Microtubules mobility affects the modulation of L-type ICa by muscarinic and β-adrenergic agonists in guinea-pig cardiac myocytes

To investigate the interaction of cytoskeleton with the receptor modulation of ionic currents, we studied the effect of muscarinic and β-adrenergic stimulation in adult guinea-pig ventricular cardiac myocytes treated with paclitaxel and colchicine, two drugs that respectively stabilize or destabilize microtubules. We observed that the stabilization of microtubules with paclitaxel (1 μM for 1–4 h) did not markedly affect either the kinetics of ICa, or the stimulatory effect of isoproterenol (Iso, 1 μM); however paclitaxel significantly blunted the response to carbachol (CCh, 1 μM). In agreement with the electrophysiological measurements, Iso induced a similar enhancement of intracellular cAMP levels in both control and paclitaxel-treated cells, while the response to CCh 1 μM was significantly reduced in paclitaxel-treated cells. The reduction of muscarinic response induced by paclitaxel was also evident in atrial cells, in which the stimulation of IKACh by CCh 1 μM was reduced to about 10%. Compared to the muscarinic response, paclitaxel did not have significant effect on the purinergic (adenosine 1–10 μM) modulation of ICa. In contrast to paclitaxel, in colchicine-treated cells, ICa was not enhanced by β-adrenergic stimulation, but instead reduced by CCh, even in the absence of previous stimulation. In conclusion, our data suggest that microtubule stabilization significantly affects the muscarinic modulation of ICa, by interacting with the receptor or the G-protein rather than on the intracellular signaling cascade.