The alpha 1-agonist phenylephrine inhibits voltage-gated Ca2(+)-channels in vascular smooth muscle cells of rabbit ear artery.
The effects of the alpha 1-agonist phenylephrine on the voltage-gated Ca2(+)-entry in vascular smooth muscle cells has been studied by measuring the agonist-induced changes of [Ca2+]i in K(+)-depolarized tissues. These changes have been estimated from the changes in fluorescence of the Ca2(+)-indicator fura-2, or have been assessed from the changes in 86Rb-efflux rate through Ca2(+)-activated K(+)-channels. Phenylephrine increases the force development in K(+)-depolarized tissues, but reduces [Ca2+]i and inhibits the 86Rb-efflux rate. However, in the presence of the Ca2(+)-entry blocker verapamil, phenylephrine increases both force development and [Ca2+]i. It is concluded that phenylephrine inhibits voltage-gated Ca2(+)-channels, and also induces an influx of calcium by activating a verapamil-insensitive pathway.
Declerck
I
I
Laboratorium voor Fysiologie, Campus Gasthuisberg, KU Leuven, Belgium.
Himpens
B
B
Droogmans
G
G
Casteels
R
R
D000818:Animals; D001158:Arteries / Q000166:cytology / Q000378:metabolism; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D004423:Ear / Q000098:blood supply*; D005260:Female; D016257:Fura-2; D015640:Ion Channel Gating / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects / Q000648:ultrastructure; D010656:Phenylephrine / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011817:Rabbits; D012414:Rubidium Radioisotopes; D014700:Verapamil / Q000494:pharmacology
D015220:Calcium Channels; D015221:Potassium Channels; D012414:Rubidium Radioisotopes; D010656:Phenylephrine; D014700:Verapamil; D011188:Potassium; D002118:Calcium; D016257:Fura-2