Sodium channels are required during in vivo sodium chloride hyperosmolarity to stimulate increase in intestinal endothelial nitric oxide production.
NaCl hyperosmolarity increases intestinal blood flow during food absorption due in large part to increased NO production. We hypothesized that in vivo, sodium ions enter endothelial cells during NaCl hyperosmolarity as the first step to stimulate an increase in intestinal endothelial NO production. Perivascular NO concentration ([NO]) and blood flow were determined in the in vivo rat intestinal microvasculature at rest and under hyperosmotic conditions, 330 and 380 mosM, respectively, before and after application of bumetanide (Na(+)-K(+)-2Cl(-) cotransporter inhibitor) or amiloride (Na(+)/H(+) exchange channel inhibitor). Suppressing amiloride-sensitive Na(+)/H(+) exchange channels diminished hypertonicity-linked increases in vascular [NO], whereas blockade of Na(+)-K(+)-2Cl(-) channels greatly suppressed increases in vascular [NO] and intestinal blood flow. In additional experiments we examined the effect of sodium ion entry into endothelial cells. We proposed that the Na(+)/Ca(2+) exchanger extrudes Na(+) in exchange for Ca(2+), thereby leading to the calcium-dependent activation of endothelial nitric oxide synthase (eNOS). We blocked the activity of the Na(+)/Ca(2+) exchanger during 360 mosM NaCl hyperosmolarity with KB-R7943; complete blockade of increased vascular [NO] and intestinal blood flow to hyperosmolarity occurred. These results indicate that during NaCl hyperosmolarity, sodium ions enter endothelial cells predominantly through Na(+)-K(+)-2Cl(-) channels. The Na(+)/Ca(2+) exchanger then extrudes Na(+) and increases endothelial Ca(2+). The increase in endothelial Ca(2+) causes an increase in eNOS activity, and the resultant increase in NO increases intestinal arteriolar diameter and blood flow during NaCl hyperosmolarity. This appears to be the major mechanism by which intestinal nutrient absorption is coupled to increased blood flow.
Department of Cellular and Integrative Physiology, Indiana University School of Medicine, 635 Barnhill Dr., MS 426, Indianapolis, IN 46202, USA.
Brett G
BG
Zani
H Glenn
HG
Bohlen
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000378:metabolism / Q000502:physiology; D001692:Biological Transport / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis*; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000502:physiology*; D012965:Sodium Chloride / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D015222:Sodium Channels; D019831:Sodium-Calcium Exchanger; D002034:Bumetanide; D009569:Nitric Oxide; D012965:Sodium Chloride; D000584:Amiloride; D012964:Sodium; D013890:Thiourea