Effect of quercetin on colon contractility and L-type Ca(2+) channels in colon smooth muscle of guinea-pig / 生理学报

The aim of the present study was to investigate the effects of quercetin on colon contractility and voltage-dependent Ca(2+) channels in the single smooth muscle cell isolated from the proximal colon of guinea-pig and to clarify whether its effect on L-type Ca(2+) current (I(Ca,L)) would be related to its myorelaxing properties. Colon smooth muscle strips were used to take contractile tension recordings. Smooth muscle cells were freshly isolated from the proximal colon of guinea-pig by means of papain treatment. I(Ba,L) (barium instead of calcium as current carrier) was measured by using whole-cell patch-clamp techniques. The results showed that quercetin relaxed colon muscle strips in a concentration-dependent manner and antagonized the contractile effect of acetylcholine and neostigmine. Preincubation with indomethcin [cyclooxygenase (COX) inhibitor] and methylene blue [guanylate cyclase (GC) inhibitor] significantly attenuated the relaxing effect of quercetin, respectively. Quercetin increased I(Ba,L) in a concentration- [EC(50)= (7.59+/-0.38) mumol/L] and voltage-dependent pattern, and shifted the maximum of the current-voltage curve by 10 mV in the depolarizing direction without modifying the threshold potential for Ca(2+) influx. Quercetin shifted the steady-state inactivation curve toward more positive potentials by approximately 3.75 mV without affecting the slope of activation and inactivation curve. H-89 (PKA inhibitor) abolished quercetin-induced I(Ba,L) increase, while cAMP enhanced the quercetin-induced I(Ba,L) increase. The patch-clamp results proved that quercetin increased I(Ba,L) via PKA pathway. It is therefore suggested that the relaxing effect of quercetin attributes to the interaction of GC and COX stimulation, as well as the antagonism effect on acetylcholine, which hierarchically prevails over the increase in the Ca(2+) influx to be expected from I(Ca,L) stimulation.

The characteristics and oxidative modulation of large-conductance calcium-activated potassium channels in guinea-pig colon smooth muscle cells / 生理学报

To investigate the characteristics of large-conductance calcium-activated potassium channels (BK(Ca)) and the effect of hydrogen peroxide (H2O2) on BK(Ca) in guinea-pig proximal colon smooth muscle cells, single smooth muscle cells of guinea-pig colon were enzymatically isolated in low calcium solution containing papain (3 mg/mL), DTT (2 mg/mL), and bovine serum albumin (BSA, 2 mg/mL). Tissues were incubated at 36 degrees C in enzyme solution for 15 min and were then suspended in enzyme-free low calcium solution. Inside-out single channel recording technique was used to record BK(Ca) current. The intracellular (bath) and microelectrode solution both contained symmetrical high potassium. The BK(Ca) in guinea-pig colon smooth muscle cell possesses: 1) voltage-dependence, 2) high selectivity for potassium ion, 3) large conductance (223.7 pS+/-9.2 pS), 4) dependence of [Ca(2+)](i). Intracellular application of H2O2 decreased the open probability (P(o)) of BK(Ca) at low concentration (</=1 mmol/L), and increased or decreased P(o) of BK(Ca) at high concentration (5 mmol/L), without affecting the unitary conductance. The effects of H2O2 were reversed by reducing agent dithiothreitol (DTT). Similarly, cysteine specific oxidizing agent, DTNB, also increased or decreased P(o) of BK(Ca) and DTT partially reversed the effect of DTNB. It is thus suggested that H2O2 and DTNB may modulate P(o) of BK(Ca) via the oxidation of cysteine residue.

Effect of genistein on L-type calcium channel currents of proximal colon smooth muscle cells of guinea-pig / 中国药理学与毒理学杂志

AIM To study the effect of genistein (GST), a protein tyrosine kinases inhibitor, on L-type calcium channel currents (Iba,L or Ica,L, dependent on permeating ion used) in freshly dispersed colon smooth muscle cells from guinea-pig. METHODS Single colon smooth muscle cells were enzymatically dissociated from guinea-pig. L-type calcium currents were measured by conventional whole-cell patch-clamp techniques. RESULTS The peak amplitudes of Iba,L elicited to 10 mV test potential from a holding potential of -80 mV, were reversibly and dose-dependently reduced by GST (10-100 μmol·L-1) with an IC50 value of (39.9±3.6)μmol·L-1. Bath application of GST shifted the steady-state inactivation curves of Iba,L in a hyperpolarized direction (about 10 mV, P＜0.01) without altering their slopes. The peak amplitudes of Iba,L were also inhibited but to a less extent by daidzein, an inactive analogue of GST. Sodium orthovanadate 1 mmol·L-1, a potent inhibitor of protein tyrosine phosphatases, blocked GST-induced inhibition of Ica,L. CONCLUSION GST can block L-type calcium channel activity in guinea-pig colon smooth muscle cells via tyrosine kinase pathway.

Emodin blocks voltage dependent potassium channels in rat proximal colon smooth muscle cells / 药学学报

<p><b>AIM</b>To investigate the effect of emodin on the voltage dependent potassium (K(V)) currents in rat proximal colon smooth muscle cells.</p><p><b>METHODS</b>Whole cell patch clamp technique was used to record potassium currents including fast transient outward current (I(KA)) and delayed rectifier current (I(Kdr)). Contamination of calcium-dependent potassium currents was minimized with CdCl2 in external solution and EGTA in pipette solution.</p><p><b>RESULTS</b>Emodin (1-30 micromol x L(-1)) reversibly and dose-dependently reduced the amplitude of I(Kdr) with an K(d) value of (1.9 +/- 0.1) micromol x L(-1). I(KA) was also inhibited with 30 micromol x L(-1) emodin to a lesser extent. Although acceleration of the decay rate of the K(V) currents was observed, the block by emodin was not through open block mechanism because a steady state level of inhibition of I(Kdr) was achieved during the first pulse from holding potential -70 mV to + 50 mV after the cells were holding at -70 mV for a three minutes interval in the presence of emodin. Emodin (5 micromol x L(-1)) had no effect on the steady-state activation and inactivation kinetics of K(V) currents, but 30 micromol x L(-1) of emodin produced a positive shift of the voltage dependence of activation, and an increase in the steepness of activation gating as well as shifted the voltage dependence of inactivation to positive direction.</p><p><b>CONCLUSION</b>Emodin, not through open block mechanism, markedly reduced the amplitude of I(KA) and I(Kdr) and modulated the gating properties of K(V) channels in a reversible and dose-dependent manner.</p>