Noradrenaline inhibits pacemaker currents through stimulation of beta 1-adrenoceptors in cultured interstitial cells of Cajal from murine small intestine.
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 30 degrees C. 2. Under current clamping, ICCs had a mean resting membrane potential of -58+/-5 mV and produced electrical slow waves. Under voltage clamping, ICCs produced pacemaker currents with a mean amplitude of -410+/-57 pA and a mean frequency of 16+/-2 cycles min(-1). 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 GDP beta S. 4. Noradrenaline-induced effects were blocked by propranolol (beta-adrenoceptor antagonist). However, neither prazosin (alpha(1)-adrenoceptor antagonist) nor yohimbine (alpha(2)-adrenoceptor antagonist) blocked the noradrenaline-induced effects. Phenylephrine (alpha(1)-adrenoceptor agonist) had no effect on the pacemaker currents, whereas isoprenaline (beta-adrenoceptor agonist) mimicked the effect of noradrenaline. Atenolol (beta(1)-adrenoceptor antagonist) blocked the noradrenaline-induced effects, but butoxamine (beta(2)-adrenoceptor antagonist) did not. In addition, BRL37344 (beta(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(+) channel blocker), apamin (a Ca(2+)-dependent K(+) channel blocker) nor glibenclamide (an ATP-sensitive K(+) channel blocker) blocked the noradrenaline-induced effects. 7. The results suggest that noradrenaline-induced stimulation of beta(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(+) channel-dependent pathway are involved in this effect of noradrenaline.
Jun
Jae Yeoul
JY
Department of Physiology, College of Medicine, Chosun University, 375 Seosuk-dong, Gwangju 501-759, Korea.
Choi
Seok
S
Yeum
Cheol Ho
CH
Chang
In Youb
IY
Park
Chan Kuk
CK
Kim
Man Yoo
MY
Kong
In Deok
ID
So
Insuk
I
Kim
Ki Whan
KW
You
Ho Jin
HJ
D000067956:Adenylyl Cyclase Inhibitors; D058665:Adrenergic beta-1 Receptor Agonists; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology; D005769:Gastrointestinal Motility / Q000187:drug effects; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D007421:Intestine, Small / Q000166:cytology / Q000187:drug effects*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008807:Mice, Inbred BALB C; D009638:Norepinephrine / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology
D000067956:Adenylyl Cyclase Inhibitors; D058665:Adrenergic beta-1 Receptor Agonists; D004791:Enzyme Inhibitors; D026902:Potassium Channel Blockers; D019204:GTP-Binding Proteins; D006162:Guanylate Cyclase; D009638:Norepinephrine