Excitation-contraction coupling in rat ventricular myocytes after formamide-induced detubulation

Formamide-induced osmotic shock has been used to detubulate isolated adult rat ventricular myocytes (i.e., disrupt the surface membrane-T tubule junct ion). Cell volume, calculated from cell length and width, rapidly decreased and increased upon application and removal of formamide, respectively. Aft er treatment with formamide, membrane capacitance decreased by 26.4% (from 199.4 +/- 18.7 pF in control cells to 146.7 +/- 6.4 pF in formamide-treated cells; n = 1.3, P < 0.05). However, the amplitude of the L-type Ca2+ curre nt (Ic,) decreased by a greater extent (from 0.75 +/- 0.14 to 0.18 +/- 0.03 nA; n = 5, P < 0.05) so that the density of I-Ca decreased by 74.5%. Simul taneous measurements of I-Ca and Ca2+ transients (monitored using fura 2) s howed that both decreased rapidly upon removal of formamide. However, the C a2+ content of the sarcoplasmic reticulum showed little change. Cross-stria tions, visualized with the fluorescent dye di-8-aminonaphthylethenylpyridin ium, were sparse or absent in cells that had been treated with formamide, s uggesting that formamide can successfully detubulate cardiac cells and that I-Ca is concentrated in the T tubules, which therefore play an important r ole in excitation-contraction coupling.