[Dielectric behavior of isolated rat submandibular glands: simulation with a vesicle-inclusion cell model]

In an attempt to correlate the passive electrical properties of the secretory tissue with its structure, I measured AC admittances for isolated rat submandibular glands, over the frequency range between 100 Hz and 500 MHz. Animals were divided into three groups: control and treatment with two different secretagogues, isoproterenol and pilocarpine. Dielectric dispersions observed from control glands had two characteristic frequencies at 2.6 kHz and 59 kHz; the former was of the alpha-type and the latter of the beta-type. Secretagogue-stimulated glands exhibited broader beta-dispersion curves. These dispersion data were analysed on the basis of a "two-shell model" with vesicle inclusions, in which two concentric shells represent the cell membrane and the nuclear envelope, and membrane-bounded vesicles are meant for secretory granules dispersed in the inter-shell space. Simulation by this model generated a good fit to data from the three groups. The analyses revealed that: (i) electric capacities for the cell and granular membranes were 2.1 and 0.9 microF/cm2, respectively; (ii) the conductivity of extracellular matrix was close to that of blood plasma; (iii) the conductivity ratio between cytoplasm and extracellular matrix was approx. 0.4; and (iv) the conductivity ratio between intragranular space and cytoplasm was approx. 0.7.