The duration and amplitude of the plateau phase of ATP- and ADP-evoked Ca(2+) signals are modulated by ectonucleotidases in in situ endothelial cells of rat aorta.
ATP has a long-lasting vasodilatory effect, possibly due to its capability to induce a prolonged increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) in endothelial cells (EC) and activate constitutive nitric oxide synthase. However, contradictory data have been reported regarding the time course of ATP-evoked Ca(2+) signals in in situ EC. In particular, short-duration Ca(2+) signals have been reported, which might be thought to be unable to sustain a prolonged, NO-induced vasodilation. The current experiments were therefore performed in in situ EC of rat aorta in order to more fully define the time course of ATP-evoked Ca(2+) signals. 20 microM ATP evoked a short-lasting Ca(2+) signal. However, medium stirring, high agonist concentrations, inhibition of ectonucleotidases and application of a poorly hydrolyzable agonist evoked long-lasting Ca(2+) signals (up to 20 min at 37 degrees C). These studies suggest that ATP is able to sustain a prolonged [Ca(2+)](i) increase, unless ectonucleotidase activity reduces the agonist concentration near the EC surface to subthreshold values, quickly cutting the Ca(2+) signal. Furthermore, the amplitude of the long-lasting phase of the Ca(2+) signal depended on the balance between agonist degradation by ectonucleotidases and agonist transport, by diffusion and convection, from bulk solution to the EC surface.
Department of Physiological and Pharmacological Sciences, University of Pavia, Pavia, Italy.
Roberto
R
Berra-Romani
Chiara
C
Rinaldi
Abdul
A
Raqeeb
Loretta
L
Castelli
Jacopo
J
Magistretti
Vanni
V
Taglietti
Franco
F
Tanzi
D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000201:enzymology*; D020013:Calcium Signaling / Q000187:drug effects*; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology*; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D051381:Rats; D017208:Rats, Wistar; D013696:Temperature
D005456:Fluorescent Dyes; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C027201:ectoATPase; D016257:Fura-2