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Small-conductance Ca(2+)-dependent K+ channels activated by ATP in murine colonic smooth muscle
S D Koh1, G M Dick, K M Sanders
1Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno 89557, USA.
Abstract:
The patch-clamp technique was used to determine the ionic conductances activated by ATP in murine colonic smooth muscle cells. Extracellular ATP, UTP, and 2-methylthioadenosine 5'-triphosphate (2-MeS-ATP) increased outward currents in cells with amphotericin B-perforated patches. ATP (0.5-1 mM) did not affect whole cell currents of cells dialyzed with solutions containing ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. Apamin (3 x 10(-7) M) reduced the outward current activated by ATP by 32 +/- 5%. Single channel recordings from cell-attached patches showed that ATP, UTP, and 2-MeS-ATP increased the open probability of small-conductance, Ca(2+)-dependent K+ channels with a slope conductance of 5.3 +/- 0.02 pS. Caffeine (500 microM) enhanced the open probability of the small-conductance K+ channels, and ATP had no effect after caffeine. Pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid tetrasodium (PPADS, 10(-4) M), a nonselective P2 receptor antagonist, prevented the increase in open probability caused by ATP and 2-MeS-ATP. PPADS had no effect on the response to caffeine. ATP-induced hyperpolarization in the murine colon may be mediated by P2y-induced release of Ca2+ from intracellular stores and activation of the 5.3-pS Ca(2+)-activated K+ channels.
Insights
Adenosine triphosphate (ATP) activates specific potassium channels in mouse colon smooth muscle cells, influencing cell electrical activity. This activation is mediated by P2Y receptors and calcium signaling pathways.
Area of Science:
- Physiology
- Pharmacology
- Cell Biology
Background:
- Adenosine triphosphate (ATP) plays a crucial role in cellular signaling.
- Purinergic signaling via P2 receptors is involved in smooth muscle function.
- Understanding ATP's effects on colonic smooth muscle is vital for gastrointestinal research.
Purpose of the Study:
- To investigate the ionic conductances activated by extracellular ATP in murine colonic smooth muscle cells.
- To identify the specific ion channels and signaling pathways involved in ATP-mediated responses.
- To elucidate the role of purinergic receptors in regulating colonic smooth muscle excitability.
Main Methods:
- Patch-clamp electrophysiology (whole-cell and single-channel recordings) was employed.
- Murine colonic smooth muscle cells were utilized for experiments.
- Pharmacological agents including apamin and PPADS were used to probe channel activity and receptor involvement.
Main Results:
- Extracellular ATP, UTP, and 2-MeS-ATP increased outward currents and the open probability of small-conductance, Ca(2+)-dependent K+ channels (5.3 pS).
- Apamin partially inhibited ATP-activated currents, and PPADS blocked ATP- and 2-MeS-ATP-induced channel activation, indicating P2 receptor mediation.
- Caffeine enhanced channel activity, and ATP had no further effect, suggesting a common downstream pathway.
Conclusions:
- ATP-induced hyperpolarization in murine colonic smooth muscle is likely mediated by P2Y receptor activation.
- This process involves the release of intracellular Ca(2+) and subsequent activation of 5.3-pS Ca(2+)-activated K+ channels.
- The findings provide insights into the purinergic regulation of colonic smooth muscle function.