Cardiostimulatory and antiarrhythmic activity of tubulin-binding agents.

Abstract

Rhythmic, spontaneously pulsating cardiac cells cultured from newborn rats are imediately stmulated to beat faster by addition of a number of tubulin-binding agents but not by their non-tubulin-binding an .The tubulinbinding agents tested incde vinbastine, crie, navelbine, two analogs of vinblastine (S12362 and S12363), nocodazode, colchicne, and podophylotoxin. In addi to binding tubulin, all ofthe above agents also depolymerize microtubules. Tubulin-binding agents such as colchicine, the vinca alkaloids, and benzimidazole derivatives have been extremely useful in demonstrating the large number of diverse cellular functions that depend either directly or indirectly upon the proper functioning of microtubules. These include a number of processes that involve movement-i.e., movement of cilia and flagella, movement of chromosomes, and intracellular movement of vesicles and organelles (1, 2). Although a sliding filament mechanism has been proposed to explain the role of microtubules in the movement of the above-mentioned processes, which is similar to that shown for actin in the movement involved in muscle contraction, any relationship of tubulin and/or microtubules to the mechanism of contraction of muscle remains unknown.There have been, however, three scattered reports (3-5), one of which comes from the laboratory of T.J.L. (5), suggesting that tubulin-binding agents can affect the rate of spontaneously beating cardiac cells growing in vitro (3-5).These previous reports confined their studies to one or two tubulin-binding drugs, colchicine and/or nocodazole, and thus it is not known whether other tubulin-binding agents have effects on cardiac contractility.In this study, we have addressed the hypothesis that the stimulation of cardiac muscle beating rate is a general property of tubulin-binding agents. In addition, by using taxol, a tubulin-binding compound that does not depolymerize microtubules, we have investigated whether cardiostimulation is associated with microtubule depolymerization. The physical association of tubulin with the contractile elements of cardiac muscle cells has also been studied by use of a monoclonal antibody (mAb) specific for a-tubulin. Furthermore, antiarrhythmic properties oftubulin-binding agents are presented, which opens the possibility of uncovering an additional class of antiarrhythmic drugs. MATERIALS AND METHODSEstablishment of Priary Cardiac Cultures. The procedure used here for isolating heart cells from newborn rats is a modification of that of Mark and Strasser (6) and has been described (7). Plastic plates (35-mm diameter) were seeded with 0.1-ml droplets of the primary cardiac cell suspension (2.3 x 106 cells per ml) and incubated at 3TC (5% C02/95% air) for 18 hr, at which time fresh medium (2 ml) was added to each plate. For fluorescence microscopy studies, cells were seeded on 12-mm glass coverslips. Medium changes were made every 48 hr thereafter. Drug treatments began 7 days after the cells were seeded, at which time cultures beated rhythmically and synchrono...

Microtubule Disruption Modulates Ca 2+ Signaling in Rat Cardiac Myocytes

“…Returning to the cardiac effect of microtubule disruption, it has been shown that colchicine treatment accelerates the beating frequency in neonatal cardiac cells. 14,15 This effect could also be explained by the increase in I Ca that we report. However, after shorter periods of colchicine treatment than ours, some authors did not find an effect on contraction in either control or hypertrophied myocytes.…”

Caldesmon Inhibits Nonmuscle Cell Contractility and Interferes with the Formation of Focal Adhesions

“…Microtubule disruption increases contractility in various cell types (Danowski, 1989;Lampidis et al, 1992;Kolodney and Elson, 1995;Sheridan et al, 1996;Canman and Bement, 1997). This process is accompanied by an increase of MLC phosphorylation (Kolodney and Elson, 1995) that can be a consequence of augmentation of Rho activity (Ren et al, 1999).…”

Taxol, a microtubule stabilizer, prevents ischemic ventricular arrhythmias in rats

“…Microtubule disruption can inhibit the protective effects of ischemic preconditioning and isoflurane-induced myocardial preconditioning [9, 10]. In cardiac cells from newborn rats, disruption of microtubules has been found to stimulate the rate of spontaneous contraction [11]. Tubulin-binding agents that effectively stabilize microtubules have been reported to reverse adriamycin-induced arrhythmias and to affect the probability of eliciting stretch-induced arrhythmia in rabbits [11, 12].…”