A microwell cell capture device reveals variable response to dobutamine in isolated cardiomyocytes
Isolated ventricular cardiomyocytes exhibit substantial cell-to-cell variability, even when obtained from the same small volume of myocardium. In this study, we investigated the possibility that cardiomyocyte responses to {beta}-adrenergic stimulus are also highly heterogeneous. In order to achieve the throughput and measurement duration desired for these experiments, we designed and validated a novel microwell system that immobilizes and uniformly orients isolated adult cardiomyocytes. In this configuration, detailed drug responses of dozens of cells can be followed in parallel for intervals exceeding one hour. At the conclusion of an experiment, specific cells can also be harvested via a precision aspirator for single-cell gene expression profiling. Using this system, we followed changes in Ca2+ signaling and contractility of individual cells under sustained application of either dobutamine or omecamtiv mecarbil. Both compounds increased average cardiomyocyte contractility over the course of an hour, but responses of individual cells to dobutamine were significantly more variable. Surprisingly, some dobutamine-treated cardiomyocytes augmented Ca2+ release without increasing contractility. Other cells responded with increased contractility in spite of unchanged Ca2+ release. Single-cell gene expression analysis revealed a significant correlation between expression of PRKACA and cellular sensitivity to dobutamine, demonstrating that variable drug responses among cells are not merely experimental artifacts. By enabling direct comparison of the functional behavior of an individual cell and the genes it expresses, this new system constitutes a unique tool for interrogating cardiomyocyte drug responses and discovering the genes that modulate them.\n\nSIGNIFICANCEWe have created a microwell capture device that allows drug responses of dozens of isolated adult cardiomyocytes to be monitored for extended intervals. Using the device, we observed striking diversity in the Ca2+ handling and contractility responses of each cell to a {beta}-adrenergic agonist. This included cells that responded to dobutamine by doubling the amplitude of Ca2+ release while decreasing contractility and vice-versa. We further show that these diverse responses can be linked to gene expression differences between cells. This work demonstrates the feasibility of linking the drug responses of individual cells with their gene expression. It opens the possibility of exploiting cell-to-cell variation to discover new genes that participate in and modulate regulatory cascades.