L-type voltage-dependent Ca2+ and ATP-sensitive K+ channels are not involved in the regulation of bovine ciliary muscle contractility.
We compared the effects of L-type voltage-dependent Ca2+ and ATP-sensitive K+ channels modulators on contractility in isolated bovine ciliary muscle with those in rabbit aortae. Nifedipine (0.1 and 1 microM), a dihydropyridine Ca2+ channel blocker, did not relax bovine ciliary muscle precontracted with 100 mM KCl. Nondihydropyridine Ca2+ channel blockers, semotiadil fumarate (SD-3211, 1 microM) diltiazem (10 microM) and verapamil (1 microM), did not affect contractility, but at higher concentrations, they all had a relaxant effect. Bay K 8644, a L-type voltage-dependent Ca2+ channel activator, even at 1 microM, did not contract ciliary muscle partially depolarized with 10 mM KCl, whereas at 0.01 and 0.1 microM it contracted partially depolarized rabbit aortae. Furthermore, diazoxide (100 microM), an ATP-sensitive K+ channel opener, had a relaxant effect on aortae precontracted with 25 mM KCl, but not on ciliary muscle. This relaxation was inhibited by glibenclamide (10 microM), an ATP-sensitive K+ channel blocker, indicating that diazoxide relaxes rabbit aortae by activating ATP-sensitive K+ channels. These results suggest that L-type voltage-dependent Ca2+ and ATP-sensitive K+ channels play a minor role in the regulation of bovine ciliary muscle contractility.
Kageyama
M
M
Central Research Laboratories, Santen Pharmaceutical Co., Ltd., Osaka, Japan.
Shirasawa
E
E
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001013:Aorta, Thoracic; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002417:Cattle; D002924:Ciliary Body / Q000187:drug effects / Q000378:metabolism*; D003981:Diazoxide / Q000494:pharmacology; D004594:Electrophysiology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D014665:Vasodilator Agents / Q000494:pharmacology
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D015221:Potassium Channels; D014665:Vasodilator Agents; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D003981:Diazoxide; D002118:Calcium