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Mg 2+ ‐Dependent Modulation of BK Ca Channels by Genistein in Rat Arteriolar Smooth Muscle Cells
Author(s) -
Wang Xiaoran,
Zhao Tingting,
Zhou Shanshan,
Sun Lina,
Zhang Liming,
Yu Guichun
Publication year - 2014
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.24648
Subject(s) - genistein , sodium orthovanadate , chemistry , patch clamp , intracellular , biophysics , tyrosine kinase inhibitor , tyrosine kinase , endocrinology , protein tyrosine phosphatase , tyrosine , biochemistry , medicine , signal transduction , biology , receptor , cancer
Genistein, a protein tyrosine kinase (PTK) inhibitor, regulates ion channel activities. However, the mechanism of action of genistein on large‐conductance calcium‐activated potassium (BK Ca ) channels is unclear. This study aimed to investigate whether the mechanism of Mg 2+ ‐dependent modulation of BK Ca channel activity in vascular smooth muscle cells involved inhibition of phosphorylation by genistein or direct interaction between genistein and BK Ca channels. The whole‐cell and inside‐out patch‐clamp techniques were used to measure BK Ca currents and the effects of genistein on BK Ca channel activities in rat mesenteric arteriolar smooth muscle cells. We found that the effects of genistein on BK Ca currents were Mg 2+ ‐dependent. Genistein (50 μM) inhibited BK Ca currents if the intracellular free magnesium concentration ([Mg 2+ ] i ) was 2 μM or 20 μM, but amplified BK Ca currents if [Mg 2+ ] i was 200 μM or 2000 μM. The inhibitory effect of genistein on BK Ca currents was reversed by the protein tyrosine phosphatase inhibitor sodium orthovanadate (0.5 mM). Daidzein (50 μM), an inactive analogue of genistein, also amplified BK Ca currents, and its amplification was insensitive to orthovanadate. Another PTK inhibitor, tyrphostin 23 (50 μM), reduced the open probability of BK Ca channels. This inhibitory effect was weaker at 200 μM [Mg 2+ ] i than at 2 μM [Mg 2+ ] i , and was countered by orthovanadate. Our results suggest that genistein amplifies BK Ca currents at a high [Mg 2+ ] i , but inhibits BK Ca currents at a low [Mg 2+ ] i . The mechanism of this biphasic effects involves PTK‐independent amplification and [Mg 2+ ] i ‐PTK‐dependent inhibition. J. Cell. Physiol. 229: 1981–1989, 2014. © 2014 Wiley Periodicals, Inc.