Muscarinic receptors inhibit ATP-sensitive K+ channels in swine tracheal smooth muscle

Abstract

The patch-clamp technique was used to characterize a cromakalim-induced current and its regulation by muscarinic receptors in tracheal smooth muscle cells. Cromakalim (10 microM) activated a steady-state increase of 33-292 pA (91.2 +/- 8.8 pA, n = 43) in whole cell current, consistent with the activation of ATP-sensitive K+ (KATP) channels. Acetylcholine (10 nM-1 microM), added cumulatively, inhibited the cromakalim-induced current by 23.6 +/- 14.9 to 73.9 +/- 4.6%. This inhibition was blocked by pretreatment with atropine (1 microM). The cromakalim-induced current was also inhibited 83.0 +/- 8.3% by phorbol 12-myristate 13-acetate (100 nM, n = 6). The inhibition of the cromakalim-induced current by acetylcholine (1 microM) and phorbol 12-myristate 13-acetate (100 nM) was reduced to 27.3 +/- 3.1% (n = 10) and 32.8 +/- 7.8% (n = 3), respectively, in the presence of staurosporine (100 microM). We conclude that muscarinic receptor stimulation inhibits KATP channel activity through the activation of protein kinase C. These findings suggest that KATP channels may play a role in the regulation of membrane potential and contractility in airway smooth muscle.

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

“…In swine tracheal myocytes, Nuttle & Farley (1997) have described a (±)‐cromakalim‐induced K + current which was inhibited by intracellular ATP (i.e. K ATP current).…”

“…In airway smooth muscle, since glibenclamide selectively inhibits not only the membrane hyperpolarization ( Murray et al ., 1989 ), but also the K + ( 86 Rb + ) efflux ( Allen et al ., 1986 ) and the muscle relaxation induced by K + channel openers (guinea‐pig, Arch et al ., 1988 ; human, Black et al ., 1990 ), it is generally believed that glibenclamide‐sensitive K + channels are the target channels for K + channel openers. Recently, Nuttle & Farley (1997) have reported that in swine cultured tracheal smooth muscle cells, (±)‐cromakalim‐induced glibenclamide‐sensitive membrane currents are inhibited by protein kinase C through muscarinic receptors. However, there has been no direct report concerning the electrophysiological and pharmacological properties of the glibenclamide‐sensitive K + channels in tracheal myocytes by use of single‐channel recordings.…”

Protein kinase C isoenzymes: a review of their structure, regulation and role in regulating airways smooth muscle tone and mitogenesis

“…Path clamp studies using porcine tracheal smooth muscle cells have established that ACh and PMA inhibit the activation of ATP‐sensitive K + channels (K ATP ) in response to levcromakalim ( Nuttle & Farley, 1997 ) implying that a cPKC or nPKC is responsible. Staurosporine antagonized the effect of both ACh and PMA from which the authors suggest that activation of the muscarinic receptor on porcine trachealis inhibits K ATP by a PKC‐dependent mechanism.…”

ATP-Sensitive Potassium Channels

“…There have been few studies addressing the physiological role of K ATP channels in airway smooth muscle, though muscarinic stimulation inhibited K ATP current via PKC in swine tracheal muscle cells, consistent with a role in membrane potential and airway contractility [191]. However, a variety of synthetic K ATP channel openers are effective in relaxing airway smooth muscle in vivo as well as in vitro, indicating the presence of significant populations of K ATP channels [76].…”