KCNQ Currents and Their Contribution to Resting Membrane Potential and the Excitability of Interstitial Cells of Cajal From the Guinea Pig Bladder

Abstract

Purpose: The presence of novel KCNQ currents was investigated in guinea pig bladder interstitial cells of Cajal and their contribution to the maintenance of the resting membrane potential was assessed. Materials and Methods: Enzymatically dispersed interstitial cells of Cajal were patch clamped with K⁺ filled pipettes in voltage clamp and current clamp modes. Pharmacological modulators of KCNQ channels were tested on membrane currents and the resting membrane potential. Results: Cells were stepped from −60 to 40 mV to evoke voltage dependent currents using a modified K⁺ pipette solution containing ethylene glycol tetraacetic acid (5 mM) and adenosine triphosphate (3 mM) to eliminate large conductance Ca activated K channel and K_{adenosine triphosphate} currents. Application of the KCNQ blockers XE991, linopirdine (Tocris Bioscience, Ellisville, Missouri) and chromanol 293B (Sigma®) decreased the outward current in concentration dependent fashion. The current-voltage relationship of XE991 sensitive current revealed a voltage dependent, outwardly rectifying current that activated positive to −60 mV and showed little inactivation. The KCNQ openers flupirtine and meclofenamic acid (Sigma) increased outward currents across the voltage range. In current clamp mode XE991 or chromanol 293B decreased interstitial cell of Cajal resting membrane potential and elicited the firing of spontaneous transient depolarizations in otherwise quiescent cells. Flupirtine or meclofenamic acid hyperpolarized interstitial cells of Cajal and inhibited any spontaneous electrical activity. Conclusions: This study provides electrophysiological evidence that bladder interstitial cells of Cajal have KCNQ currents with a role in the regulation of interstitial cell of Cajal resting membrane potential and excitability. These novel findings provide key information on the ion channels present in bladder interstitial cells of Cajal and they may indicate relevant targets for the development of new therapies for bladder instability.