| 19931239 |
Dwyer L, Kim HJ, Koh BH, Koh SD: Phospholipase C-independent effects of 3M3FBS in murine colon. . Eur J Pharmacol. 2010 Feb 25;628(1-3):187-94. Epub 2009 Nov 18.
The muscarinic receptor subtype M (3) is coupled to Gq/11 proteins. Muscarinic receptor agonists such as carbachol stimulate these receptors that result in activation of phospholipase C (PLC) which hydrolyzes phosphatidylinositol 4,5-bisphosphate into diacylglycerol and Ins (1,4,5) P (3). This pathway leads to excitation and smooth muscle contraction. In this study the PLC agonist, 2, 4, 6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)-benezenesulfonamide (m-3M3FBS), was used to investigate whether direct PLC activation mimics carbachol-induced excitation. We examined the effects of m-3M3FBS and 2, 4, 6-trimethyl-N-(ortho-3-trifluoromethyl-phenyl)-benzenesulfonamide (o-3M3FBS), on murine colonic smooth muscle tissue and cells by performing conventional microelectrode recordings, isometric force measurements and patch clamp experiments. Application of m-3M3FBS decreased spontaneous contractility in murine colonic smooth muscle without affecting the resting membrane potential. Patch clamp studies revealed that delayed rectifier K (+) channels were reversibly inhibited by m-3M3FBS and o-3M3FBS. The PLC inhibitor, 1-(6-((17b-3-methoxyestra-1,3,5 (10)-trien-17-yl) amino) hexyl)-1H-pyrrole-2, 5-dione (U73122), did not prevent this inhibition by m-3M3FBS. Both m-3M3FBS and o-3M3FBS decreased two components of delayed rectifier K (+) currents in the presence of tetraethylammonium chloride or 4-aminopyridine. Ca (2+) currents were significantly suppressed by m-3M3FBS and o-3M3FBS with a simultaneous increase in intracellular Ca (2+). Pretreatment with U73122 did not prevent the decrease in Ca (2+) currents upon m-3M3FBS application. In conclusion, both m-3M3FBS and o-3M3FBS inhibit inward and outward currents via mechanisms independent of PLC acting in an antagonistic manner. In contrast, both compounds also caused an increase in [Ca (2+)](i) in an agonistic manner. Therefore caution must be employed when interpreting their effects at the tissue and cellular level. |
2(0,0,0,2) |