AlF4- induces Ca2+ oscillations in guinea-pig ileal smooth muscle.
The effects of different compounds that inhibit the isolated plasma-membrane Ca2+/Mg2(+)-ATPase on the cytosolic free Ca2+ concentration ([Ca2+]i) and on the corresponding force development have been examined in smooth muscle of the longitudinal layer of the guinea-pig ileum. F-, in the presence of Al3+, induced an increase of the resting force and of the amplitude of the superimposed phasic contractions. The increase of resting force was associated with an increased level of basal [Ca2+]i while the phasic contractions were accompanied by concomitant oscillations in [Ca2+]i. Comparable contractions could be induced by vanadate and the calmodulin antagonist calmidazolium. The oscillations of [Ca2+]i and of force elicited by AlF4- were not modified by adrenergic or cholinergic blocking agents but were inhibited by verapamil. These phasic contractions were not affected by depleting the intracellular Ca2+ stores with ryanodine. This finding excludes a cytosolic origin of these oscillations. However, hyperpolarization and complete depolarization of the cells inhibited the oscillations. It is concluded that AlF4-, vanadate and calmidazolium induce cytoplasmic Ca2+ oscillations possibly by acting at the plasma membrane. Indeed all these substances affect by different mechanisms the isolated plasma-membrane Ca2+/Mg2(+)-ATPase. The generation of membrane-linked Ca2+ oscillations could therefore be related to an inhibition of the plasma-membrane Ca2+ pump resulting in an increase of [Ca2+]i. This change in [Ca2+]i could be responsible for the pronounced changes of the electrical and mechanical activity of this tissue.
Himpens
B
B
Physiological Laboratory, K.U. Leuven, Belgium.
Missiaen
L
L
Droogmans
G
G
Casteels
R
R
D000535:Aluminum / Q000494:pharmacology*; D017607:Aluminum Compounds; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002462:Cell Membrane / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D004553:Electric Conductivity / Q000187:drug effects; D005459:Fluorides / Q000494:pharmacology*; D006168:Guinea Pigs; D007082:Ileum / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D017607:Aluminum Compounds; D002147:Calmodulin; D007093:Imidazoles; D012433:Ryanodine; D014638:Vanadates; C031938:calmidazolium; D014700:Verapamil; D000535:Aluminum; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D005459:Fluorides; D002118:Calcium; C032311:aluminum fluoride