TRPM4 non-selective cation channel in human atrial fibroblast growth

Cardiac fibroblasts play an important role in cardiac matrix turnover and are involved in cardiac fibrosis development. Ca²⁺ is a driving belt in this phenomenon. This study evaluates the functional expression and contribution of the Ca²⁺-activated channel TRPM4 in atrial fibroblast phenotype. Molecular and electrophysiological investigations were conducted in human atrial fibroblasts in primary culture and in atrial fibroblasts obtained from wild-type and transgenic mice with disrupted Trpm4 gene (Trpm4^-/-). A typical TRPM4 current was recorded on human cells (equal selectivity for Na⁺ and K⁺, activation by internal Ca²⁺, voltage sensitivity, conductance of 23.2 pS, inhibition by 9-phenanthrol (IC₅₀ = 6.1 × 10^-6 mol L^-1)). Its detection rate was 13% on patches at days 2-4 in culture but raised to 100% on patches at day 28. By the same time, a cell growth was observed. This growth was smaller when cells were maintained in the presence of 9-phenanthrol. Similar cell growth was measured on wild-type mice atrial fibroblasts during culture. However, this growth was minimized on Trpm4^-/- mice fibroblasts compared to control animals. In addition, the expression of alpha smooth muscle actin increased during culture of atrial fibroblasts from wild-type mice. This was not observed in Trpm4^-/- mice fibroblasts. It is concluded that TRPM4 participates in fibroblast growth and could thus be involved in cardiac fibrosis.