Acta Physiologica 2010; Volume 199, Supplement 678
Belgian Society for Fundamental and Clinical Physiology and Pharmacology, Spring Meeting 2010
FacultÚs Universitaires de la Paix, Namur, Belgium
HEMICHANNEL INVOLVEMENT IN CA2+ DYNAMICS AND CONTRACTILITY OF SMOOTH MUSCLE CELLS IN ACUTELY ISOLATED SMALL MESENTERIC ARTERIES
Abstract number: P-06
Bol1 M., De Bock1 M., De Vuyst1 E., Wang1 N., Decrock1 E., Monsalvo1 J., Decaluwe2 K., Vanheel1 B., Van de Voorde2 J., Leybaert1 L.
Intracellular Ca2+ mediates a variety of vascular endothelial and smooth muscle cell functions. Smooth muscle cells (SMC) respond to biological activators with oscillatory and propagating rises in [Ca2+]i that are highly organized in both time and space. Gap junctions (GJs) play a crucial role in the communication between vascular cells and in the synchronization of Ca2+ signals thereby tightly controlling the level of vasoconstriction. Before being incorporated into GJs, connexin (Cx) hemichannels reside in the plasma membrane in a closed state. Recent evidence suggests that hemichannels can be opened by various messengers and conditions, thereby forming a pore that allows the passage of ATP and ions. Using confocal microscopy and the Ca2+ sensitive dye Fluo-3, we examined the role of hemichannels in dynamic Ca2+ responses of SMC in intact acutely isolated small rat mesenteric arteries. Furthermore, we assessed the involvement of these signalling partners in contractile responses of small mesenteric arteries using a wire myograph for isometric tension measurements. Importantly, the experimental conditions were such that vasomotion, characterized by synchronized Ca2+ signals, was avoided because in that case gap junctions between SMC and myo-endothelial gap junctions are expected to contribute. Norepinephrine (NOR, 3 mM) induced Ca2+ oscillations that were reduced in frequency by 98.4 % (p< 0.05) when exposed to carbenoxolone (CBX, 50 mM), a none specific Cx channel inhibitor. Gap27 (200 mM), a Cx mimetic peptide that blocks hemichannel responses (assayed by ATP release and dye uptake) after short incubation, reduced the spiking frequency by 96.4 % (p< 0.05). Suramin (200 mM) and PPADS (75 mM), two P2Y receptor antagonists, decreased the spiking frequency by 90.5 % (p<0.05) and 96.4% (p<0.01) respectively. Apyrase (5 U/ml), an enzyme that rapidly degrades extracellular ATP, reduced the spiking frequency by 71.4 % (p<0.01). None of these agents affected the amplitude of the Ca2+ oscillations. Both gap27 (56.6 %, p<0.01) and CBX (53.4 %, p<0.05) reduced the NOR-induced contractions. Incubation with suramin decreased the NOR-induced contractions by 31.6 % (p<0.001). Our results suggest a role for Cx hemichannels and purinergic signaling in Ca2+ oscillations and contractility.
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Acta Physiologica 2010; Volume 199, Supplement 678 :P-06