Transient receptor potential channel 6-mediated, localized cytosolic [Na+] transients drive Na+/Ca2+ exchanger-mediated Ca2+ entry in purinergically stimulated aorta smooth muscle cells.
The Na+/Ca2+ exchanger (NCX) is increasingly recognized as a physiological mediator of Ca2+ influx and significantly contributes to salt-sensitive hypertension. We recently reported that Ca2+ influx by the NCX (1) is the primary mechanism of Ca2+ entry in purinergically stimulated rat aorta smooth muscle cells and (2) requires functional coupling with transient receptor potential channel 6 nonselective cation channels. Using the Na+ indicator CoroNa Green, we now directly observed and characterized the localized cytosolic [Na+] ([Na+]i) elevations that have long been hypothesized to underlie physiological NCX reversal but that have never been directly shown. Stimulation of rat aorta smooth muscle cells caused both global and monotonic [Na+]i elevations and localized [Na+]i transients (LNats) at the cell periphery. Inhibition of nonselective cation channels with SKF-96365 (50 micromol/L) and 2-amino-4-phosphonobutyrate (75 micromol/L) reduced both global and localized [Na+]i elevations in response to ATP (1 mmol/L). This effect was mimicked by expression of a dominant negative construct of transient receptor potential channel 6. Selective inhibition of NCX-mediated Ca2+ entry with KB-R7943 (10 micromol/L) enhanced the LNats, whereas the global cytosolic [Na+] signal was unaffected. Inhibition of mitochondrial Na+ uptake with CGP-37157 (10 micromol/L) increased both LNats and global cytosolic [Na+] elevations. These findings directly demonstrate NCX regulation by LNats, which are restricted to subsarcolemmal, cytoplasmic microdomains. Analysis of the LNats, which facilitate Ca2+ entry via NCX, suggests that mitochondria limit the cytosolic diffusion of LNats generated by agonist-mediated activation of transient receptor potential channel 6-containing channels.
Poburko
Damon
D
Department of Anesthesiology, Pharmacology & Therapeutics, University of British Columbia, Vancouver, Canada, V6T 1Z1.
Liao
Chiu-Hsiang
CH
Lemos
Virginia S
VS
Lin
Eric
E
Maruyama
Yoshiaki
Y
Cole
William C
WC
van Breemen
Cornelis
C
D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000166:cytology; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D006973:Hypertension / Q000378:metabolism / Q000503:physiopathology*; D008928:Mitochondria / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D050052:TRPC Cation Channels / Q000235:genetics / Q000378:metabolism*; D000074287:TRPC6 Cation Channel; D014162:Transfection
D019831:Sodium-Calcium Exchanger; D050052:TRPC Cation Channels; D000074287:TRPC6 Cation Channel; C117032:TRPC6 protein, human; C110374:sodium-calcium exchanger 1; D000255:Adenosine Triphosphate; D012964:Sodium; D002118:Calcium