Cell-volume-dependent vascular smooth muscle contraction: role of Na+, K+, 2Cl? cotransport, intracellular Cl? and L-type Ca2+ channels

Abstract

This study elucidates the role of cell volume in contractions of endothelium-denuded vascular smooth muscle rings (VSMR) from the rat aorta. We observed that hyposmotic swelling as well as hyper- and isosmotic shrinkage led to VSMR contractions. Swelling-induced contractions were accompanied by activation of Ca2+ influx and were abolished by nifedipine and verapamil. In contrast, contractions of shrunken cells were insensitive to the presence of L-type channel inhibitors and occurred in the absence of Ca2+ o. Thirty minutes preincubation with bumetanide, a potent Na+, K+, CI- cotransport (NKCC) inhibitor, decreased Cl(-)i content, nifedipine-sensitive 45Ca uptake and contractions triggered by modest depolarization ([K+]o = 36 mM). Elevation of [K+]o to 66 mM completely abolished the effect of bumetanide on these parameters. Bumetanide almost completely abrogated phenylephrine-induced contraction, partially suppressed contractions triggered by hyperosmotic shrinkage, but potentiated contractions of isosmotically shrunken VSMR. Our results suggest that bumetanide suppresses contraction of modestly depolarized cells via NKCC inhibition and Cl(-)i-mediated membrane hyperpolarization, whereas augmented contraction of isosmotically shrunken VSMR by bumetanide is a consequence of suppression of NKCC-mediated regulatory volume increase. The mechanism of bumetanide inhibition of contraction of phenylephrine-treated and hyperosmotically shrunken VSMR should be examined further.

Effects of High-K+, Na+-Deficient Solution on Contractility of the Smooth Muscles of the Bovine Trachea

“…The relaxing mechanism of swelling may be explained in the following two ways: 1) effects on intracellular Ca 2+ movement and 2) an inhibition of contractile elements. It has been suggested that Cl -movement is related to the [Ca 2+ ]i level in canine basilar arteries [26] and the rat aorta [1] and trachea [4]. However, in our study, I-154 K + solution induced a sustained increase of [Ca 2+ ]i level in the bovine trachea.…”

Myogenic tone in mouse mesenteric arteries: evidence for P2Y receptor-mediated, Na+, K+, 2Cl− cotransport-dependent signaling

“…Effect of bumetanide with data obtained in a study on contractions of depolarized endothelium-denuded strips from rat aortae [22]. We did not observe any inhibitory action of bumetanide on contractions triggered by ATP, whereas contractions of UTP-treated arteries were decreased by 60% (Fig.…”

“…Ca 2+ release from the endoplasmic reticulum elicits activation of Cl − channels, plasma membrane depolarization and activation of long-lasting L-type Ca 2+ channels, whose involvement in MT is well-documented in an overwhelming number of vessels studied so far [3]. Significantly, NKCC inhibition partially blocked the depolarizing action of Cl − channel activation via attenuation of [Cl -] i , as demonstrated in bumetanide-and furosemidetreated smooth muscle cells of different origins [20][21][22], and resulted in the MT suppression documented here (Fig. 6).…”

“…The distinct action of bumetanide on ATP-and UTP-induced contractions is consistent with different mechanisms of action of these nucleotides on excitation-constriction coupling. Indeed, in rat mesenteric arteries, UTP triggered modest and sustained depolarization from −60 to −50 mV [44] that was probably caused by the activation of Ca 2+ -sensitive Cl − channels and could be abolished by the addition of bumetanide that decreases [Cl − ] i and approaches Nernst Cl − equilibrium potential to resting E m [20][21][22]. Unlike UTP, ATP affected VSMC contractions via transient activation of Ca 2+ influx through P2X ion channels and independently of E m modulation [44].…”

“…These data suggest that highceiling diuretics suppress MT of the renal afferent arterioles via NKCC inhibition, attenuation of [Cl − ] i and VSMC hyperpolarization. Indeed, both furosemide and bumetanide decrease [Cl − ] i [20][21][22], hyperpolarize VSMC [21], suppress the activation of L-type Ca 2+ channels [22] and reduce the baseline tone of vascular and non-vascular smooth muscles [23][24][25] as well as contractions triggered by diverse stimuli, including [K + ] o -induced depolarization [22], phenylephrine [22,[26][27][28], histamine [29], angiotensin II [30], thromboxane A 2 [31,32], and oxytocin [33,34]. Recently, it was demonstrated that high-ceiling diuretics, such as bumetanide and furosemide that are known to be potent NKCC inhibitors, almost completely abolished the MT of renal afferent arterioles in perfused hydronephrotic rat kidneys in vitro [32].…”