Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC150
Measurement of myocardial sarcoplasmic resistivity by dielectrophoresis and impedance analysis
A. E. Manazza1, S. Salvage1, C. H. Fry1, R. I. Jabr1
1. Division of Clinical Medicine, University of Surrey, Guildford, United Kingdom.
Action potential propagation velocity depends on the intracellular resistance, which in myocardium is the sum of gap junction resistance and the resistivity of the sarcoplasm. The value of sarcoplasmic resistivity has not been routinely measured in mammalian myocardium and thus its overall contribution to intracellular resistance is unclear. We compared two different approaches, dielectrophoresis (the induced motion of particles in non-uniform electric fields) and measurement of cellular impedance to measure sarcoplasmic resistivity, Rs. Experiments used isolated atrial myocytes and strips from guinea pigs, and an immortalised atrial cell line, HL-1 (1). HL-1 cells and freshly isolated atrial myocytes were used for dielectrophoresis and impedance measurements respectively and were suspended in an isotonic solution of Krebs/sucrose to achieve a solution resistivity of about 350 Ω.cm. The analyses to extract cellular electrical constants have been described (2,3). Atrial strips, maintained in an oil-gap chamber, were also used to measure Rs by passing alternating currents along the intracellular pathway (4). Experiments were performed at 25°C and data are means ± SD. Dielectrophoresis yielded a value for Rs of 126±11 Ω.cm, which increased to 271±49 Ω.cm when cells were suspended in sucrose solution omitting divalent cations. Impedance measurements on isolated cell suspensions offered two methods to estimate Rs, from the limiting impedance at high (>60 kHz) and from the frequency at which maximum cellular admittance (1/impedance) was measured: values of 146±42 and 136±59 Ω.cm were obtained respectively. Finally, the impedance of the intracellular pathway was measured and the limiting value at high frequencies (>200 kHz) used, a value of 145±37 Ω.cm was obtained. The values of sarcoplasmic resitivity as measured by four independent physical methods yielded very consistent values, with a mean of 138 Ω.cm, representing a value about 2.5-times that of isosmolar Tyrode’s solution. In atrial tissue this value represents about one-half of the total intracellular resistance (287±94 Ω.cm, unpublished data S Salvage and RI Jabr), the remainder due to gap junction resistance. Thus, Rs itself will significantly influence the value of action potential conduction velocity and as a result substantial changes to gap junction resistance would have to occur before it altered conduction velocity.
Where applicable, experiments conform with Society ethical requirements