In the present work, we focus on the longitudinal model of microtubules
(MTs) proposed by Satar i c~̵́ et al. [Phy. Rev. E 48, 89
(1993)], that consider cell MTs to have ferroelectric properties,
i.e., a displacive ferro-distortive system of dimers and usually
referred to as u-model of MTs. It has been shown that during the
hydrolysis of GTP into GDP, the energy released is transferred along the
MTs trough kink-like solitons. Substantially, we propose to
theoretically investigate the dynamic of MTs by intrinsically taking
into account the effect of the oriented molecules of polarized
cytoplasmic water and enzymes surrounding the MT. In this regards, we
introduce a cubic nonlinear term in the electric potential
characterizing the polyelectrolyte features of MTs and show that in
addition to the kink and antikink solitons, asymmetrical bright and dark
solitons, and discrete modes can also propagate along the MTs. Theses
results are supported by numerical analysis. The investigation shows us
that the nonlinear dynamics of MTs is strongly impacted by the intrinsic
electric field, the polyelectrolyte and the viscosity effects. Moreover,
new solitons and discrete solitary modes may help to find new phenomena
occurring in the microtubulin systems.