Influence of extracellular Na+ removal on cytosolic Ca2+ concentration in smooth muscle cells of rabbit cerebral artery.
There are some controversies over the contribution of Na+/Ca2+ exchanger (NCX) to the regulation of cytosolic Ca2+ concentration ([Ca2+]c) in smooth muscle. To prove the functional role of Na+/Ca2+ exchanger, we examined whether the removal of extracelluar Na+ could affect [Ca2+]c of rabbit cerebral arterial smooth muscle. The fluorescence ratio of fura-2 (R(340/380)) was measured in the single myocyte of rabbit middle cerebral artery and Na+ was substituted with the same concentration of NMDG+ or Li+. In 21 out of 230 cells tested, Na+ removal increased R(340,380) (deltaR(340/380)) by 115 +/- 16.5% of the deltaR(340/380) induced by 10 mM caffeine in the same cell. The Na+ removal-induced deltaR(340/380) was blocked by a selective inhibitor of cardiac type NCX exchanger (KB-R7943, (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea, 10 microM). In those cells where the Na+ removal by itself did not increase R(340/380), the caffeine-induced deltaR(340/380) was increased by Na+-removal (130 +/- 9.8% of control response, n=30). Under the whole-cell patch clamp condition, short application of caffeine induced transient increase of outward current (I(K,Ca)-transient) which reflect the change of subsarcolemmal [Ca2+]. The application of KB-R7943 increased the amplitude of I(K,Ca)-transient (n=4). These results suggest the functional existence of NCX in rabbit cerebral artery smooth muscle.
Kim
J K
JK
Department of Physiology & Biophysics, Seoul National University College of Medicine, Chongno-Gu, Korea.
Kim
S J
SJ
Kim
Y C
YC
So
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Kim
K W
KW
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol; D020768:Middle Cerebral Artery / Q000166:cytology / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / 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; D015221:Potassium Channels; D019831:Sodium-Calcium Exchanger; D002110:Caffeine; D012964:Sodium; D013890:Thiourea; D002118:Calcium