AHEART August 46/2

Kawai, Makoto, Munir Hussain, and Clive H. Orchard. Excitation-contraction coupling in rat ventricular myocytes after formamide-induced detubulation. Am. J. Physiol. 277 (Heart Circ. Physiol. 46): H603–H609, 1999.— Formamide-induced osmotic shock has been used to detubulate isolated adult rat ventricular myocytes (i.e., disrupt the surface membrane-T tubule junction). Cell volume, calculated from cell length and width, rapidly decreased and increased upon application and removal of formamide, respectively. After treatment with formamide, membrane capacitance decreased by 26.4% (from 199.4 6 18.7 pF in control cells to 146.7 6 6.4 pF in formamide-treated cells; n 5 13, P , 0.05). However, the amplitude of the L-type Ca21 current (ICa) decreased by a greater extent (from 0.75 6 0.14 to 0.18 6 0.03 nA; n 5 5, P , 0.05) so that the density of ICa decreased by 74.5%. Simultaneous measurements of ICa and Ca21 transients (monitored using fura 2) showed that both decreased rapidly upon removal of formamide. However, the Ca21 content of the sarcoplasmic reticulum showed little change. Cross-striations, visualized with the fluorescent dye di-8aminonaphthylethenylpyridinium, were sparse or absent in cells that had been treated with formamide, suggesting that formamide can successfully detubulate cardiac cells and that ICa is concentrated in the T tubules, which therefore play an important role in excitation-contraction coupling.