Breakdown of cytoskeletal filaments selectively reduces Na and Ca spikes in cultured mammal neurones

Abstract

Cytoskeletal filaments, which contain microtubules^1–4 (∼25 nm thick), microfilaments^5,6 (5 nm) and intermediate filaments^7–9 (neurofilaments, 10 nm), are considered essential for maintaining complex cellular shape and various cellular functions. Several studies have claimed that these filaments also maintain in some part physiological properties of excitable membranes^10–14. However, the role of these filaments in maintenance of ionic channel activity is poorly understood^10,11. Here we report experiments in which we disrupted specific cytoskeletal filaments by applying chemicals to tissue-cultured nerve cells of adult guinea pigs^15–17, and examined changes in membrane properties by conventional electrophysiological techniques. Selective breakdown of microfilaments by cytochalasin B^5,6,18–21 or its derivatives^22–24 caused selective reduction in the membrane capacity to carry Na ions¹⁶ (as measured by V_max of pure Na spikes). The ability of the membrane to carry Ca ions¹⁵ and other physiological properties (resting membrane potential, input resistance and capacitance) were not affected significantly. By contrast, a breakdown of microtubules by colchicine^1–4 or vinca alkaloids^4,25 caused selective reduction of V_max for Ca spikes but not of that for Na spikes. These findings suggest that Na channels in the plasma membrane may have a molecular interaction with microfilaments, but are independent of microtubules. Conversely, Ca channels may be related to microtubules or to neurites, but seem to be independent of microfilaments.