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Microtubule disruption modulates Ca(2+) signaling in rat cardiac myocytes
A M Gómez1, B G Kerfant, G Vassort
1Physiopathologie Cardiovasculaire, INSERM U-390, Montpellier, France.
Abstract:
Microtubules have been shown to alter contraction in cardiac myocytes through changes in cellular stiffness. However, an effect on excitation-contraction coupling has not been examined. Here we analyze the effects of microtubule disruption by 1 micromol/L colchicine on calcium currents (I(Ca)) and [Ca(2+)](i) transients in rat ventricular myocytes. I(Ca) was studied using the whole-cell patch-clamp technique. Colchicine treatment increased I(Ca) density (peak values, -4.6+/-0.4 and -9.1+/-1.3 pA/pF in 11 control and 12 colchicine-treated myocytes, respectively; P<0.05). I(Ca) inactivation was well fitted by a biexponential function. The slow component of inactivation was unchanged, whereas the fast component was accelerated after colchicine treatment (at -10 mV, 11.8+/-1.0 versus 6.7+/-1.0 ms in control versus colchicine-treated cells; P<0.005). [Ca(2+)](i) transients were analyzed by fluo-3 epifluorescence simultaneously with I(Ca). Peak [Ca(2+)](i) transients were significantly increased in cardiac myocytes treated with colchicine. The values of F/F(0) at 0 mV were 1.1+/-0.02 in 9 control cells and 1.4+/-0.1 in 11 colchicine-treated cells (P<0.05). beta-Adrenergic stimulation with 1 micromol/L isoproterenol increased both I(Ca) and [Ca(2+)](i) transient in control cells. However, no significant change was induced by isoproterenol on colchicine-treated cells. Colchicine and isoproterenol effects were similar and not additive. Inhibition of adenylyl cyclase by 200 micromol/L 2'-deoxyadenosine 3'-monophosphate blunted the colchicine effect. We suggest that beta-adrenergic stimulation and microtubule disruption share a common pathway to enhance I(Ca) and [Ca(2+)](i) transient.
Insights
Disrupting microtubules with colchicine enhances calcium currents and calcium transients in rat ventricular myocytes. This effect shares a common pathway with beta-adrenergic stimulation, suggesting a novel regulatory mechanism in cardiac function.
Area of Science:
- Cardiac Electrophysiology
- Cellular Biology
- Microtubule Dynamics
Background:
- Microtubules influence cardiac myocyte contraction via cellular stiffness.
- The impact of microtubules on cardiac excitation-contraction coupling remains largely unexamined.
Purpose of the Study:
- To investigate the effects of microtubule disruption on calcium currents (I(Ca)) and intracellular calcium ([Ca(2+)](i)) transients in rat ventricular myocytes.
- To explore the relationship between microtubule disruption, beta-adrenergic stimulation, and calcium handling in cardiac cells.
Main Methods:
- Whole-cell patch-clamp technique to measure I(Ca) in rat ventricular myocytes.
- Colchicine (1 micromol/L) used to disrupt microtubules.
- Fluo-3 epifluorescence microscopy to simultaneously analyze [Ca(2+)](i) transients.
- Assessment of beta-adrenergic stimulation using isoproterenol (1 micromol/L) and adenylyl cyclase inhibition with 2'-deoxyadenosine 3'-monophosphate (200 micromol/L).
Main Results:
- Colchicine treatment significantly increased I(Ca) density and accelerated the fast component of I(Ca) inactivation.
- Microtubule disruption led to significantly increased peak [Ca(2+)](i) transients.
- Isoproterenol's effects on I(Ca) and [Ca(2+)](i) were mimicked and occluded by colchicine, indicating a shared pathway.
- Inhibition of adenylyl cyclase attenuated the colchicine-induced enhancement of I(Ca) and [Ca(2+)](i) transients.
Conclusions:
- Microtubule disruption enhances calcium currents and intracellular calcium transients in rat ventricular myocytes.
- Both beta-adrenergic stimulation and microtubule disruption appear to converge on a common signaling pathway to modulate cardiac calcium handling.
- These findings reveal a novel role for microtubules in regulating cardiac excitation-contraction coupling.