A description of Ca2+ channels in human detrusor smooth muscle
Article first published online: 21 AUG 2003
Volume 92, Issue 4, pages 476–482, September 2003
How to Cite
Sui, G.P., Wu, C. and Fry, C.H. (2003), A description of Ca2+ channels in human detrusor smooth muscle. BJU International, 92: 476–482. doi: 10.1046/j.1464-410X.2003.04356.x
- Issue published online: 21 AUG 2003
- Article first published online: 21 AUG 2003
- Accepted for publication 31 March 2003
- human detrusor;
- Ca2+ channels;
- membrane potential;
- spontaneous depolarization
To characterize the Ca2+ channels in human detrusor smooth muscle and to investigate their contribution to spontaneous electrical activity.
MATERIALS AND METHODS
Isolated human detrusor smooth muscle myocytes were used to measure ionic currents under voltage-clamp or membrane potential under current-clamp. Membrane potential oscillations were analysed in terms of oscillation frequency and amplitude using fast Fourier transforms.
Under voltage-clamp an inward current dependent on extracellular Ca2+ was recorded using Cs+-filled patch electrodes. The current could be separated into two components on the basis of their sensitivity to Ni2+, verapamil or nicardipine, and their dependence on holding and clamp potential. A Ni2+-sensitive component activated over a relatively negative range of potentials (−60 to −20 mV) comprised about a third of the total current and was designated a T-type Ca2+ current. A verapamil/nicardipine-sensitive component, activated at more positive potentials, was designated an l-type Ca2+ current. Using K+-based filling solutions spontaneous transient outward currents were recorded that had the characteristics of current flow through BK channels. Membrane potential oscillations, under current-clamp increased in frequency but not amplitude as the mean membrane potential was made less negative. The voltage-dependence of oscillation frequency was similar to that of the l-type, but not T-type, Ca2+ current activation curve. Furthermore oscillation frequency was slowed by verapamil but not Ni2+.
The study showed, for the first time, the presence of both T- and L-type Ca2+ channels in human detrusor smooth muscle; we propose a role for these channels in spontaneous activity. The results suggest that the L-type Ca2+ current can control membrane potential oscillation frequency. The significance of this finding for spontaneous contractions is discussed.