Single-channel biophysical and pharmacological characterizations of native human large-conductance calcium-activated potassium channels in freshly isolated detrusor smooth muscle cells

Recent studies have demonstrated the importance of large-conductance Ca2+-activated K+ (BK) channels in detrusor smooth muscle (DSM) function in vitro and in vivo. However, in-depth characterization of human native DSM single BK channels has not yet been provided. Here, we conducted single-channel recordings from excised patches from native human DSM cells. Inside-out and outside-out recordings in high K+ symmetrical solution (containing 140 mM KCl and ~300 nM free Ca2+) showed single-channel conductance of 215–220 pS, half-maximum constant for activation of ~+75 to +80 mV, and low probability of opening (Po) at +20 mV that increased ~10-fold at +40 mV and ~60-fold at +60 mV. Using the inside-out configuration at +30 mV, reduction of intracellular [Ca2+] from ~300 nM to Ca2+-free decreased the Po by ~85 %, whereas elevation to ~800 nM increased Po by ~50-fold. The BK channel activator NS1619 (10 μM) enhanced the Po by ~10-fold at +30 mV; subsequent application of the selective BK channel inhibitor paxilline (500 nM) blocked the activity. Changes in intracellular [Ca2+] or the addition of NS1619 did not significantly alter the current amplitude or single-channel conductance. This is the first report to provide biophysical and pharmacological profiles of native human DSM single BK channels highlighting their importance in regulating human DSM excitability.