Article date: December 2000
By: E Spitzbarth‐Régrigny, M ‐A Petitcolin, J ‐L Bueb, E J Tschirhart, J Atkinson, C Capdeville‐Atkinson in Volume 131, Issue 7, pages 1337-1344
We studied the involvement of pertussis toxin (PTX)‐sensitive G‐proteins in the sensitivity of arterial constriction to intracellular calcium ([Ca2+]i) mobilization.
Vasoconstriction was measured in vitro in perfused, de‐endothelialized rat tail arteries loaed with the calcium‐sensitive dye, fura‐2 and treated or not with PTX (30–1000 ng ml−1). Arteries were stimulated with noradrenaline (NA, 0.1–100 μM) or KCl (15–120 mM).
KCl elicited a smaller vasoconstrictor response (Emax=94±8 mmHg) than NA (Emax=198±9 mmHg) although [Ca2+]i mobilization was similar (Emax=123±8 and 135±7 nM for KCl and NA, respectively). PTX (1000 ng ml−1) had no effect on [Ca2+]i mobilization but lowered NA‐ (but not KCl‐) induced vasoconstriction (Emax=118±7 mmHg).
Gi/o‐proteins were revealed by immunoblotting with anti‐Giα and anti‐Goα antibodies in membranes prepared from de‐endothelialized tail arteries. [α32P]‐ADP‐ribosylation of G‐proteins by PTX (1000 ng ml−1) was demonstrated in the intact rat tail artery (pixels in the absence of PTX: 3150, presence: 25053).
In conclusion, we suggest that smooth muscle cells possess a PTX‐sensitive Gi‐protein‐mediated intracellular pathway which amplifies [Ca2+]i sensitivity of contraction in the presence of agonists such as NA.
We studied the involvement of pertussis toxin (PTX)‐sensitive G‐proteins in the sensitivity of arterial constriction to intracellular calcium ([Ca2+]i) mobilization.
Vasoconstriction was measured in vitro in perfused, de‐endothelialized rat tail arteries loaed with the calcium‐sensitive dye, fura‐2 and treated or not with PTX (30–1000 ng ml−1). Arteries were stimulated with noradrenaline (NA, 0.1–100 μM) or KCl (15–120 mM).
KCl elicited a smaller vasoconstrictor response (Emax=94±8 mmHg) than NA (Emax=198±9 mmHg) although [Ca2+]i mobilization was similar (Emax=123±8 and 135±7 nM for KCl and NA, respectively). PTX (1000 ng ml−1) had no effect on [Ca2+]i mobilization but lowered NA‐ (but not KCl‐) induced vasoconstriction (Emax=118±7 mmHg).
Gi/o‐proteins were revealed by immunoblotting with anti‐Giα and anti‐Goα antibodies in membranes prepared from de‐endothelialized tail arteries. [α32P]‐ADP‐ribosylation of G‐proteins by PTX (1000 ng ml−1) was demonstrated in the intact rat tail artery (pixels in the absence of PTX: 3150, presence: 25053).
In conclusion, we suggest that smooth muscle cells possess a PTX‐sensitive Gi‐protein‐mediated intracellular pathway which amplifies [Ca2+]i sensitivity of contraction in the presence of agonists such as NA.
British Journal of Pharmacology (2000) 131, 1337–1344; doi:10.1038/sj.bjp.0703703
DOI: 10.1038/sj.bjp.0703703
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