Role of basal extracellular Ca2+ entry during 5-HT-induced vasoconstriction of canine pulmonary arteries.
1. Measurements of artery contraction, cytosolic [Ca(2+)], and Ca(2+) permeability were made to examine contractile and cytosolic [Ca(2+)] responses of canine pulmonary arteries and isolated cells to 5-hydroxytryptamine (5-HT), and to determine the roles of intracellular Ca(2+) release and extracellular Ca(2+) entry in 5-HT responses. 2. The EC(50) for 5-HT-mediated contractions and cytosolic [Ca(2+)] increases was approximately 10(-7) M and responses were inhibited by ketanserin, a 5-HT(2A)-receptor antagonist. 3. 5-HT induced cytosolic [Ca(2+)] increases were blocked by 20 microM Xestospongin-C and by 2-APB (IC(50)=32 microM inhibitors of InsP(3) receptor activation. 4. 5-HT-mediated contractions were reliant on release of InsP(3) but not ryanodine-sensitive Ca(2+) stores. 5. 5-HT-mediated contractions and cytosolic [Ca(2+)] increases were partially inhibited by 10 microM nisoldipine, a voltage-dependent Ca(2+) channel blocker. 6. Extracellular Ca(2+) removal reduced 5-HT-mediated contractions further than nisoldipine and ablated cytosolic [Ca(2+)] increases and [Ca(2+)] oscillations. Similar to Ca(2+) removal, Ni(2+) reduced cytosolic [Ca(2+)] and [Ca(2+)] oscillations. 7. Mn(2+) quench of fura-2 and voltage-clamp experiments showed that 5-HT failed to activate any significant voltage-independent Ca(2+) entry pathways, including store-operated and receptor-activated nonselective cation channels. Ni(2+) but not nisoldipine or Gd(3+) blocked basal Mn(2+) entry. 8. Voltage-clamp experiments showed that simultaneous depletion of both InsP(3) and ryanodine-sensitive intracellular Ca(2+) stores activates a current with linear voltage dependence and a reversal potential consistent with it being a nonselective cation channel. 5-HT did not activate this current. 9. Basal Ca(2+) entry, rather than CCE, is important to maintain 5-HT-induced cytosolic [Ca(2+)] responses and contraction in canine pulmonary artery.
Wilson
Sean M
SM
Department of Pharmacology, University of Nevada School of Medicine, Reno, MS 318, NV 89557, USA.
Mason
Helen S
HS
Ng
Lih C
LC
Montague
Stephen
S
Johnston
Louise
L
Nicholson
Neil
N
Mansfield
Sarah
S
Hume
Joseph R
JR
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D045604:Extracellular Fluid / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D011651:Pulmonary Artery / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology*; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
D012701:Serotonin; D002118:Calcium