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.
Berra-Romani
Roberto
R
Department of Physiological and Pharmacological Sciences, University of Pavia, Pavia, Italy.
Rinaldi
Chiara
C
Raqeeb
Abdul
A
Castelli
Loretta
L
Magistretti
Jacopo
J
Taglietti
Vanni
V
Tanzi
Franco
F
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