found in the urinary bladder homogenates under the action of ADH, so it seems likely that accumulation of cAMP depends only on the increase of adenylate cyclase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Colonization of frog Rana temporaria L. urinary bladder by Gram‐negative bacteria leads to decreased effect of arginine‐vasotocin on water reabsorption from the urinary bladder

“…It is well known that in amphibian urinary bladder AVT‐induced insertion of aquaporins into the apical membrane of epithelial cell and increase of OWP strongly depends on accumulation of cAMP (Orloff and Handler, ; Natochin et al, ; Hasegawa et al, ). To clarify steps in AVT signaling pathway sensitive to LPS inhibition, we studied the influence of LPS treatment on OWP induced by forskolin, an activator of adenylate cyclase, and by IBMX, an inhibitor of cAMP‐specific phosphodiesterases.…”

“…Therefore, the urinary bladder, in concert with the skin and the kidney, are important for the maintenance of water balance (Jorgensen, ; Bentley, ). Water reabsorption through bladder epithelium is under the control of arginine‐vasotocin (AVT) (Bentley, ; Hays and Leaf, ; Finkelstein, ; Uchiyama and Konno, ), an amphibian antidiuretic hormone (ADH), involving similar molecular mechanisms to ADH‐induced water reabsorption in the distal portion of the mammalian nephron (Orloff and Handler, ; Sasaki et al, ; Natochin et al, ; Hasegawa et al, ; Suzuki et al, ). For this reason, the urinary bladder of anuran amphibians has been widely used as a model for studying the molecular mechanisms of osmotic water permeability (OWP) regulation in tight epithelia.…”

Effects of vasopressin on hyaluronate hydrolase activities and water permeability in the frog urinary bladder

“…It is established that an increase in cAMP content in urinary bladder tissue is also directly related to changes in intramembrane particle number and to the rise in water permeability caused by AVP [21,30]. Intramembrane particle aggregates have been regarded as a water channel system [30].…”

“…Arginine vasopressin (AVP, 50 nM, Sigma), forskolin (30 µM, Sigma), l-desamino-8-D-arginine-vasopressin (dDAVP, Adiuretin-SD, Spofa CSSR, 1.5 µM), and cytochalasin B (50 nM, Sigma) were added to the serosal Ringer solution. Water flow was measured gravimetrically in each hemibladder at 30-min intervals by Bentley's modified method [21]. Each hemibladder sac was allowed to equilibrate for 30 min in Ringer solution, then different drugs were added.…”