Abstract
Cardiomyocytes are known to swell in various pathophysiological conditions such as congestive cardiac failure, ischemia, endotoxic shock and dilated or hypertrophic cardiomyopathies. In the present study, we made 3-dimensional imaging of the substrate-attached neonatal rat cardiomyocytes in primary culture using the Scanning Ion Conductance Microscopy (SICM) technique in which a fine-tipped patch pipette is employed as a probe to monitor the cell surface. Hypotonic stimulation caused cell swelling followed by a slow recovery of cell volume (regulatory volume decrease: RVD), which was impaired in the presence of NPPB and phloretin suggesting an involvement of volume-sensitive outwardly rectifying (VSOR) chloride channel therein. Conventional whole-cell recordings revealed large tamoxifen- and phloretin-inhibitable VSOR chloride currents. We next used the same pipette for both imaging the cell by SICM and for patching the specified regions on the cell by a "smart-patch" technique. These on-cell experiments revealed swelling-induced activation of single VSOR channels which exhibit outward rectification, inactivation at large positive potentials and sensitivity to phloretin and tamoxifen. The single VSOR channel activity was found to be evenly distributed over the cell surface membrane of neonatal cardiomyocytes. [Jpn J Physiol 55 Suppl:S75 (2005)]
