Abstract
We have been developing a sarcomere model to account for the physiological Ca release from the junctional sarcoplasmic reticulum (JSR) in the cardiac myocyte based on the Ca-induced Ca-release mechanism of the JSR without any inactivation of the Ca release channel. In the present study, we constructed a cylindrical three-dimensional sarcomere model with the transverse (T)-tublule, the diad, the JSR and the tubular (T)- SR and examined the following problems by simulating the physiological JSR Ca release and a staircase: (1) Where is the Na/Ca exchange localized in the T-tubule? (2) Where does Ca enter into the cytoplasm for replenishing the JSR in diastole? (3) Is Ca uptake activity of the JSR necessary? (4) How fast does Ca move from the T- to the JSR? Simulation was made successfully by assuming (1)(2) the localization of the Na/Ca exchange and the diastolic Ca influx at the diad, (3) a low rate of Ca uptake by the JSR to inhibit the JSR Ca release after the termination of the action potential-dependent Ca influx by lowering the [Ca] in the diadic cleft together with a high rate of Ca uptake by the TSR and (4) slow movement of Ca from the T- to the JSR. We present the [Ca] distribution in the sarcomere at some selected times after the JSR Ca release and the change of the [Ca] with time at some selected points in the sarcomere together with the change of the average [Ca] in the cytoplasm. [Jpn J Physiol 54 Suppl:S120 (2004)]
