Phospholipase C-independent effects of 3M3FBS in murine colon

• Published in: European journal of pharmacology 2010-02, Vol.628 (1), p.187-194
• Main Authors: Dwyer, Laura, Kim, Hyun Jin, Koh, Byoung Ho, Koh, Sang Don
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Calcium - metabolism; Colon - drug effects; Colon - enzymology; Colon - metabolism; Colon - physiology; Contractility; Delayed rectifier K + channel; Electric Conductivity; Isomerism; L-type Ca 2+ current; Medical sciences; Membrane potential; Mice; Mice, Inbred BALB C; Muscle Contraction - drug effects; Muscle, Smooth - drug effects; Muscle, Smooth - metabolism; Muscle, Smooth - physiology; Pharmacology. Drug treatments; Potassium - metabolism; Smooth muscle; Sulfonamides - chemistry; Sulfonamides - pharmacology; Type C Phospholipases - metabolism
• ISSN: 0014-2999; 1879-0712
• DOI: 10.1016/j.ejphar.2009.11.029

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.