Submitted on January 29, 2008
Accepted on April 14, 2008
ATP Induces Guinea Pig Gallbladder Smooth Muscle Excitability via the P2Y4 Receptor and COX-1 Activity
Aaron C Bartoo1, Mark T Nelson2, and Gary M. Mawe3*
1 Anatomy and Neurobiology, University of Vermont, Burlington, Vermont, United States
2 Pharmacology, University of Vermont, Burlington, United States
3 Department of Anatomy and Neurobiology, University of Vermont, Burlington, United States; Anatomy and Neurobiology, University of Vermont, Burlington, Vermont, United States; Pharmacology, University of Vermont, Burlington, United States
* To whom correspondence should be addressed. E-mail: gary.mawe{at}uvm.edu.
The purpose of this study was to elucidate the mechanisms by which ATP increases guinea pig gallbladder smooth muscle (GBSM) excitability. We evaluated changes in membrane potential and action potential frequency in GBSM using intracellular recording. Application of ATP (100 µM) caused membrane depolarization and a significant increase in AP frequency that were not sensitive to block by tetrodotoxin (0.5 µM). The non-selective P2 antagonist, suramin (100 µM), blocked the excitatory response, resulting in decreased AP frequency in the presence of ATP. The excitatory response to ATP was not altered by PPADS (30 µM), a non-selective P2X antagonist. UTP also caused membrane depolarization and increased AP frequency, with a similar dose-response relationship as ATP. RT-PCR demonstrated that the P2Y4, but not P2Y2, receptor subtype is expressed in guinea pig gallbladder muscularis. ATP induced excitation was blocked by indomethacin (10 µM) and the COX-1 inhibitor, SC-560 (300 nM), but not the COX-2 inhibitor, nimesulide (500 nM). These data suggest that ATP stimulates P2Y4 receptors within the gallbladder muscularis and, in turn, stimulate prostanoid production via COX-1 leading to increased excitability of GBSM.
Introduction
