Cellular target of voltage and calcium-dependent K(+) channel blockers involved in EDHF-mediated responses in rat superior mesenteric artery.
1. We have investigated the cellular target of K(+) channel blockers responsible for the inhibition of the EDHF-mediated relaxation in the rat mesenteric artery by studying their effects on tension, smooth muscle cell (SMC) membrane potential and endothelial cell Ca(2+) signal ([Ca(2+)](endo)). 2. In arteries contracted with prostaglandin F(2 alpha) (2.5 - 10 microM), relaxation evoked by ACh (0.01 - 3 microM) was abolished by a combination of charybdotoxin (ChTX, 0.1 microM) plus apamin (Apa, 0.1 microM) and was inhibited by 68+/-6% (n=6) by 4-aminopyridine (4-AP, 5 mM). 3. ACh(0.001 - 3 microM) increased [Ca(2+)](endo) and hyperpolarized SMCs with the same potency, the pD(2) values were equal to 7.2+/-0.08 (n=4) and 7.2+/-0.07 (n=9), respectively. SMCs hyperpolarization to ACh (1 microM) was abolished by high K(+) solution or by ChTX/Apa. It was decreased by 66+/-5% (n=6) by 4-AP. 4. The increase in [Ca(2+)](endo) evoked by ACh (1 microM) was insensitive to ChTX/Apa but was depressed by 58+/-16% (n=6) and 27+/-4% (n=7) by raising external K(+) concentration and by 4-AP, respectively. 5. The effect of 4-AP on [Ca(2+)](endo) was not affected by increasing external K(+) concentration. In Ca-free/EGTA solution, the transient increase in [Ca(2+)](endo) evoked by ACh (1 microM) was abolished by thapsigargin (1 microM) and was decreased by 75+/-7% (n=5) by 4-AP. 6. These results show that inhibition of EDHF-evoked responses by 4-AP may be attributed to a decrease in the Ca(2+) release activated by ACh in endothelial cells. The abolition of SMCs hyperpolarization to ACh by ChTX/Apa is not related to an interaction with the [Ca(2+)](endo).
Ghisdal
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P
Laboratoire de Pharmacologie, Université Catholique de Louvain, UCL 5410, Avenue Hippocrate, 54 - B 1200 Bruxelles, Belgium.
Morel
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N
D015761:4-Aminopyridine / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001685:Biological Factors / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D018999:Charybdotoxin / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects*; D017538:Mesenteric Artery, Superior / Q000187:drug effects* / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors* / Q000502:physiology; D051381:Rats; D011921:Rats, Inbred WKY; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology
D001685:Biological Factors; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D014665:Vasodilator Agents; C067410:endothelium-dependent hyperpolarization factor; D018999:Charybdotoxin; D001030:Apamin; D015761:4-Aminopyridine; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium