Abstract
BDM, a chemical phosphatase commonly used to suppress muscle contraction, is often used for isolating single heart cells as an easy relief for ischemic damages. However, BDM is also known to interfere with the intracellular protein phosphorylation, and to modify calcium signaling by suppressing Ca channels and Na/Ca exchangers in heart cells. In mouse heart cells, where BDM is most oftenly used for cell isolation, the action of BDM on intracellular signaling pathways and ion channels/transporters still remains unknown. We therefore examined the effect of BDM on calcium current in whole-cell clamped mouse heart cells to survey how BDM affects Ca channels and their regulation via the well-established signaling pathway via PKA. Our results show: 1) when applied extracellularly, BDM decreased the amplitude of calcium current in a dose-dependent manner (K1/2=7.3 mM, nH=1.33); 2) at the same time, BDM shifted the peak of the I-V relation to more depolarized potential; 3) also, BDM had no significant effect on the dose-response relation of calcium current to isoproterenol; 4) when applied intracellularly, BDM had very little effect on ICa amplitude. These lines of evidence indicate that BDM inhibits cardiac calcium current by blocking Ca channels; although involvement of its action as chemical phosphatase cannot be ruled out. BDM is reportedly useful for heart cell isolation and culture, it may alter the electrophysiological properties of the cells. [Jpn J Physiol 55 Suppl:S135 (2005)]
