P. Pacaud et G. Loirand, RELEASE OF CA2-VEIN MYOCYTES( BY NORADRENALINE AND ATP FROM THE SAME CA2+ STORE SENSITIVE TO BOTH INSP(3) AND CA2+ IN RAT PORTAL), Journal of physiology, 484(3), 1995, pp. 549-555
1. Changes in cytosolic free Ca2+ concentration ([Ca2+](i)) induced by
noradrenaline (NA) and ATP were investigated using indo-1 microspectr
ofluorimetry in single smooth muscle cells of rat portal vein. 2. Acti
vation of P-2x-purinoceptors by ATP (10 mu M) increased [Ca2+](i) from
92 +/- 7 nM (n = 18) to 557 +/- 30 nM (n = 11). In the presence of NS
(10 mu M), the ATP-induced rise in [Ca2+](i) was reduced to 23.6 +/-
1.5% (n = 7) of the control response (in the absence of NA). 3. Tetrac
aine (10 mu M to 2 mM) inhibited in a concentration-dependent manner t
he Ca2+-induced Ca2+ release (CICR) evoked by 5 mM caffeine. In the pr
esence of 1 mM tetracaine, the rise in [Ca2+](i) induced by ATP (10(-8
)-10(-4) M) was strongly inhibited. A tetracaine-resistant rise in [Ca
2+](i), corresponding to 26.4 +/- 2.3% (n = 14) of control values, was
recorded in response to 10 mu M ATP. 4. The amplitude of the NA-induc
ed [Ca2+](i) rise depended on NE concentrations (10(-8)-10(-5) M) and
was not modified by tetracaine (1 mM). 5. This study suggests that Ca2
+ ions released through the InsP(3) receptor-channel upon NA applicati
on do not activate CICR and that the InsP(3)- and Ca2+-sensitive Ca2store appears to represent, at least functionally, a single releasable
Ca2+ pool.