A synthetic strand of cardiac muscle: its passive electrical properties.

Abstract

A B S T R n O T The passive electrical properties of synthetic strands of cardiac muscle, grown in tissue culture, were studied using two intraeeUular microelectrodes: one to inject a rectangular pulse of current and the other to record the resultant displacement of membrane potential at various distances from the current source. In all preparations, the potential displacement, instead of approaching a steady value as would be expected for a cell with constant electrical properties, increased slowly with time throughout the current step. In such circumstances, the specific electrical constants for the membrane and cytoplasm must not be obtained by applying the usual methods, which are based on the analytical solution of the partial differential equation describing a one-dimensional cell with constant electrical properties. A satisfactory fit of the potential waveforms was, however, obtained with numerical solutions of a modified form of this equation in which the membrane resistance increased linearly with time. Best fits of the waveforms from 12 preparations gave the foUowing values for the membrane resistance times unit length, membrane capacitance per unit length, and for the myoplasmic resistance: 1.22 4-0.13 X 10 ~ f~cm, 0.224 4-0.023 # F . c m -x, and 1.37 -4-0.13 X 107 ~crn -t, respectively. The value of membrane capacitance per unit length was close to that obtained from the time constant of the foot of the action potential and was in keeping with the generally satisfactory fit of the recorded waveforms with solutions of the cable equation in which the membrane impedance is that of a single capacitor and resistor in parallel. The area of membrane per unit length and the cross-sectional area of myoplasm at any given length of the preparation were determined from light and composite electron micrographs, and these were used to calculate the foUowing values for the specific electrical membrane resistance, membrane capacitance, and the resistivity of the cytoplasm: 20.5 + 3.0 )< 103 ftcm z, 1.54 4-0.24 #F.cm-", and 180 -4-34 ~cm, respectively. I N T R O D U C T I O NIn cardiac muscle, as in other excitable cells, the passive electrical properties of the cell m e m b r a n e a n d cytoplasm must be d e t e r m i n e d from observations of

Electrical properties associated with wide intercellular clefts in rabbit Purkinje fibres.

“…Radial non-uniformities in concentration occur more readily because of the disparity in the potassium transport numbers of the cleft membrane and the cleft fluid. In view of the sensitivity of the depletion current measurement, it would be interesting to look for depletion currents in cultured cardiac preparations (Lieberman, Sawanobori, Kootsey & Johnson, 1975, Sachs, 1975 when comparing them to the rabbit Purkinje fibre.…”

Characterization of refractoriness in the sinus node of the rabbit.

“…When premature beats are introduced early in the cardiac cycle, however, there is frequently a depolarization that cannot be measured by this conventional method. We therefore employed a template method that is similar to that described by Jongsma and van Rijn (1972) and Lieberman et al (1975) in their studies of the passive membrane properties of cultured heart cells. The template method is illustrated in Figure 2B.…”

Biology on a Chip: Microfabrication for Studying the Behavior of Cultured Cells

“…Micropatterned cardiomyocyte cultures attempt to recreate this architecture in vitro, and hence may reproduce more faithfully the true physiological conditions of heart muscle and may be also useful for cell-based sensors and tissue engineering applications. Patterning heart cells in culture to create "cable-like" strands was first performed, without microfabrication techniques, by Lieberman and coworkers, who grew dissociated cells in grooves cut in agar 217,218 or used nylon filaments as substrates. 219 Rohr et al 220 found that neonatal rat heart cells prefer to attach to glass over photoresist, so they used photoresist as the non-adherent material.…”