抄録
A release of cyclic AMP into the bathing medium from the urinary bladder of the toad, Bufo marinus was studied.
Appropriate pieces of the bladder were incubated in 3ml of bicarbonated Ringer's solution for 15 to 60 minutes under different conditions and then the amount of cyclic AMP in the medium and the dry tissue weight of the pieces were measured. The release of the nucleotide was expressed as pmoles/100 mg·dry tissue weight.
Even in the absence of arginine vasopressin (AVP) slight amount of cyclic AMP was found to be released from the tissue predominantly to the serosal medium. During exposure to AVP dose-dependent increases in the release of the nucleotide from the epithelial cells were observed. The maximum effect of 75mU/ml AVP on the release and on the cell level of cyclic AMP appeared nearly 30 minutes after commencement and continued up to one hour.
The release with 75mU/ml AVP was unaffected by 10 mM theophylline, although the cell level showed a further elevation. The recovery of radioactive cyclic AMP added to the bathing medium was also studied under the same conditions. Theophylline was found not to diminish the recovery, suggesting that the agent did not enhance any break-down of cyclic AMP in the medium. These results indicate that theophylline may inhibit the permeation of the nucleotide through the serosal membrane of the epithelial cell into the bathing medium.
Sodium fluoride is known to be a potent stimulator of the activity of adenyl cyclase of cell particle fractions. However, in any in tact cells or tissues the stimulation by sodium fluoride alone has not been reported. In this study a striking elevation of the intracellular cyclic AMP level of the whole cell system, the. intact urinary bladder, was observed with 10 mM sodium fluoride even in the absence of theophylline. This effect exceeded that of 75mU/ml AVP and was accompanied with a simultaneous increase in the release of cyclic AMP and with an increased permeability to water across the membrane of the bladder. These facts suggest that sodium fluoride stimulates the activity of adenyl cyclase even as with the whole cell system.
In brief the epithelial cells of the bladder always release cyclic AMP into the bathing medium predominantly to the serosal side and this release is enhanced by vasopressin and sodium fluoride, but is inhibited by theophylline. It is generally accepted that intracellular concentration of cyclic AMP is determined by the activities of adenyl cyclase and phosphodiesterase. In this study the third determinant, that is, the extent of the release of the nucleotide from the cell was proposed. Some regulatory mechanism for the third process with unknown intrinsic substances should be investigated.
