Noradrenaline inhibits pacemaker currents through stimulation of β₁‐adrenoceptors in cultured interstitial cells of Cajal from murine small intestine

Abstract

1 Interstitial cells of Cajal (ICCs) are pacemaker cells that activate the periodic spontaneous inward currents (pacemaker currents) responsible for the production of slow waves in gastrointestinal smooth muscle. The effects of noradrenaline on the pacemaker currents in cultured ICCs from murine small intestine were investigated by using whole-cell patch-clamp techniques at 301C. 2 Under current clamping, ICCs had a mean resting membrane potential of À5875 mV and produced electrical slow waves. Under voltage clamping, ICCs produced pacemaker currents with a mean amplitude of À410757 pA and a mean frequency of 1672 cycles min À1 . 3 Under voltage clamping, noradrenaline inhibited the amplitude and frequency of pacemaker currents and increased resting currents in the outward direction in a dose-dependent manner. These effects were reduced by intracellular GDPbS. 4 Noradrenaline-induced effects were blocked by propranolol (b-adrenoceptor antagonist). However, neither prazosin (a 1 -adrenoceptor antagonist) nor yohimbine (a 2 -adrenoceptor antagonist) blocked the noradrenaline-induced effects. Phenylephrine (a 1 -adrenoceptor agonist) had no effect on the pacemaker currents, whereas isoprenaline (b-adrenoceptor agonist) mimicked the effect of noradrenaline. Atenolol (b 1 -adrenoceptor antagonist) blocked the noradrenaline-induced effects, but butoxamine (b 2 -adrenoceptor antagonist) did not. In addition, BRL37344 (b 3 -adrenoceptor agonist) had no effect on pacemaker currents. 5 9-(Tetrahydro-2-furanyl)-9H-purine-6-amine (SQ-22536; adenylate cyclase inhibitor) and a myristoylated protein kinase A inhibitor did not inhibit the noradrenaline-induced effects and 8-bromo-cAMP had no effects on pacemaker currents. 8-Bromo-cGMP and SNAP inhibited pacemaker currents and these effects of SNAP were blocked by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; a guanylate cyclase inhibitor). However, ODQ did not block the noradrenaline-induced effects. 6 Neither tetraethylammonium (a voltage-dependent K þ channel blocker), apamin (a Ca 2 þ -dependent K þ channel blocker) nor glibenclamide (an ATP-sensitive K þ channel blocker) blocked the noradrenaline-induced effects. 7 The results suggest that noradrenaline-induced stimulation of b 1 -adrenoceptors in the ICCs inhibits pacemaker currents, and that this is mediated by the activation of G-protein. Neither adenylate cyclase, guanylate cyclase nor a K þ channel-dependent pathway are involved in this effect of noradrenaline.

Activating of ATP-Dependent K⁺ Channels Comprised of K_ir 6.2 and SUR 2B by PGE₂ Through EP₂ Receptor in Cultured Interstitial Cells of Cajal from Murine Small Intestine

“…Namely, in ICC, the generation of pacemaker currents and the regulation of ATP-sensitive K + channels on this may involve the cAMP signaling. However, in a recent study and figure 5B, the treatment 8-bromo-cAMP (a cell-permeable cAMP analog) in ICC had no effects on pacemaker currents [48]. Also, pretreatment with SQ-22536, an adenylate cyclase inhibitor, does not influence PGE 2 actions on pacemaker currents, and in a cAMP assay, PGE 2 did not stimulated the production of cAMP.…”

Phentolamine inhibits the pacemaker activity of mouse interstitial cells of Cajal by activating ATP-sensitive K+ channels

“…We previously reported that β-adrenoceptor activation modulates pacemaker activity in cultured mouse intestinal ICC (Jun et al, 2004) suggesting that phentolamine exhibits activity on the pacemaker activity of ICC. We have also observed that phentolamine inhibits ICC pacemaker activity as per our preliminary result.…”

Muscarinic Regulation of Ether-a-go-go-Related Gene K+ Currents in Interstitial Cells of Cajal

“…Recently, two studies have addressed the question of whether or not neurotransmitters directly regulate pacemaker currents in ICC. In isolated ICC of the murine small intestine, noradrenaline modulates pacemaker currents by decreasing pacemaker frequency (Jun et al, 2004). In ICC of the murine stomach, acetylcholine increased pacemaker frequency (Kim et al, 2003).…”