Microtubule proliferation in right ventricular myocytes of rats with monocrotaline-induced pulmonary hypertension

Microtubules are components of the cardiac cytoskeleton that can proliferate in response to pressure-overload in animal and human heart failure. We wished to test whether there was a proliferation of the microtubule cytoskeleton in the right ventricle of rats with pulmonary hypertension induced by monocrotaline (MCT) and whether this contributed to contractile dysfunction. Male Wistar rats were injected with 60 mg/kg of MCT in saline or an equivalent volume of saline (CON). MCT produced clinical signs of heart failure within 4 weeks of injection. Expression of right ventricular mRNA for α-tubulin was measured by real-time reverse transcription polymerase chain reaction. Free and polymerised fractions of β-tubulin protein were assessed using Western blot analysis and immunofluorescence microscopy was used to assess tyrosinated and acetylated (stabilized) microtubules. Right ventricular myocyte contraction was measured in response to the microtubule de-polymeriser colchicine (10 μmol/l for at least 1 h). Compared to CON, in MCT right ventricles there was a small but statistically significant increase in the expression of mRNA for α-tubulin (P < 0.001); total (P < 0.05) and polymerised fraction (P < 0.01) of β-tubulin protein and level of acetylated tubulin (P < 0.01). However colchicine treatment did not increase the contraction of MCT myocytes (P > 0.05) or affect their response to increased stimulation frequency. Our observations support the hypothesis that microtubule proliferation is a common response to pulmonary hypertension in failing right ventricles but suggest that the effect this has on contraction depends upon the specific experimental or clinical conditions that prevail and the subsequent level of microtubule proliferation.