P2Y1 Receptors Mediate Apamin-Sensitive and -Insensitive Inhibitory Junction Potentials in Murine Colonic Circular Smooth Muscle

Purinergic inhibitory neuromuscular transmission plays an important role in the control of intestinal motility. In most tissues this neurotransmission is apamin-sensitive, but recent studies in human colonic circular smooth muscle (CSM) suggest the presence of apamin-insensitive purinergic inhibitory junction potentials (IJPs). The current studies used conventional intracellular recordings on colonic CSM strips to characterize the purinergic IJPs in murine colonic CSM. P2Y(1) receptor expression was examined by using reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. The IJP induced by nerve stimulation (NS) of one and four pulses in neuronal nitric-oxide synthase knockout mice consists of an apamin-sensitive and a dominant apamin-resistant component. These are identical to the IJPs in wild-type and CD1 mice in the presence of N-omega-nitro-L-arginine methyl ester (200 mu M) and were significantly inhibited by alpha,beta-methylene ATP (50 mu M), an analog of ATP. IJPs were not affected by the P2X receptor antagonist 2',3'-o-(2,4,6-trinitrophenyl)-ATP (10 mu M). Furthermore, apamin-resistant IJPs induced by single-pulse NS were abolished by pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (100 mu M), a P2 receptor antagonist; 2'-deoxy-N6-methyl adenosine 3,5-diphosphate (MRS-2179; 10 mu M), a selective P2Y(1) receptor antagonist; and tetrodotoxin (1 mu M). Aboral NS induced apamin-sensitive purinergic IJPs, whereas oral and circumferential NS produced apamin- sensitive and -resistant IJPs, with the latter predominating. RT-PCR and immunohistochemistry confirmed the presence of P2Y(1) receptors on smooth muscle and in the myenteric plexus. These data suggest that, depending on stimulus location, activation of P2Y(1) receptors produces both apamin- sensitive and apamin- resistant IJPs in murine colonic CSM.