Characteristics of the Ca2+ pump and Ca2+-ATPase in the plasma membrane of rat myometrium.

A. Enyedi, J. Minami, A. J. Caride, J. T. Penniston

Research output: Contribution to journalArticle

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Abstract

A plasma membrane-enriched fraction from rat myometrium shows ATP-Mg2+-dependent active calcium uptake which is independent of the presence of oxalate and is abolished by the Ca2+ ionophore A23187. Ca2+ loaded into vesicles via the ATP-dependent Ca2+ uptake was released by extravesicular Na+. This showed that the Na+/Ca2+ exchange and the Ca2+ uptake were both occurring in plasma membrane vesicles. In a medium containing KCl, vanadate readily inhibited the Ca2+ uptake (K1/2 5 microM); when sucrose replaced KCl, 400 microM-vanadate was required for half inhibition. Only a slight stimulation of the calcium pump by calmodulin was observed in untreated membrane vesicles. Extraction of endogenous calmodulin from the membranes by EGTA decreased the activity and Ca2+ affinity of the calcium pump; both activity and affinity were fully restored by adding back calmodulin or by limited proteolysis. A monoclonal antibody (JA3) directed against the human erythrocyte Ca2+ pump reacted with the 140 kDa Ca2+-pump protein of the myometrial plasma membrane. The Ca2+-ATPase activity of these membranes is not specific for ATP, and is not inhibited by mercurial agents, whereas Ca2+ uptake has the opposite properties. Ca2+-ATPase activity is also over 100 times that of calcium transport; it appears that the ATPase responsible for transport is largely masked by the presence of another Ca2+-ATPase of unknown function. Measurements of total Ca2+-ATPase activity are, therefore, probably not directly relevant to the question of intracellular Ca2+ control.

Original languageEnglish
Pages (from-to)215-220
Number of pages6
JournalBiochemical Journal
Volume252
Issue number1
Publication statusPublished - May 15 1988

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Calcium-Transporting ATPases
Myometrium
Cell membranes
Rats
Calmodulin
Cell Membrane
Pumps
Calcium
Vanadates
Adenosine Triphosphate
Membranes
Proteolysis
Oxalates
Egtazic Acid
Ionophores
Calcimycin
Adenosine Triphosphatases
Sucrose
Erythrocytes
Monoclonal Antibodies

ASJC Scopus subject areas

  • Biochemistry

Cite this

Characteristics of the Ca2+ pump and Ca2+-ATPase in the plasma membrane of rat myometrium. / Enyedi, A.; Minami, J.; Caride, A. J.; Penniston, J. T.

In: Biochemical Journal, Vol. 252, No. 1, 15.05.1988, p. 215-220.

Research output: Contribution to journalArticle

Enyedi, A, Minami, J, Caride, AJ & Penniston, JT 1988, 'Characteristics of the Ca2+ pump and Ca2+-ATPase in the plasma membrane of rat myometrium.', Biochemical Journal, vol. 252, no. 1, pp. 215-220.
Enyedi, A. ; Minami, J. ; Caride, A. J. ; Penniston, J. T. / Characteristics of the Ca2+ pump and Ca2+-ATPase in the plasma membrane of rat myometrium. In: Biochemical Journal. 1988 ; Vol. 252, No. 1. pp. 215-220.
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