Fatty acid modifies Ca ²⁺ -dependent potassium channel activity in smooth muscle cells from the human aorta

By using the patch-clamp technique the effect of 2-decenoic acid (DA) on Ca$^{2+}$-activated potassium (K$^+$) channels in the membrane of smooth muscle cells from the human aorta was studied. In the presence of 0.5 $\mu M$ Ca$^{2+}$ and 2 mM Mg$^{2+}$ on the cytoplasmic side of the membrane, a more than tenfold elevation in the probability of the channels being open (p$_o$) was observed under the effect of DA. With divalent cation concentrations of less than 1 nM DA caused a more than twofold elevation in p$_o$. In the DA-treated membranes Mg$^{2+}$ ions, which normally fail to activate the channels, brought about a nearly threefold increase in the channel activity when applied to the inner membrane surface. Channel sensitivity to the activating effect of cytoplasmic Ca$^{2+}$ ions did not increase with the application of DA. Single-channel conductance was unchanged by DA exposure. We suggest that DA alters the Ca$^{2+}$-binding mechanism of the channel. increasing its sensitivity to Mg$^{2+}$ ions, presumably owing to membrane fluidization.