Calcium dependent K-channels in guinea pig and human urinary bladder.

This study provides evidence for the presence of large conductance Ca(2+)-dependent K-channels in guinea pig and human urinary bladder smooth muscle. A23187, a Ca(2+)-ionophore, increased charybdotoxin and iberiatoxin sensitive 42K efflux in human urinary bladder smooth muscle cells, suggesting that large conductance Ca(2+)-dependent K-channels are present in these cells. NS004, a large conductance Ca(2+)-dependent K-channel opener, relaxed guinea pig bladder strips precontracted with 15 mM KCl which is inhibited by iberiatoxin. In addition, NS004 also evoked an iberiatoxin sensitive increase in 86Rb/42K efflux in guinea pig and human urinary bladder smooth muscle cells, demonstrating that NS004 activates large conductance Ca(2+)-dependent K-channels to achieve its relaxation effect in the bladder.

K-channel opening activity of ZD6169 and its analogs: effect on 86Rb efflux and 3H-P1075 binding in bladder smooth muscle.

Zeneca ZD6169, (S)-N-(4-benzoylphenyl)-3,3,3-trifluoro- 2-hydroxy-2-methylpropionamide, is a novel compound which relaxes urinary bladder smooth muscle in vitro. The effect of ZD6169 and two of its analogs on 86Rb efflux and 3H-P1075 binding in guinea pig bladder strips was investigated to characterize the K-channel opening properties of this compound. ZD6169 concentration dependently increased the rate of 86Rb efflux from guinea pig bladder strips. 86Rb efflux evoked by ZD6169 and its analogs was blocked by glibenclamide (30 muM) but not by charybdotoxin, apamin or alpha-dendrotoxin, suggesting that this compound activates KATP channels in guinea pig bladder. In addition, interaction of ZD6169 with KATP channels was also confirmed in human bladder smooth muscle cells. Specific binding of 3H-P1075, a potent opener of KATP channels, to guinea pig urinary bladder strips was observed. 3H-P1075 binding was inhibited by known KATP openers. ZD6169 inhibited binding of 3H-P1075 to urinary bladder strips like other structurally different KATP openers, e.g. cromakalim and pinacidil. Potencies for inhibition of 3H-P1075 binding by ZD6169 and other potassium channel openers correlate well with potencies for increase in 86Rb efflux and bladder muscle relaxation studies. It is concluded that Zeneca ZD6169 is a potassium channel opener which activates ATP-sensitive K-channels in guinea pig urinary bladder strips as well as in human bladder cells. Furthermore, binding studies suggest that the effects of ZD6169 and its analogs are mediated by binding to the site labeled by 3H-P1075 in guinea pig bladder strips.

K-channel opening activity of dihydropyridine ZM244085: effect on 86Rb efflux and 3H-P1075 binding in urinary bladder smooth muscle.

Zeneca ZM244085, 9-(3 cyanophenyl)hexahydro-1,8 acridinedione, is a novel dihydropyridine (DHP) which relaxes KCl precontracted urinary bladder smooth muscle in vitro. The effect of ZM244085 on low and high KCl induced contractions, 86Rb efflux and [3H]-P1075 binding in guinea pig bladder strips was investigated to characterize the K-channel opening properties of this compound. Since ZM244085 is a dihydropyridine its effect on DHP binding sites on Ca2+ channels was also investigated. ZM244085 was found to be more potent in relaxing detrusor strips precontracted with 15 mM KCl than strips precontracted with 80 mM KCl (Li et al., 1995). This functional profile of ZM244085 is similar to that exhibited by typical K-channel openers (PCO). In addition, inhibition of ZM244085 induced relaxation of detrusor strips by glibenclamide suggests that ZM244085 opens ATP sensitive K-channel (KATP) in urinary bladder (Li et al., 1995). Since the glibenclamide sensitive smooth muscle relaxation activity of ZM244085 could still be an indirect effect of this compound on KATP channels we carried out 86Rb efflux studies and [3H]-P1075 binding studies to further confirm these findings. The 86Rb efflux assay is a direct method for monitoring the movement of K+ ions across the cell membranes. Displacement of [3H]-P1075 binding to bladder membranes supports a direct action of the compound on the KATP channel. The present study demonstrates that ZM244085 in a concentration dependent manner increases the rate of 86Rb efflux from guinea pig bladder strips. This effect was inhibited by glibenclamide (30 microM), a known KATP channel blocker. In addition, interaction of ZM244085 with KATP channels was also confirmed in human bladder smooth muscle cells using a 42K efflux assay. Furthermore, we were able to demonstrate that ZM244085, structurally distinct PCO, inhibited the binding of 3H-P1075 to urinary bladder strips in a manner similar to other KATP openers such as cromakalim and pinacidil. Inhibition of 3H-P1075 binding by ZM244085 and other PCO's correlates well with increases in 86Rb efflux and bladder muscle relaxation studies. Finally, ZM244085 did not exhibit any significant affect on VSCC as evidenced by very weak inhibition of [3H]-PN200,110 binding to bladder membranes by ZM244085. It is concluded that Zeneca ZM244085 is a PCO which activates KATP channels in urinary bladder.