Smooth muscle α_1D‐adrenoceptors mediate phenylephrine‐induced vasoconstriction and increases in endothelial cell Ca²⁺ in hamster cremaster arterioles

Abstract

Background and purpose: a 1 -Adrenoceptor agonists induce Ca 2 þ -transients in endothelial cells (ECs) of arterioles. However, the presence of a 1 -adrenoceptors on arteriolar ECs has not been excluded, and the identity of a 1 -adrenoceptor subtypes in arterioles only has been inferred from pharmacology. Therefore, we determined which subtypes were expressed by vascular smooth muscle cells (VSMCs) and ECs, and which subtype mediated a 1 -adrenoceptor-induced constriction. Experimental approach: EC Ca 2 þ -transients in isolated, cannulated hamster cremasteric arterioles or freshly isolated ECs were studied using Fura 2. Arteriolar diameter was measured by video microscopy. a 1 -Adrenoceptor expression was assessed by western blot of whole-arteriolar homogenates and real-time RT-PCR on enzymatically isolated VSMCs and ECs. Key results: Phenylephrine-induced constriction and EC Ca 2 þ -transients were abolished by the a 1 -adrenoceptor antagonist prazosin (30 nM) in arterioles. Phenylephrine-induced constriction was inhibited by the a 1D -adrenoceptor antagonist BMY 7378 (K B ¼ 2.96 nM) and the a 1A -adrenoceptor antagonist 5-methylurapidil (K B ¼ 4.08 nM), suggesting a significant role for a 1D -adrenoceptors. Western blots confirmed a 1D -adrenoceptor expression, but did not detect a 1A -adrenoceptors. VSMCs expressed a 1D -and a 1A -, but not a 1B -, adrenoceptor transcripts. No a 1 -adrenoceptor transcripts were detected in ECs. Neither phenylephrine (10 mM) nor noradrenaline (0.1-1 mM) elicited Ca 2 þ -transients in freshly isolated ECs, whereas the endotheliumdependent vasodilators methacholine (1 mM) and substance P (100 nM) consistently increased Ca 2 þ . Conclusions and implications:We reject the hypothesis that hamster cremasteric arteriolar ECs express a 1 -adrenoceptors and conclude that a 1 -adrenoceptor agonists predominantly act on VSMC a 1D -adrenoceptors to cause vasoconstriction and a subsequent rise in EC Ca 2 þ .

Heterogeneous function of ryanodine receptors, but not IP3receptors, in hamster cremaster muscle feed arteries and arterioles

“…Arterioles and feed arteries with intact endothelium were transferred to a cannulation chamber using a 50 -100-l Wiretrol pipette (Drummond Scientific, Broomal, PA), cannulated onto glass micropipettes, and secured to the pipettes using 11-0 ophthalmic suture (Ashaway Line and Twine, Ashaway, RI). The chamber was then secured to the stage of a microscope (Leica DMIL, Wetzlar, Germany) where the vessels were visualized, heated to 34°C (cremaster arterioles) or 37°C (feed arteries), pressurized to 80 cmH2O and allowed to develop myogenic tone (14,40). All vessels studied had a minimum of 20% resting myogenic tone compared with the maximum diameters of the vessels obtained in Ca 2ϩ -free PSS.…”

Aging increases capacitance and spontaneous transient outward current amplitude of smooth muscle cells from murine superior epigastric arteries

“…The vessels were tested for leaks by pressurization to 80 cmH2O with no flow through the lumen while immersed in Dissection Solution to obtain maximal diameter and adjust their length to approximate that in situ. If the vessels were leak-free, then transmural pressure was reduced to 20 cmH 2O and they were superfused with Ca 2ϩ -containing PSS, warmed to 37°C and internal diameter measured (9,22,49,50). Only leak-free vessels were studied; no other selection criteria were applied.…”

Pannexin-1 channels and their emerging functions in cardiovascular diseases

“…Therefore, the Pannexin-1/ATP signaling pathway is speculated to participate in the regulation of vascular tone and blood pressure [25,45,[85][86][87][88]. Smooth muscle cells, which contribute to peripheral resistance, are highly innervated by the sympathetic nervous system [89]. Endogenous catecholamines, such as epinephrine and norepinephrine, are released from the sympathetic nerve fibers and contract the vessel smooth muscle via the α1-adrenergic receptor [90].…”