Differential Modulation of L-type Ca ²⁺ Current by SR Ca ²⁺ Release at the T-Tubules and Surface Membrane of Rat Ventricular Myocytes

We have characterized modulation of ICa by Ca2+ at the t-tubules (ie, in control cells) and surface sarcolemma (ie, in detubulated cells) of cardiac ventricular myocytes, using the whole-cell patch clamp technique to record ICa. ICa inactivation was significantly slower in detubulated cells than in control cells (27.1+/-7.8 ms, n=22, versus 16.4+/-7.9 ms, n=22; P<0.05). In atrial myocytes, which lack t-tubules, ICa inactivation was not changed...