Properties and pharmacological modification of ATP‐sensitive K⁺ channels in cat tracheal myocytes

Abstract

1 The e ects of levcromakalim and nucleoside diphosphates (NDPs) on both membrane currents and unitary currents in cat trachea myocytes were investigated by use of patch-clamp techniques. 2 In conventional whole-cell con®guration, levcromakalim produced a concentration-dependent K + current which was suppressed by additional application of 5 mM glibenclamide at 770 mV. When 3 mM ATP was added in the pipette solution, the peak amplitude of the levcromakaliminduced current was much smaller than that in the absence of ATP. 3 When 3 mM uridine 5'-diphosphate (UDP) was included in the pipette solution, much higher concentrations of glibenclamide (550 mM) were required to suppress the 100 mM levcromakaliminduced membrane current in comparison with those in the absence of UDP. 4 In the cell-attached patches, levcromakalim activated a 40 pS K + channel which was inhibited by additional application of glibenclamide in symmetrical 140 mM K + conditions. 5 UDP (50.1 mM) was capable of reactivating the channel in inside-out patches in which the glibenclamide-sensitive K + channel had run down, in the presence of levcromakalim. The K + channel reactivated by UDP was suppressed by additional application of either intracellular 3 mM ATP or 100 mM glibenclamide. 6 These results demonstrate that smooth muscle cells in the cat trachea possess ATP-sensitive 40 pS K + channels which are blocked by glibenclamide (i.e. K ATP ) and can be activated by levcromakalim and that intracellular UDP causes a signi®cant shift of the glibenclamide-sensitivity of these channels.

Modification of ATP-sensitive K+ channels by proteolysis in smooth muscle cells from pig urethra

“…The data recording system used was essentially the same as that described previously (Teramoto et al, 2000a). In short, generation of voltage pulses was performed using a L/M-EPC 8 patch-clamp ampli®er (HEKA Elektronik Corp., Lambrecht, Germany) in conjunction with a circuit board which has both an analogue to digital and a digital to analogue conversion function (ITC-16, Instrutech Corp., NY, U.S.A.), using a`Pulse' software package (HEKA Elektronik Corp., Lambrecht, Germany).…”

“…Patch-clamp experiments were performed at room temperature (21 ± 238C) as described previously (Teramoto et al, 2000a). Junction potentials between bath and pipette solutions were measured with a 3 M KCl reference electrode and were 52 mV, so that correction for these potentials was not made.…”

The effects of flecainide on ATP‐sensitive K+ channels in pig urethral myocytes

“…Patch‐clamp experiments were performed at room temperature (21–23°C) as described previously ( Teramoto et al ., 2000a , 2000b ). Junction potentials between bath and pipette solutions were measured with a 3 M KCl reference electrode and were <2 mV, so that correction for these potentials was not made.…”

“…The data recording system used was essentially the same as that described previously ( Teramoto et al ., 2000a , 2000b ). In short, generation of voltage pulses was performed using a L/M‐EPC 8 patch‐clamp amplifier (HEKA Elektronik Corp., Lambrecht, Germany) in conjunction with a circuit board which has both an analogue to digital and a digital to analogue conversion function (ITC‐16, Instrutech Corp., NY, U.S.A.), using a ‘Pulse’ software package (HEKA Elektronik Corp., Lambrecht, Germany).…”

ATP-Sensitive Potassium Channels

“…A more recent study in tracheal smooth muscle has demonstrated ATP-sensitive currents activated by levcromakalim and corresponding single channels with a conductance of 40 pS. Uridine diphosphate reactivated these channels after rundown [192]. K ATP channel openers have potential for the treatment of airway hypercontractility [168].…”