title: Nanomolar ouabain increases NCX1 expression and enhances Ca2+ signaling in human arterial myocytes: a mechanism that links salt to increased vascular resistance?
abstract: The mechanisms by which NaCl raises blood pressure (BP) in hypertension are unresolved, but much evidence indicates that endogenous ouabain is involved. In rodents, arterial smooth muscle cell (ASMC) Na(+) pumps with an α(2)-catalytic subunit (ouabain EC(50) ≤1.0 nM) are crucial for some hypertension models, even though ≈80% of ASMC Na(+) pumps have an α(1)-subunit (ouabain EC(50) ≈ 5 μM). Human α(1)-Na(+) pumps, however, have high ouabain affinity (EC(50) ≈ 10-20 nM). We used immunoblotting, immunocytochemistry, and Ca(2+) imaging (fura-2) to examine the expression, distribution, and function of Na(+) pump α-subunit isoforms in human arteries and primary cultured human ASMCs (hASMCs). hASMCs express α(1)- and α(2)-Na(+) pumps. Further, α(2)-, but not α(1)-, pumps are confined to plasma membrane microdomains adjacent to sarcoplasmic reticulum (SR), where they colocalize with Na/Ca exchanger-1 (NCX1) and C-type transient receptor potential-6 (receptor-operated channels, ROCs). Prolonged inhibition (72 h) with 100 nM ouabain (blocks nearly all α(1)- and α(2)-pumps) was toxic to most cultured hASMCs. Treatment with 10 nM ouabain (72 h), however, increased NCX1 and sarco(endo)plasmic reticulum Ca(2+)-ATPase expression and augmented ATP (10 μM)-induced SR Ca(2+) release in 0 Ca(2+), ouabain-free media, and Ca(2+) influx after external Ca(2+) restoration. The latter was likely mediated primarily by ROCs and store-operated Ca(2+) channels. These hASMC protein expression and Ca(2+) signaling changes are comparable with previous observations on myocytes isolated from arteries of many rat hypertension models. We conclude that the same structurally and functionally coupled mechanisms (α(2)-Na(+) pumps, NCX1, ROCs, and the SR) regulate Ca(2+) homeostasis and signaling in hASMCs and rodent ASMCs. These ouabain/endogenous ouabain-modulated mechanisms underlie the whole body autoregulation associated with increased vascular resistance and elevation of BP in human, salt-sensitive hypertension.
authors: Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors: Cristina I
authors: CI
authors: Linde
authors: Laura K
authors: LK
authors: Antos
authors: Vera A
authors: VA
authors: Golovina
authors: Mordecai P
authors: MP
authors: Blaustein
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D015153:Blotting, Western; D020013:Calcium Signaling / Q000187:drug effects*; D002298:Cardenolides / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D048430:Cell Shape / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005260:Female; D006706:Homeostasis; D006801:Humans; D006973:Hypertension / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D007150:Immunohistochemistry; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008323:Mammary Arteries / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology*; D051381:Rats; D012503:Saponins / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology* / Q000633:toxicity; D019831:Sodium-Calcium Exchanger / Q000187:drug effects* / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D050052:TRPC Cation Channels / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D015854:Up-Regulation; D014655:Vascular Resistance / Q000187:drug effects*; D055815:Young Adult
chemical_list: D002298:Cardenolides; D053496:Inositol 1,4,5-Trisphosphate Receptors; D012503:Saponins; D019831:Sodium-Calcium Exchanger; D050052:TRPC Cation Channels; C034504:digoxin-like factors; C110374:sodium-calcium exchanger 1; D012965:Sodium Chloride; D010042:Ouabain; C499076:ATP1A1 protein, human; C498531:ATP1A2 protein, human; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506946:ATP2A2 protein, human; D000254:Sodium-Potassium-Exchanging ATPase