Endothelium‐dependent Vasodilation in Myogenically Active Mouse Skeletal Muscle Arterioles: Role of EDH and K⁺ Channels

Abstract

As smooth muscle cell (SMC) membrane potential (E(m)) is critical for vascular responsiveness, and arteriolar SMCs are depolarized at physiological intraluminal pressures, we hypothesized that myogenic tone impacts on dilation mediated by endothelium-derived hyperpolarization (EDH). Studies were performed on cannulated mouse cremaster arterioles [diameter, 33+/-2 microm (n=23) at 60 mmHg; SMC Em -34.6+/-1.2 mV (n=7)]. Myogenic activity was assessed as tone developed in response to intraluminal pressure. Functional observations were related to mRNA, protein expression, and anatomy. Acetylcholine concentration-response curves showed a modest shift following indomethacin (10 microM) and L-NAME (100 microM), although maximal vasodilation was achieved. Residual dilation was removed by apamin (1 microM) in combination with TRAM-34 (1 microM) or charybotoxin (0.1 microM), indicating the requirement of small (S) and intermediate (I) calcium-activated potassium channels (K(Ca)). Charybdotoxin, but not TRAM-34, caused vasoconstriction, presumably through the inhibition of SMC BK(Ca). Expression of SK3 and IK1 was confirmed by immunohistochemistry and polymerase chain reaction, while myoendothelial junctions were common, suggesting a high degree of cell coupling. Also consistent with a role for endothelial K(Ca) channels, acetylcholine increased endothelium [Ca(2 +)](i). Apamin and TRAM-34 similarly blocked EDH-mediated dilation at intraluminal pressures of 30 and 90 mmHg, suggesting that in mouse arterioles, SK(Ca -) and IK(Ca -) mediated mechanisms predominate and operate independently of physiological levels of myogenic activation.

Chronic Hypoxia Inhibits Pregnancy-Induced Upregulation of SK Ca Channel Expression and Function in Uterine Arteries

“…This is in agreement with the previous findings in myocytes of rabbit aorta 29 and rat myometrium 36 that apamin reduced whole-cell K + currents by about 20%. Furthermore, previous studies also have shown the presence of SK Ca channels in other visceral and vascular smooth muscle cells by immunohistochemistry, 31, 49, 50 although the functional roles of these channels are not known. In uterine arteries, NS309-induced relaxation was largely endothelium-independent, suggesting that SK Ca channels in vascular smooth muscle mediated mainly NS309-induced vasorelaxation.…”

What's Where and Why at a Vascular Myoendothelial Microdomain Signalling Complex

“…in vitro, respectively), despite the demonstration of MEGJs in these vessels. 35,87 This apparently contradictory observation is likely related to the use of anaesthetic in the in vivo studies. Indeed, the potential for anaesthetics to produce effects that inhibit specific aspects of dilator and constrictor function has considerable implications for the interpretation of data in many previous studies.…”

“…Studies of intact vessels in chronically anaesthetized animals in vivo and of the same isolated pressurized vessels in vitro yield apparently contradictory results, namely the absence of myoendothelial coupling in vivo and the presence of such coupling in vitro (hamster cheek pouch 84,85 and mouse cremaster 86,87 arteriole in vivo cf. in vitro, respectively), despite the demonstration of MEGJs in these vessels.…”

“…Studies of vessel function in vivo require experimental animals to be chronically anaesthetized and the apparent lack of MEGJ coupling in this state is consistent with anaesthetics having effects on endothelium-dependent vasodilator activity (cf. data for hamster cheek pouch 84,85 and data for mouse cremaster 86,87 ). Indeed, the in vivo use of isoflurane, halothane, ketamine, pentobarbitol and etomidate results in antagonism of NO and EDH.…”

Activation of KCa3.1 by SKA‐31 induces arteriolar dilatation and lowers blood pressure in normo‐ and hypertensive connexin40‐deficient mice

“…In the murine vasculature, both channels are selectively expressed in endothelial cells (Brähler et al, 2009;Potocnik et al, 2009). Up to now, in vitro studies have shown that SKA-31 enhances ACh-induced dilatation of murine carotid arteries and of canine mesenteric arteries in the presence of a vasospasm agent (Sankaranarayanan et al, 2009;Damkjaer et al, 2012).…”