Rapid Measurement of Isolated Cardiac Muscle Cell Length Using a Line-Scan Camera

A digital imaging technique is described for rapid measurement of the length of isolated cardiac muscle cells. The system uses a 1 ×512-element photodiode array camera interfaced to a digitizer and an LSI 11/73 computer. Orientation of the array with respect to the cell is achieved by an adjustable rectangular mask inserted into the optical path of the microscope phototube. Electrical pulses stimulate the cell and trigger a data acquisition sequence in which output from successive scans is read into a frame store at intervals of approximastely 1 ms for periods of up to 500 ms. Each contraction/relaxation cycle is immediately displayed in slow-scan mode, and the resultant image is transferred to a hard disk via DMA. Subsequent boundary detection is performed using Pascal programs with user-selectable parameters to define threshold and deviation from resting length. Data output is in graphic form and also includes estimates of the characteristics of contraction and relaxation. Examples of data from cells at different temperatures show that the method provides rapid direct measurements of cell length with adequate temporal resolution for investigation of the dynamics of cell shortening.