SUMMARY1. Intracellular recordings of membrane potential, input resistance and time constant have been made in vitro from the exocrine acinar cells of the mouse pancreas using glass micro-electrodes. The acinar cells were stimulated by acetylcholine (ACh). In some cases ACh was simply directly added to the tissue superfusion bath, in other experiments ACh was applied locally to pancreatic acini by micro-iontophoresis.2. Current-voltage relations were investigated by injecting rectangular de-or hyperpolarizing current pulses through the recording microelectrode. Within a relatively wide range (-20 to -70 9. These results indicate that ACh acts on the acinar cells by increasing the conductance of the plasma membrane to Na and K mainly but possibly 432 ACINAR CELL ELECTROPHYSIOLOGY also to other ions. There is, however, no evidence for an ACh-induced change in membrane Ca conductance. Extracellular Ca appears to control the PNa/PK ratio.

4. In the rabbit pancreas ACh evoked biphasic potential changes: depolarization followed by hyperpolarization. A similar pattern could sometimes also be observed in the mouse pancreas following a brief pulse of ACh addition. In these cases the depolarization was followed by a small but relatively long lasting hyperpolarization. The depolarization was accompanied by a reduction in input resistance.5. Pancreozymin caused depolarization of the acinar cell membrane and a marked reduction in input resistance and time constant.6. In the presence of atropine (1.4 x 106 M) depolarization of the acinar cell membrane by an elevated K concentration (50 mM) in the bathing fluid did not reduce the input resistance.7. It is concluded that the two physiological stimulants of pancreatic protein secretion, ACh and pancreozymin, act on the acinar cells by increasing the permeability of the plasma membrane.

SUMMARY1. 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 hyperpolarizationrs, 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 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 PK: the depolarization frequently preceding the hyperpolarization is probably mainly related to an increase in PNa. The membrane Na-K pump can act electrogenically at least under conditions of Na loading.

SUMMARY1. The intracellular pH (pHi) regulation mechanisms of the outer hair cell (OHC) isolated from the guinea-pig were studied using fluorescence ratio imaging microscopy.2. The OHC pHi in the resting condition was 7-26+O008 (mean+ S.D., n = 49) when the standard solution buffered with HEPES-Tris was superfused.3. Exposure to 25 mM-NH4+ in the absence of HCO3-caused biphasic changes in pH1; a transient increase (7-89 + 0±14, n = 22) followed by a slow decrease (7-57 + 0-12; mean+ S.D.). Removal of external NH4+ by introducing the N-methyl-D-glucamine (NMDG+) solution in the absence of HC03-markedly acidified the pHi to 6-38 +0-12 with little pHi recovery. Subsequent application of the standard Na+ solution restored the pHi to the initial value. The recovery was inhibited by 0.5 mM-amiloride but not by 0-3 mM-DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid).4. In the presence of HC03-, removal of both external NH4+ and Na+ promptly caused an intracellular acidification followed by a pHi recovery. The pHi recovery from an acid load was inhibited by 0-3 mM-DIDS or 10,sM-NPPB (5-nitro-2-(3-phenylpropyl-amino)-benzoate). However, the pHi in the steady state in the presence or absence of HC03-was not altered by addition of 0 5 mM-amiloride or NMDG+ solution. 5. The intracellular buffering power obtained from the NH4+ exposure and withdrawal was -15-1 + 8'7 mm (pH unit)-1 (n = 6) and -14-3 + 5-8 mM (pH unit)-1, respectively. 6. Replacement of external Cl-with gluconate in the HCO3-solution increased the pHi from 7-22 + 0-12 to 7-51 + 0-20 (n = 6), which was inhibited by 0-3 mM-DIDS. Moreover, addition of DIDS to the HCO3-solution increased the pHi by 0*13 + 0X08(n= 8).7. When the external standard solution buffered with HEPES-Tris was replaced with the HCO3-solution, the basal pHi (7-27+0-10) was promptly acidified to 6-87+0-10 then relaxed slowly to 7-00+0-15 (n = 16). 11. The above-mentioned findings indicate that the Na+-H+ and Cl--HCO3-exchangers and HC03-conductive pathway in the cell membrane play a key role in the pHi regulation in OHCs. Also participation of the carbonic anhydrase in the pH1 regulation by facilitating CO2 transfer across the membrane was suggested.

Isolated acinar cells from rat and mouse parotid glands were studied with patch-clamp whole-cell current recordings. Acetylcholine (ACh) stimulation caused a transient inward current at a membrane potential of -70 mV, and a sustained outward current at a membrane potential of 0 mV, in quasi physiological Nat, K+ ion gradients, except the zero-C1-ion gradient condition across the membrane. The reversal potential obtained from the ACh-evoked steady current was about -75 mV, in this ionic condition. When major Cl-ions of both the pipette and the bath solution were replaced, either by glutamate or by sulphate, only a large outward current was observed, at a membrane potential of -60 mV , in the presence of ACh. The addition of Cat+-ionophore A23187 caused responses similar to those evoked by ACh. The reversal potential of A23187-induced current was close to the K+ equilibrium potential of -90 mV, in a C1 -free condition. When K+-free NaCI solution was used in the pipette and the bath, A23187 caused only a large inward current, at a membrane potential of -60 mV. The reversal potential of A23187-evoked current was about -15 mV, in a symmetrical K+-free, NaCI condition. These results suggest that the ACh and A23187 activate Clr as well as K+ conducting pathways via an increase in [Ca2+]i in the parotid acinar cells. The A23187-evoked large K+ current could not be explained solely by a rise in open probability of the channels.