A-23187 evoked transmitter release from rabbit pulmonary artery and its inhibition by reactivation of sodium-pump.
1. The spontaneous [3H]-release has been measured from the isolated main pulmonary artery of the rabbit preloaded with [3H]noradrenaline in the presence of uptake blockers (cocaine, 3 x 10(-5) M; corticosterone, 5 x 10(-5) M). 2. The Ca-ionophore A-23187 (3 x 10(-7)-3 x 10(-5) M) increased the outflow of [3H] by a concentration dependent manner. 3. Inhibition of Na+-pump by removal of K+ from the external medium also increased the release of labelled noradrenaline. 4. In the absence of external K+, the applied A-23187 (3 x 10(-6) M; EC50) further increased the release of [3H]. 5. Reactivation of Na+-pump by readmission of K+ (5.9 mM) to the external medium abolished the [3H]-release which had previously been increased in "K+-free" solution. 6. The reactivated Na+-pump significantly inhibited the transmitter releasing action of A-23187. 7. This latter was antagonized by an increase of external Ca2+ (7.5 mM). 8. It is concluded that the reactivated Na+-pump caused re-establishment of Na+-gradient is capable to counteract the Ca-ionophore facilitated Ca2+-influx and release from internal stores, which can be antagonized by excess Ca2+.
Török
T L
TL
Department of Pharmacodynamics, Semmelweis University of Medicine, Budapest, Hungary.
Rácz
D
D
Tóth
P T
PT
Azzidani
A M
AM
Powis
D A
DA
Magyar
K
K
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D011651:Pulmonary Artery / Q000187:drug effects / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*
D018377:Neurotransmitter Agents; D000001:Calcimycin; D012964:Sodium; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine