The longitudinal tissue impedance of the smooth muscle of guinea-pig taenia coli.

1. The absolute value of the tissue impedance of the guinea-pig taenia coli was measured in the longitudinal direction in air at 36 degrees C. The relation between the tissue impedance and the separation of the recording electrodes indicated that the tissue has cable-like properties. The frequency dependence of the impedance, observed at various distances from the current supplying electrode, showed that the tissue has a capacity component in the longitudinal direction.2. The tissue impedance in the longitudinal direction was also measured while the tissue was suspended in a narrow tube at 25-28 degrees C. The tissue impedance was calculated on the basis of the difference between the total impedance in Krebs solution and that in Krebs solution containing half the normal Na concentration, knowing the specific resistance of both solutions.3. The impedance per unit volume of the tissue was 370 Omega cm at 10 c/s and 190 Omega cm at 10 kc/s; at these frequencies the impedance was nearly independent of current frequency. The difference between the impedances (370 - 190 = 180 Omega cm) was taken to be the impedance of the junctions between cells. The possibility of slightly lower values for the actual tissue impedance was discussed. The capacity located at or near the junction was calculated to be 1-3 muF/cm, the time constant of the junctional membrane being about 0.5 msec.4. Ca ions (0-12.5 mM) and adrenaline (2 x 10(-7) g/ml.) had no measurable effect on the longitudinal impedance within 10-15 min. In hyperosmotic solution of twice osmolarity (by adding sucrose), the tissue impedance was increased by about 50%. When the tissue was immersed in sucrose solution containing no ions, the impedance gradually increased up to nearly 10 times in the course of 1 hr.