COMPARISON OF THE CA2-ADRENOCEPTOR SUBTYPES IN HEK-293 CELLS( MOVEMENT BY ACTIVATION OF ALPHA(1))

We studied the Ca2+ movement induced by activation of alpha(1A)-, alph a(1B)- and alpha(1D)-adrenoceptor subtypes in transfected HEK-293 cell s with the fura-2 probe. All these alpha(1)-AR subtypes induced both C a2+ release and Ca2+ entry. The effect on Ca2+ release in alpha(1b) tr ansfected HEK-293 cells was bigger than that in alpha(1a) and alpha(1d ) transfected HEK-293 cells, and the effects on Ca2+ entry were the sa me in alpha(1a), alpha(1b) and alpha(1d) transfected HEK-293 cells. Th e Ca2+ entry was inhibited by 1 mM NiSO4, but not by nifedipine. Cyclo piazonic acid (CPA) produced a biphasic Ca2+ signal response in Ca2+ m edium, and only induced a transient response in Ca2+-free medium. Afte r depletion of CPA-sensitive Ca2+ pool by 10 mu M CPA in Ca2+-free med ium, 10 mu M adrenaline (Adr) still transiently increased [Ca2+](i) in three different alpha(1)-adrenoceptor subtype transfected HEK-293 cel ls. However, after depletion of adrenaline-sensitive Ca2+ pool by 10 m u M Adr, CPA transiently elevated [Ca2+](i) only in alpha(1a) and alph a(1d) transfected HEK-293 cells, not in alpha(1b) transfected HEK-293 cells. U73122, a phospholipase C (PLC) inhibitor, inhibited both Ca2release and Ca2+ entry induced by activation of alpha(1A), alpha(1B) a nd alpha(1D) subtypes in transfected HEK-293 cells. These results sugg est that HEK-293 cell line contains two functionally separate intracel lular Ca2+ pools, CPA-sensitive and Adr-sensitive pools. Activation of alpha(1B)-AR stimulates Ca2+ release from both CPA-sensitive and Adr- sensitive Ca2+ pools. alpha(1A) and alpha(1D) subtypes induce Ca2+ rel ease only from Adr-sensitive Ca2+ pool.