Effects of Alterations in Potassium and Calcium Concentrations on the Pressure Generated in Rat Whole Bladder In Vitro

Background: Various physiologic systems maintain the ionic equilibrium essential tor normal neuron and smooth muscle function. These systems are impaired by nonphysiologic concentrations of extracellular cations. This study investigated the effects of altered extracellular concentrations of potassium and calcium on the in vitro pressure generation in the whole bladder of rats.
Methods: Pressure increases in response to field stimulation, as well as low and high doses of bethanechol, were determined in a Krebs solution containing a normal amount of potassium, and in excess of 10mmol/L and 20mmol/L of potassium. Each of these solutions had calcium concentrations, that were low (0.8mmol/L), normal (2.5mmol/L), or high (7.5mmol/L).
Results: The response to field stimulation was significantly decreased at the 20-mmol/L concentration of potassium in the presence of the different concentrations of calcium. The response to field stimulation increased as the extracellular concentration of calcium increased. The pressure increase caused by a low dose of bethanechol was significantly enhanced by elevations in the concentrations of both potassium and calcium. There was no difference in the response to a high dose of bethanechol in the presence of the various concentrations of potassium and calcium.
Conclusion: These findings indicated that changes in the cationic equilibrium that result in blocking of the neuronal sodium channels, as well as increasing the level of intracellular bound calcium in smooth muscle, alter bladder function in vitro.