Inhibition of intestinal motility by the putative BKCa channel opener LDD175

Abstract

LDD175 (4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid) is a benzofuroindole compound characterized previously as a potent opener of the large conductance calcium activated (BK(Ca)) channels. Activators of the BK(Ca) channels are potential therapies for smooth muscle hyperactivity disorders. The present study investigates the influence of LDD175 on the mechanical activity of the ileum smooth muscle. LDD175 inhibited spontaneous contractions of the ileum in a concentration-dependent manner (pEC(50)=5.9 +/- 0.1) (E (max)=96 +/- 1.0% at 100 muM, n=3). It also remarkably inhibited contractions due to acetylcholine (ACh) (pEC(50)=5.3 +/- 0.1)(E (max)=97.7 +/- 2.3%, n=6) and electrical field stimulation (EFS) (pEC(50)=5.5 +/- 0.1) (E (max)=83.3 +/- 6.0%, n=6). In strips precontracted by 20 mM KCl, LDD175 significantly reduced the contractions yielding a pEC(50) of 6.1 +/- 0.1 and E (max) of 96.6 +/- 0.9%, (n=6). In 60 mM KCl, a concentration-dependent inhibition was observed with respective pEC(50) and E (max) values of 4.1 +/- 0.1 and 50.8 +/- 5.0% (n=3). BK(Ca) channel blockers iberiotoxin (IbTX) and tetraethylammonium chloride (TEA, 1 mM) attenuated the relaxative effect of LDD175 but not barium chloride (BaCl(2)), and glibenclamide (K(IR) and K(ATP) channel blockers, respectively). These data demonstrate the antispasmodic activity of LDD175 attributable to the potentiation of the BK(Ca) channels.

4-Chloro-7-Trifluoromethyl-10<i>H-</i> Benzo[4,5]furo[3,2-<i>b</i>]Indole-1-Carboxylic Acid (TBIC), a Putative BK_Ca Channel Opener with Uterine Relaxant Activities

“…Nevertheless, we can observe the uterine relaxant activity of TBIC in agonist-induced contractions via interruption of Ca 2+ influx. Previously, dela Peña et al [21] have identified that TBIC (or LDD175 in their studies) inhibited spontaneous intestinal but not myogenic contractions of the bladder [22] . A number of factors, including species difference, may have brought such inconsistency.…”

“…Incubation period was based on previous experiments showing such time was sufficient for TBIC to exert relaxant activity [20,21] . Time control experiments were also performed, as well as control experiments where vehicle was added instead of TBIC.…”

“…Therefore, in our experiments, we added TBIC or atropine to the tissue in a single concentration manner. The methods were those as described previously [20,21] . Briefly, uterine strips were first subjected to precontraction by ACh (1 mol/l bath concentration) for 1 min and then washed out.…”

“…In some experiments, the tissues were exposed to 20 mmol/l KCl for 20 min and then to 100 nmol/l penitrem A [23] , 1 mmol/l TEA [24] , 10 mol/l BaCl 2 , and 10 mol/l glibenclamide [21] for 15 min before the addition of TBIC. These series of experiments were performed to identify which K + channel type TBIC specifically potentiates.…”

“…The chemical structure of TBIC is shown in figure 1 . In previous reports, dela Peña et al have demonstrated that TBIC (or LDD175) has bladder [20] and intestinal [21] relaxant activities. Moreover, despite the fact that BK Ca channels are abundantly expressed in muscles, putative BK Ca channel openers such as benzofuroindole compounds did not have significant influence on cardiovascular functions [20,22] .…”