Microtubule Disruption Modulates Ca 2+ Signaling in Rat Cardiac Myocytes

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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 μmol/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 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 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 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 μmol/L 2′-deoxyadenosine 3′-monophosphate blunted the colchicine effect. We suggest that β-adrenergic stimulation and microtubule disruption share a common pathway to enhance I Ca and [Ca 2+ ] i transient.