The Effect of Extracellular Calcium on the Contractile Response to Field Stimulation, Bethanechol and ATP in Rabbit Urinary Bladder

Yoon, Jai Young; Kim, Joon Chul; Lee, Dong Whan; Hwang, Tae Kon; Park, Yong Hyun

Abstract

PURPOSE: In a previous study increasing the extracellular clacium concentration enhanced the phasic contractile response to low frequency stimulation(2Hz) to a significantly greater degree than the enhancement of high frequency stimulation(16Hz). To investigate the sensitivity of the detrusor contractile responses to field stimulation, bethanechol and ATP in calcium free buffer, the current study was designed.
MATERIALS AND METHODS
Each rabbit bladder strip of 5x10mm in size was incubated for 30 minutes in the Tyrode's solution. Individual strips were utilized to generate the response to field stimulation(2, 8 and 32Hz), bethanechol(1.0-250microM) or ATP(0.25-2mM). Upon completion of the first stimulation in Tyrode's solution, each tissue was washed 3 1.tomes at 15 minute intervals with fresh Tyrodes. At 15 minutes following the last wash, the Tyrode's solution was replaced with solution containing no calcium+1.0mM EGTA and incubated for ditional 5, 15 or 30 minutes. At the end of 5, 15 or 30-min period of tulibration a second round of field stimulation or dose-response curves to bethanechol or ATP were generated. The contractile responses were monitored via an FT03 force transducer and recorded on a Grass 7D polygraph and expressed as the g tension per 100mg of tissue.
RESULTS
(1) Progressive decrease in both basal tension and spontaneous contractile activity (2) more rapid decrease in the contractile response to 2 and 8Hz field stimulation than to 32Hz stimulation (3) more rapid decrease in the contractile response to lower concentrations of bethanechol and ATP than to high concentrations (4) greater maximal inhibition of the contractile response to low concentrations of bethanechol and ATP than to high concentrations.
CONCLUSIONS
These results indicated that detrusor contractility to a sub-maximal stimulation rather than maximal stimulation is more sensitive to extracellular calcium depletion.