Capacitative Ca2+ entry and the regulation of smooth muscle tone.
In many non-excitable cells, activation of phospholipase C-linked receptors results in a biphasic increase in the cytosolic Ca2+ concentration; an initial transient increase, owing to the release of Ca2+ from the endoplasmic/sarcoplasmic reticulum (ER/SR), is followed by a much smaller but sustained elevation, which often involves capacitative Ca2+ entry, where depletion of Ca2+ within the ER signals the opening of store-operated Ca2+ channels in the plasma membrane. However, in excitable cells such as smooth muscle, the role of capacitative Ca2+ entry is less clear and the main Ca2+ entry mechanisms responsible for sustained cellular activation have been considered to be either voltage-operated or receptor-operated Ca2+ channels. Although store-regulated Ca2+ entry was known to occur following agonist activation of smooth muscle, it was believed to be important only for the re-filling of the depleted SR and not as a source of activator Ca2+ for the contractile mechanisms. Here, Alan Gibson, Ian McFadzean, Pat Wallace and Christopher Wayman review recent evidence that capacitative Ca2+ entry might indeed be important for the regulation of smooth muscle tone, and that it might provide an important for pharmacological intervention.
Gibson
A
A
Biomedical Sciences Division, King's College London, UK.
McFadzean
I
I
Wallace
P
P
Wayman
C P
CP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D002121:Calcium Channel Blockers; D000252:Calcium-Transporting ATPases; D002118:Calcium