Differential effects of stretch and compression on membrane currents and [Na+]c in ventricular myocytes

Mechano-electrical feedback was studied in the single ventricular myocytes. A small fraction (approximately 10%) of the cell surface could be stretched or compressed by a glass stylus. Stretch depolarised, shortened the action potential and induced extra systoles. Stretch activated non-selective cation currents (I-ns) showed a linear voltage dependence, a reversal potential of 0mV, a pure cation selectivity, and were. blocked by 8 muM Gd3+ or 30 muM streptomycin. Stretch reduced Ca2+ and K+ (I-K) currents. Local compression of broadwise attached cells activated I-K but not I-ns. Cytochalasin D or colchicin, thought to disrupt the cytoskeleton, suppressed the mechanosensitivity of I-ns and I-K. During stretch, the cytosolic sodium concentration increased with spatial heterogeneities, local hotspots with [Na+](c) > 24mM appeared close to surface membrane and t-tubules (pseudoratiometric imaging using Sodium Green fluorescence). Electronprobe microanalysis confirmed this result and indicated that stretch increased total sodium [Na] in cell compartments such as mitochondria, nuclear envelope and nucleus. Our results obtained by local stretch differ from those obtained by end to-end stretch (literature). We speculate that channels may be activated not only by axial but also by shear stress, and, that stretch can activate channels outside the deformed sarcomeres via second messenger. (C) 2003 Elsevier Science Ltd. All rights reserved.