In the present study, the effect of tetramethylpyrazine (TMP) on calcium (Ca2+) influx was investigated in cultured vascular smooth muscle (A7r5) cells using Fura-2 as an indicator. The increase of Ca2+ concentration in A7r5 cells produced by vasopressin or phenylephrine was attenuated by TMP from 0.01 μmol/L to 1 mmol/L. The decrease in the intracellular potassium concentration in A7r5 cells by TMP from 0.01 μmol/L to 10 μmol/L was characterized using PBFI/AM. Inhibitors specific to the small conductance calcium-activated potassium (SKCa) channel or the ATP-sensitive potassium (KATP) channel abolished the actions of TMP. The obtained results indicate that the decrease of Ca2+ influx into A7r5 cells by TMP is mainly mediated by the opening of potassium channels.
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