Nitric oxide derived from endothelial cells inhibits Na+/H+ exchange in rabbit platelets activated by thrombin.
OBJECTIVE
To study the effect of nitric oxide (NO) derived from endothelial cells on Na+/H+ exchange in rabbit platelets activated by thrombin.


METHODS
Intracellular Ca2+ ([Ca2+]i) and intracellular pH (pHi) were measured by the dual-wavelength fluorophotometer with the fluorescent probes Fura-2 and 2',7'-biscarboxyethyl-5,6-carboxyfluorescein (BCECF). Effects of NO on rabbit platelets were tested by cultured bovine endothelial cells (BAEC).


RESULTS
BAEC (0.1-1 x 10(9).L-1) inhibited thrombin (100 U.L-1)-induced platelet aggregation in a concentration-dependent manner. This inhibiting effect was abolished by preincubating BAEC with NG-nitro-L-arginine 1 mmol.L-1. When the [Ca2+]i store was depleted with ionomycin in the presence of egtazic acid (EGTA), the increase in pHi induced by thrombin was inhibited. Refilling intracellular Ca2+ store partially reversed this effect. BAEC 2 x 10(8).L-1 inhibited thrombin (100 U.L-1)-induced elevation of pHi and mobilization of intracellular Ca2+ store (P < 0.01). No direct effect of endothelial cells on unstimulated rabbit platelets was observed.


CONCLUSIONS
NO derived from endothelial cells inhibited thrombin-induced rabbit platelet activation by inhibiting thrombin-induced [Ca2+]i mobilization and then inhibiting the consequent Na+/H+ exchange in rabbit platelets.
Chen
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Laboratory of Molecular Pharmacology, Hunan Medical University, Changsha, China. chgd@hotmail.com
Guo
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ZG
D000818:Animals; D001013:Aorta, Thoracic; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D004730:Endothelium, Vascular / Q000737:chemistry; D005260:Female; D008297:Male; D009569:Nitric Oxide / Q000302:isolation & purification / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D052250:Nitric Oxide Synthase Type III; D019335:Nitroarginine / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011817:Rabbits; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology
D010975:Platelet Aggregation Inhibitors; D017923:Sodium-Hydrogen Exchangers; D019335:Nitroarginine; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D013917:Thrombin; D002118:Calcium