Impedance components in longitudinal direction in the guinea‐pig taenia coli.

Abstract

When the tissue impedance of the guinea pig taenia coli was measured across a 2 mm sucrose gap in a longitudinal direction, the impedance locus could be fitted by 2 different circular arcs. Their characteristic frequencies were about 0.6 and 240 Hz after 60 min superfusion with sucrose solution. Changing the width of sucrose gap and of transection of tissue and taking the difference between impedances measured at 2 distances showed that the low-frequency locus corresponds to the transverse impedance of the plasma membrane and the high-frequency locus to the longitudinal tissue impedance. A change in the longitudinal tissue impedance was measured during superfusion with sucrose solution, using a frequency range between 5 Hz and 10 kHz. The admittance decreased with time of superfusion and this time course could be expressed by the sum of 3 exponential terms. The fastest component, having a time constant of 1.3 min at 10 kHz, was interpreted to correspond to a process of wash-out extracellular medium. Admittances at zero and infinite frequencies were obtained from the impedance locus. The decrease in these admittances with the time was analyzed and the values at the start of washing were obtained by extrapolating the admittance change to zero time. From these values it was estimated that the myoplasmic resistance was 214 .OMEGA. cm, the junctional resistance 372 .OMEGA. cm, and the junctional capacity 3.1 .mu.F/cm at 25.degree. C. The equivalent circuit of tissue was assumed to be expressed by 2 components in series: 1 for the myoplasmic resistance and the other for the junction with the junctional resistance and capacity in parallel. After 90 min superfusion with sucrose solution, the total tissue impedance measured at zero frequency was increased from 586 to 3034 .OMEGA. cm. In the total impedance the myoplasmic resistance was increased from 214 to 914 .OMEGA. cm and the junctional resistance from 372 to 2120 .OMEGA. cm. The change in junctional resistance was greater than that in myoplasmic resistance during superfusion of sucrose solution.