Functional effects of β3-adrenoceptor on pacemaker activity in interstitial cells of Cajal from the mouse colon

We investigated the presence of β3-adrenoceptor and its functional effects on pacemaker potentials in colonic interstitial cells of Cajal (ICCs) from mice. The whole-cell patch clamp technique was used to record pacemaker potentials in cultured ICCs and reverse transcription polymerase chain reaction (RT-PCR) was performed to detect the mRNA transcript levels β-adrenoceptors. The β3-adrenoceptor agonist, BRL37344, reduced the frequency of pacemaker potentials in a concentration-dependent manner. The inhibitory effects of BRL37344 were blocked by the pretreatment of propranolol, a nonspecific β-adrenoceptor antagonist, but not by the selective β1-adrenoceptor antagonist atenolol and the selective β2-adrenoceptor antagonist butoxamine. β3-adrenoceptor antagonists SR59230A and L748337 blocked the inhibitory effects of BRL37344. RT-PCR revealed mRNA transcripts of β1- and β3-adrenoceptor, but not β2-adrenoceptor, in c-kit- and Ano-1-positive colonic ICCs. The K(+) channel blockers tetraethylammonium, apamin, and glibenclamide did not block the effects of BRL37344. N(ω)-Nitro-l-arginine methyl ester hydrochloride (L-NAME), an NO synthase inhibitor, and chelerythrine, a protein kinase C inhibitor, also did not block the effects of BRL37344. Noradrenaline mimicked the effects of BRL37344 in colonic ICCs. However, the inhibitory effects of noradrenaline on pacemaker potentials were blocked only by pretreatment with atenolol but not by butoxamine, SR59230A, or L748337. In small intestinal ICCs, BRL37344 had no effect on pacemaker potentials and mRNA transcripts of β1-and β2-adrenoceptor, but not β3-adrenoceptor were detected. These results suggest that β3-adrenoceptors are present in colonic ICCs and may play a role in regulating gastrointestinal motility by the inhibition of pacemaker potentials.