Extracellular Mg2+ blocks endothelin-1-induced contraction through the inhibition of non-selective cation channels in coronary smooth muscle

Abstract

This study investigated the effects of changing the extracellular [Mg(2+)] ([Mg(2+)](o)) on endothelin-1 (ET-1)-induced contraction of rabbit coronary artery smooth muscle and the involvement of non-selective cation (NSC) channels in this response. Increased [Mg(2+)](o) shifted the concentration/contraction relationship curve of ET-1 to the right. In whole-cell patch clamp recordings, ET-1 (10(-7) M) induced a long-lasting inwards current (94.7+/-7.2 pA) that was inhibited by 8 mM [Mg(2+)](o) (45.3+/-4.4%) and NSC channel blockers (10(-3) M streptomycin and 10(-3) M La(3+)), but not by the voltage-dependent Ca(2+) channel blocker nicardipine. The current/voltage (I/V) curve was linear. Furthermore, in pressurized arteries, the ET-1-induced contraction was also inhibited by La(3+) and streptomycin, but not by nicardipine. U-73122, a selective phospholipase C (PLC) inhibitor and staurosporine and GF 109203X, which block protein kinase C (PKC), reduced ET-1-activated NSC currents by 54.2+/-5.1%, 60.3+/-5.5% and 48.5+/-2.9%, respectively. The inwards current was increased by 1-oleoyl-2-acetyl-sn-glycerol (OAG) and phorbol 12,13-dibutyrate (PDBu), which activate PKC selectively. Like transient receptor potential channel (TRPC3) currents, ET-1-activated NSC currents had a linear I/V relationship, were blocked by flufenamate and activated by a diacylglycerol analogue. These results suggest that [Mg(2+)](o) blocks ET-1-induced contraction of coronary arteries by inhibiting NSC channels. Activation of PLC and PKC might be involved in activation of NSC channels.

Mechanosensitive nonselective cation channel facilitation by endothelin-1 is regulated by protein kinase C in arterial myocytes

“…Therefore, we believe that the present study demonstrates genuine facilitation of NSC MS by ET-1. Nonetheless, considering previous report on ET-1 activated cationic currents in whole-cell recordings [37][38][39], the absence of channel activation by ET-1 alone in the present study is difficult to explain. The Ca 2+ -free condition might be supposed as a factor suppressing the activation of other cation channels by ET-1.…”

“…Previous studies have shown that ET-1 modulates various kinds of ion channels, e.g. it inhibits K ATP and K v channels [32][33][34], and stimulates L-type Ca 2+ channels, Cl − channels, and nonselective cation channels [23,[35][36][37][38][39]. These changes commonly imply that ET-1 has a depolarizing effect on vascular smooth muscle cells.…”

“…Because stimulation with ET-1 is known to activate nonselective cation channels in vascular myocytes via signaling cascades like phospholipase C [37][38][39], we were initially concerned as to whether increased channel activity reflects NSC MS facilitation or an additive activation of receptor-operated cation channels. However, the present study demonstrates that the application of ET-1 alone does not activate single-channel currents (Fig.…”

Effects of Magnesium Treatment in a Model of Internal Capsule Lesion in Spontaneously Hypertensive Rats

“…27 Several mechanisms for the vascular effects of magnesium have been proposed, including antioxidant actions, blockade of voltage-dependent calcium channels, release of NO, 28 and inhibition of ET-1 vasoconstriction. 29 However, if the severity or duration of ischemia were reduced by magnesium, one would expect a reduction in infarct volume, and this was not apparent in our data.…”

Calcium Channel Inhibitor, Verapamil, Inhibits the Voltage-Dependent K+ Channels in Rabbit Coronary Smooth Muscle Cells

“…Single vascular smooth muscle cells were mechanically dispersed by triturating the arteries after two step enzyme treatment with papain (1 mg/ml) and collagenese (1.5 mg/ml) in Ca 2ϩ -free normal Tyrode solution as described previously. 18) Cells were kept at 4°C under Kraft-Brühe (KB) and used within the same day. KB solution contained (in mM): 70 KOH, 50 L-glutamate, 20 KH 2 PO 4 , 55 KCl, 20 taurine, 3 MgCl 2 , 20 glucose, 10 N-(2-hydroxyethyl)piperazine-N Ј-2-ethanesulfonic acid (HEPES), 0.5 EGTA adjusted to pH 7.3 with KOH.…”