Membrane potential and resistance measurement in acinar cells from salivary glands in vitro: effect of acetylcholine.

1. Cell membrane potential and input resistance measurements were made on segments of submaxillary glands from mice, rabbits or cats placed in a tissue bath, which was perfused with physiological salt solutions.2. During exposure to a standard Krebs-Henseleit solution, ACh stimulation always evoked a marked decrease in input resistance and time constant. The change in potential evoked by ACh stimulation was either a monophasic hyperpolarization (low resting potential) or a depolarization followed by hyperpolarization (high resting potential).3. Increasing [Ca](o) from 2.56 to 10 mM resulted in an enhanced input resistance. Under this condition it was sometimes possible to obtain current-voltage relations. The relationship was linear in the range -50 to -10 mV. In the absence of extracellular Ca the resting potential was reduced and ACh mostly evoked hyperpolarizations. In those cases when the resting potential remained high biphasic potentials were still observed.4. During exposure to Na-free solutions the resting potential was either unchanged or slightly enhanced. ACh never evoked biphasic potentials, but always large hyperpolarizations.5. In the first period (1 hr) after exposure to a K-free solution ACh normally evoked very large hyperpolarizations, often to more than -100 mV. After several hours of exposure to K-free solution the input resistance gradually increased and ACh evoked a tremendous fall in input resistance and time constant with only a small potential change. Re-introducing control solution, ([K](o) = 4.7) for a short period at this stage, caused a very marked hyperpolarization (about 30 mV) unaccompanied by a change in input resistance and time constant.6. Replacing extracellular Cl by SO(4) hyperpolarized the cell membrane. ACh mostly evoked hyperpolarization under this condition, but occasionally biphasic potentials were observed. Increasing [K] of the sulphate solution depolarized the cell membrane by about 49 mV per tenfold increase in [K]. In the presence of ACh the membrane behaved as a K-selective membrane with a slope of the linear curve relating membrane potential to [K](o) of 59 mV per tenfold increase in [K](o).7. It is concluded that ACh evokes a marked increase in surface cell membrane permeability of salivary acinar cells. The ACh evoked hyperpolarization is due to an increase in P(K): the depolarization frequently preceding the hyperpolarization is probably mainly related to an increase in P(Na). The membrane Na-K pump can act electrogenically at least under conditions of Na loading.