An Estrogen Metabolite, 2-Methoxyestradiol, Disrupts Cardiac Microtubules and Unmasks Muscarinic Inhibition of Calcium Current

Abstract

Microtubules provide a chemical signaling function as well as structural support for heart cells. Microtubules modulate autonomic signaling in the heart, and their disruption by colchicine unmasks muscarinic inhibition of Ca (I_Ca) current. In this study, we compare the actions of the estrogen metabolite, 2-methoxyestradiol (2-ME), with those of colchicine on microtubule stability and chemical signal function in guinea pig-isolated ventricular myocytes. Like colchicine, 2-ME binds to microtubules and disrupts the cytoskeleton of cardiac myocytes. Incubation with 2-ME increased the soluble fraction of tubulin and decreased the polymerized fraction at concentrations ranging from 10 to 100 μM. 2-ME was less potent than colchicine in causing microtubular disruption. Treatment with 2-ME for up to 4 h was accompanied by a progressive increase of I_Ca amplitude. There was no change in the rates of I_Ca inactivation. Carbachol, which has no effect on I_Ca in untreated ventricular myocytes, inhibited this current in the presence of 2-ME. The extent of inhibition increased with incubation time in 2-ME such that carbachol completely removed the increment of I_Ca by the estrogen metabolite. The results illustrate the important role of microtubules in modulating cardiac autonomic signaling.