Size‐dependent heterogeneity of contractile Ca²⁺ sensitization in rat arterial smooth muscle

Abstract

Key points• Each segment along arterial vessels adapts to different circumstances, such as high blood pressure in the central and low pressure in the peripheral arteries and high sympathetic innervation in the peripheral and low innervation in the central arteries.• We tested, using pharmacological tools, whether the amplitude and time course of each signalling pathway varies dynamically between arterial segments in rat.• In small mesenteric arteries, α 1 -agonist produced a contraction and myosin light chain phosphorylation through sequential activation of α 1A -subtype receptors, Ca 2+ , PKC and protein kinase C-potentiated protein phosphatase inhibitor protein 17 kDa (CPI-17).• In large aorta, α 1 -agonist-induced contraction and phosphorylation were produced through activation of α 1D receptors followed by a Ca 2+ increase and constitutively active Rho-kinase in an independent manner. The results for midsized arteries were intermediate.• Our findings provide insights into the development of new therapeutic agents controlling the size-dependent vasoconstriction.Abstract Each segment along arterial vessels adapts to different circumstances, including blood pressure and sympathetic innervation. PKC and Rho-associated kinase (ROCK) Ca 2+ -sensitizing pathways leading to myosin phosphatase inhibition are critically involved in α 1 -adrenoceptor-mediated vascular smooth muscle contraction in distinctive time-dependent manners. We tested whether the amplitude and time course of each pathway varies dynamically between arterial segments. Using pharmacological approaches, we determined the time-dependent roles of Ca 2+ release, Ca 2+ influx, PKC and ROCK in α 1 -agonist-induced contraction and phosphorylation of key proteins in denuded rat small mesenteric artery, midsized caudal artery and thoracic aorta. SR Ca 2+ release and voltage-dependent Ca 2+ influx were essential for the initial rising and late sustained phases, respectively, of phenylephrine-induced contraction, regardless of arterial size. In small mesenteric arteries, α 1A -subtype-specific antagonists and inhibitors of PKC, but not ROCK, markedly reduced the initial and late phases of contraction in a non-additive manner and suppressed phosphorylation of myosin light chain (MLC) and CPI-17, but not myosin targeting subunit of myosin light chain phosphatase (MYPT1). In aorta, an α 1D -specific antagonist reduced both the initial and late phases of contraction with a significant decrease in MLC but not CPI-17 or MYPT1 phosphorylation. ROCK inhibitors, but not PKC inhibitors, suppressed the sustained phase of contraction with a decrease in MLC and MYPT1 phosphorylation in the aorta. The effect of ROCK inhibitors was additive with the α 1D -antagonist. The results for midsized arteries were intermediate. Thus, the PKC-CPI-17 Ca 2+ -sensitizing pathway, which is dependent on PKC subtype and a Ca 2+ -handling mechanism, and is downstream of α 1A receptors, plays a major role in α 1 -agonist-induced contraction of small resistance arteries in the splanchnic vasc...

Signaling through Myosin Light Chain Kinase in Smooth Muscles

“…Thus, aortic tissue appears to be highly dependent on MLCK content without robust Ca 2ϩ sensitization responses. This conclusion is consistent with the recent analysis of heterogeneity of Ca 2ϩ sensitization responses in arteries of different sizes, including the aorta (57).…”

“…This represents a 3-fold increase over basal phosphorylation. However, the more quantitative measurement shows how small the CPI-17 phosphorylation response is, consistent with its minimal contribution to Ca 2ϩ sensitization in aortic tissues (57). Similarly, basal MYPT1 phosphorylation was high and increased modestly with phenylephrine treatment, consistent with recent observations (57).…”

Neural programming of mesenteric and renal arteries

“…11). The inhibitory subunit of MP, CPI-17, is more highly expressed in tonic vs. phasic smooth muscle (52) and is proposed to play more of a role in ␣-adrenergic-mediated inhibition of MP in SRAs vs. large arteries (27) (reviewed in Ref. 13).…”

A role for the Ca2+-dependent tyrosine kinase Pyk2 in tonic depolarization-induced vascular smooth muscle contraction

“…In addition, most contractile stimuli acting via GPCRs induce an increase in MYPT1 phosphorylation at Thr855 but not at Thr697 (e.g. Borysova et al 2011;Kitazawa and Kitazawa 2012). The complete pathway of Ca 2?…”