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Updated: Oct 9, 2026
Analysis of Cardiac Contractile Dysfunction and Ca2+ Transients in Rodent Myocytes
Published on: May 25, 2022
Modulation of Ca(2+) signaling by microtubule disruption in rat ventricular myocytes and its dependence on the
S C Calaghan1, J Y Le Guennec, E White
1School of Biomedical Sciences, University of Leeds, Leeds, UK.
Abstract:
In the absence of hypertrophic proliferation of microtubules, microtubule disruption by colchicine does not modulate contraction of adult cardiac myocytes. However, Gomez et al (Circ Res. 2000;86:30-36) recently reported that disruption of microtubules by colchicine in ruptured patch-clamped myocytes increased I(Ca,L) density and [Ca(2+)](i) transient amplitude and depressed the response of these parameters to the beta-adrenoceptor agonist isoproterenol. These effects were ascribed to stimulation of adenylyl cyclase by increased intracellular free tubulin. In the present study, we show that in intact rat ventricular myocytes, 2 to 4 hours of exposure to 10 micromol/L colchicine had no effect on shortening or [Ca(2+)](i) transient amplitude or on the amplitude of I(Ca,L) in perforated patch-clamped cells, under basal conditions and after stimulation with 1 micromol/L isoproterenol. However, in ruptured patch-clamped myocytes, basal I(Ca,L) was 2-fold higher after treatment with colchicine compared with vehicle and, in contrast to vehicle-treated cells, I(Ca,L) did not increase in response to isoproterenol. Cell width decreased during ruptured patch-clamp experiments in colchicine-treated but not vehicle-treated myocytes. We conclude that in cells with intact sarcolemma, colchicine does not modulate Ca(2+) signaling or the response to beta stimulation. However, the combination of microtubule disruption by colchicine and the ruptured patch configuration activates I(Ca,L) and attenuates the response to beta stimulation. We propose that these effects may be due to loss of free tubulin by intracellular dialysis or to increased sensitivity to mechanical stimulation as a result of microtubule disruption. These findings have important implications for cardiomyopathies associated with decreased free tubulin or a diminished microtubular network. The full text of this article is available at http://www.circresaha.org.
Insights
Colchicine, a microtubule disruptor, does not affect intact cardiac cells. However, it alters calcium signaling and beta-stimulation response in ruptured patch-clamped myocytes, suggesting implications for cardiomyopathies.
Area of Science:
- Cardiovascular Physiology
- Cell Biology
- Pharmacology
Background:
- Microtubules play a role in cardiac myocyte function.
- Previous studies suggested colchicine disrupts microtubules and affects calcium handling.
- The precise role of microtubules in regulating calcium currents (I(Ca,L)) and beta-adrenergic stimulation needs clarification.
Purpose of the Study:
- To investigate the effect of colchicine-induced microtubule disruption on adult rat ventricular myocytes.
- To determine if colchicine modulates calcium signaling and beta-adrenergic responses in intact and disrupted myocytes.
- To explore the mechanisms underlying colchicine's effects on I(Ca,L) and contractility.
Main Methods:
- Adult rat ventricular myocytes were treated with colchicine (10 micromol/L) for 2-4 hours.
- Electrophysiological recordings (perforated and ruptured patch-clamp) were used to measure I(Ca,L).
- Intracellular calcium transients ([Ca(2+)](i)) and cell shortening were assessed.
- Myocytes were stimulated with isoproterenol (1 micromol/L) to assess beta-adrenergic response.
Main Results:
- In intact myocytes and perforated patch-clamp, colchicine had no effect on shortening, [Ca(2+)](i) transients, or I(Ca,L) under basal or isoproterenol-stimulated conditions.
- In ruptured patch-clamp, colchicine doubled basal I(Ca,L) and abolished the response to isoproterenol.
- Colchicine-treated myocytes showed cell width decrease during ruptured patch-clamp, unlike vehicle-treated cells.
Conclusions:
- Colchicine does not alter calcium signaling or beta-adrenergic response in intact cardiac myocytes.
- Microtubule disruption by colchicine combined with the ruptured patch configuration activates I(Ca,L) and blunts beta-adrenergic response.
- Potential mechanisms include free tubulin loss via dialysis or increased mechanosensitivity due to microtubule disruption, relevant to cardiomyopathies.
