Receptors in Heart Muscle Cells (IMAGE) University of Würzburg Caption Beta1- and beta2-adrenergic receptors in heart muscle cells: In the left cell, beta1 receptors are labeled -- they are found both on the cell surface (yellow) and in the T-tubules (green). In the right cell, the beta2-receptors are labeled -- they appear only in the T-tubules (green), but not on the cell surface (which is therefore not visible in the image). Credit Marc Bathe-Peters & Horst-Holger Boltz Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.