Membrane potential measurement in parotid acinar cells

A Mathematical Model Supports a Key Role for Ae4 (Slc4a9) in Salivary Gland Secretion

We develop a mathematical model of a salivary gland acinar cell with the objective of investigating the role of two [Formula: see text] exchangers from the solute carrier family 4 (Slc4), Ae2 (Slc4a2) and Ae4 (Slc4a9), in fluid secretion. Water transport in this type of cell is predominantly driven by [Formula: see text] movement. Here, a basolateral [Formula: see text] adenosine triphosphatase pump (NaK-ATPase) and a [Formula: see text]-[Formula: see text]-[Formula: see text] cotransporter (Nkcc1) are primarily responsible for concentrating the intracellular space with [Formula: see text] well above its equilibrium potential. Gustatory and olfactory stimuli induce the release of [Formula: see text] ions from the internal stores of acinar cells, which triggers saliva secretion. [Formula: see text]-dependent [Formula: see text] and [Formula: see text] channels promote ion secretion into the luminal space, thus creating an osmotic gradient that promotes water movement in the secretory direction. The current model for saliva secretion proposes that [Formula: see text] anion exchangers (Ae), coupled with a basolateral [Formula: see text] ([Formula: see text]) (Nhe1) antiporter, regulate intracellular pH and act as a secondary [Formula: see text] uptake mechanism (Nauntofte in Am J Physiol Gastrointest Liver Physiol 263(6):G823-G837, 1992; Melvin et al. in Annu Rev Physiol 67:445-469, 2005. https://doi.org/10.1146/annurev.physiol.67.041703.084745 ). Recent studies demonstrated that Ae4 deficient mice exhibit an approximate [Formula: see text] decrease in gland salivation (Peña-Münzenmayer et al. in J Biol Chem 290(17):10677-10688, 2015). Surprisingly, the same study revealed that absence of Ae2 does not impair salivation, as previously suggested. These results seem to indicate that the Ae4 may be responsible for the majority of the secondary [Formula: see text] uptake and thus a key mechanism for saliva secretion. Here, by using 'in-silico' Ae2 and Ae4 knockout simulations, we produced mathematical support for such controversial findings. Our results suggest that the exchanger's cotransport of monovalent cations is likely to be important in establishing the osmotic gradient necessary for optimal transepithelial fluid movement.

Ca2+ signalling and Ca2+-activated ion channels in exocrine acinar cells

The development of the calcium signalling field, from its early beginnings some 40 years ago to the present, is described. Calcium signalling in exocrine gland acinar cells and the effects of neurotransmitter- or hormone-elicited rises in the cytosolic calcium ion concentration on ion channel gating are reviewed. The highly polarized arrangement of the organelle systems in living acinar cells is described as well as its importance for the physiologically relevant local and polarized calcium signalling events.

Ionic and pharmacologic characteristics of epithelial cells in a semi-intact preparation of the rat ventral prostate gland

BACKGROUND

The essential ionic and pharmacologic characteristics of epithelial cells within the ducts of the prostate gland are not well known.

METHODS

Experiments were carried out on segments of ventral prostate glands from adult male rats. By using sharp microelectrodes, intracellular epithelial cell and transepithelial (lumen) potentials were recorded in response to ionic substitution and application of ion channel blockers, hormones, and other pharmacologic agents related to prostatic function.

RESULTS

Membrane permeabilities to K(+), Na(+), and Cl(-) were found to account for approximately 43% of the resting membrane potential, whereas some 39% was likely to be metabolic in origin. The membrane potential also responded to adrenaline, acetylcholine, insulin, prolactin, testosterone, nerve growth factor, and nitric oxide. The lumen potential was found to be particularly sensitive to citrate, prolactin, and testosterone.

CONCLUSION

It was concluded that the basal membrane potential of prostatic epithelial cells is associated with a relatively high Na(+):K(+) permeability ratio and metabolic dependence. The hormonal and pharmacologic sensitivity observed is consistent with the functional characteristics of the prostate gland.

Membrane potential modulates divalent cation entry in rat parotid acini

This study examines the effect of membrane potential on divalent cation entry in dispersed parotid acini following stimulation by the muscarinic agonist, carbachol, and during refill of the agonist-sensitive internal Ca2+ pool. Depolarizing conditions (addition of gramicidin to cells in Na(+)-containing medium or incubation of cells in medium with elevated [K+]) prevent carbachol-stimulated hyperpolarization of acini and also inhibit carbachol activation of Ca2+ and Mn2+ entry into these cells. Conditions promoting hyperpolarization (cells in medium with Na+ or with N-methyl-D-glucamine instead of Na+) enhance carbachol stimulation of divalent cation entry. Intracellular Ca2+ release (initial increase in [Ca2+]i) does not appear to be affected by these manipulations. Mn2+ entry into resting and internal Ca2+ pool-depleted cells (10-min carbachol stimulation in a Ca(2+)-free medium) is similarly affected by membrane potential modulations, and refill of the internal pool by Ca2+ is inhibited by depolarization. The inhibitory effects of depolarization on divalent cation entry can be overcome by increasing extracellular [Ca2+] or [Mn2+]. These data demonstrate that the modulation of Ca2+ entry into parotid acini by membrane potential is most likely due to effects on the electrochemical gradient (Em-ECa) for Ca2+ entry.

Action of cholinergic drugs on accumulation of TPMP+ on human spermatozoa

Neurotransmitters or antagonists with nicotinic- or acetylcholine-type receptors were utilized to measure the accumulation of the radiolabeled lipophilic cation triphenylmethylphosphonium (TPMP+) on the plasma membrane of human sperm. Washed sperm incubated in the presence of TPMP+ in a low-K+ or high-K+ medium were allowed to take up the cation to a steady state (i.e., 20 min at 37 degrees C). The difference between TPMP+ in each incubation medium was inserted in the Nernst equation yielding a resting membrane potential of -69 +/- 2 mV. The addition of nicotine or acetylcholine to the low-K+ and high-K+ medium induced a hyperpolarization of 17% and 20%, respectively. In the presence of propranolol the membrane potential decreased by 44%. The association of nicotinic or acetylcholine receptor on human sperm or adrenergic beta-receptor blocking agent may alter the ionic permeability of the membrane, possibly due to hyperpolarization or depolarization.

High K+ elevates cytosolic free Ca concentration due to mobilization from internal storage sites in rat parotid cells

1. Effects of high K+ on cytosolic free Ca concentration ([Ca2+]i) in rat parotid cells were studied using quin2. 2. High K+ elevated [Ca2+]i in a dose-dependent manner in normal and Ca-free media. The elevation of [Ca2+]i induced by high K+ was less in the latter medium. 3. High K+ depolarized the membrane in a dose-dependent manner in normal and Ca-free media. 4. Although monensin increased [Ca2+]i, high K+ did not affect 22Na uptake into cells. 5. After treatment with oligomycin, high K+ but not carbachol raised [Ca2+]i. 6. We suggest that high K+ increases [Ca2+]i due to mobilizing Ca2+ from the intracellular storage site which does not need energy.

Neuroendocrine control of secretion in pancreatic and parotid gland acini and the role of Na+,K+-ATPase activity

The results of our investigations into the localization of Na+,K+-pump activity in pancreatic and parotid acinar cells and the effects of hormones and neurotransmitters on pump turnover can be integrated with data on other aspects of stimulus-response coupling to construct models of the neurohumoral control of protein, fluid, and electrolyte secretion (Fig. 23). In both tissues, Ca2+ and cyclic AMP serve as intracellular messengers. In pancreatic acinar cells, the Ca2+-dependent pathway activated by the occupation of CCK or cholinergic receptors provides the primary stimulus for digestive enzyme secretion. Cyclic AMP plays a comparatively minor role; VIP and secretin are much less effective stimulators of protein secretion. Conversely, cyclic AMP levels in parotid acinar cells, which are modulated primarily through occupation of beta-adrenergic receptors, are a major determinant of enzyme secretion. Activation of the Ca2+-dependent pathway by cholinergic or alpha-adrenergic agonists or substance P is less important. The presence of dual control processes in each gland suggests that the observed differences in effectiveness of cyclic AMP- versus Ca2+-dependent secretagogues may reflect not different mechanisms, but rather a shift in the relative emphasis placed on each pathway. This emphasis could conceivably result from subtle variations in the interaction between cellular protein kinases and phosphatases and their phosphoprotein substrates. Electrolyte secretion, on the other hand, appears to involve both discrete and common entities. In pancreatic acinar cells from rodent species, cholinergic or CCK receptor occupancy elicits a Ca2+-dependent increase in the open-state probability of nonselective cation channels in the basolateral plasma membrane. The resultant influx of Na+ and efflux of K+ is most probably the factor which activates Na+, K+-pumps. Based on electron probe studies of the effects of cholinergic agonists on acinar cell Na+ and K+ contents discussed earlier, a transient reduction in the intracellular K+/Na+ ratio of up to 4-fold may occur. A shift of this magnitude in the cytoplasmic microenvironment of the Na+, K+-pump clearly would have a stimulatory influence (see discussion by Jorgensen, 1980). In addition, Ca2+ itself may have direct effects on Na+,K+-pump activity. Calcium at levels much above 1 microM progressively inhibits Na+,K+-ATPase activity (Tobin et al., 1973; Yingst and Polasek, 1985). In unstimulated guinea pig pancreatic acinar cells, Ca2+i measured by quin-2 fluorescence was 161 +/- 13 nM (Hootman et al., 1985a) which increased to a maximal concentration of 803 +/- 122 nM following CCh stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic-agonist-induced Ca2+ fluxes in rat parotid cells are not Na+-dependent

We investigated the hypothesis that extracellular Na+ is required for the rapid mobilization of Ca2+ by rat parotid cells after adrenergic stimulation. When Na+ salts in the media were osmotically replaced with either choline chloride (+atropine) or sucrose, efflux of 45Ca2+ from preloaded cells, caused by 10 microM-(-)-adrenaline, was unchanged. Similarly adrenaline stimulated 45Ca2+ uptake into cells under nonsteady-state conditions in the presence or absence of Na+. Monensin, a Na+ ionophore, was able to elicit a modest increase in 45Ca2+ efflux, compared with controls. Studies of net 45Ca2+ flux, performed under near-steady-state conditions, showed that adrenaline caused net 45Ca2+ accumulation, whereas monensin caused net 45Ca2+ release. The effect of monensin required the presence of Na+ in the incubation medium. Both 1 mM-LaCl3 and 0.1 mM-D-600 prevented adrenaline-stimulated 45Ca2+ uptake into cells, but had no effect on monensin-induced changes. We conclude that (1) the rapid mobilization of Ca2+ by adrenergic agonists seen in rat parotid cells does not require a Na+out greater than Na+in gradient and (2) the nature of the monensin effect is quite different from the adrenergic-agonist-induced response.

Cell-to-cell communication in cultured Sertoli cells

Junctional transfer of ions in monolayer primary cultures of Sertoli cells has been studied by using conventional techniques. Cells were extensively electrically coupled. Membrane voltage displacements caused by the injected current pulses were measured at variable interelectrode distance. Data analyses were based on a thin-sheet model for current flow (Jongsma and van Rijn, 1972) and yielded a generalized space constant of 248 microns and an internal resistivity of 1.7 kOhm.cm in standard medium. Electrical coupling was inhibited by A23187 Ca2+ ionophore (5 microM).

Ionic mechanisms in secretagogue-induced morphological changes in rat parotid gland

When 10(-5) M carbachol was added to parotid tissue slices incubated in buffer containing Ca++, watery vacuoles were formed in the cells. The percent volume density of vacuoles, as measured from 0.5-micron sections, increased from 0.64 +/- 0.15 SE (n = 7) to 3.09 +/- 0.99 (n = 5) in 10 min and, finally, to 7.27 +/- 1.88 (n = 4) in 30 min. In electron micrographs, most of the vacuoles appeared to arise from a location near the Golgi apparatus. Condensation of nuclear chromatin and a conformational change in mitochondria were also noted immediately after stimulation. The percent volume density values returned to basal levels with the addition of either 5 mM EGTA or 10(-6) M atropine after the addition of carbachol. Nuclei and mitochondria returned to normal configurations. In the presence of either 1 mM ouabain or high K+, or in the absence of added Ca++, carbachol failed to induce vacuole formation. However, low Na+ medium did not prevent the formation of vacuoles due to carbachol. Ultrastructural changes in nuclei and mitochondria were consistently associated with the appearance of vacuoles. Since both high K+ and ouabain blocked vacuole formation, it is unlikely that Na+ or K+ movements were important for the response. Rather, receptor-activated Ca++ influx, which is likely to be inhibited by depolarizing agents (such as high K+ or ouabain), is probably the more important factor in vacuole formation and other concomitant ultrastructural changes.

Voltage and Ca2+-activated K+ channel in baso-lateral acinar cell membranes of mammalian salivary glands

Nervous or hormonal stimulation of many exocrine glands evokes release of cellular K+ (ref. 1), as originally demonstrated in mammalian salivary glands2,3, and is associated with a marked increase in membrane conductance1,4,5. We now demonstrate directly, by using the patch-clamp technique6, the existence of a K+ channel with a large conductance localized in the baso-lateral plasma membranes of mouse and rat salivary gland acinar cells. The K+ channel has a conductance of approximately 250 pS in the presence of high K+ solutions on both sides of the membrane. Although mammalian exocrine glands are believed not to possess voltage-activated channels1,7, the probability of opening the salivary gland K+ channel was increased by membrane depolarization. The frequency of channel opening, particularly at higher membrane potentials, was increased markedly by elevating the internal ionized Ca2+ concentration, as previously shown for high-conductance K+ channels from cells of neural origin8-10. The Ca2+ and voltage-activated K+ channel explains the marked cellular K+ release that is characteristically observed when salivary glands are stimulated to secrete.

Calcium-dependent K+ efflux from rat submandibular gland. The effects of trifluoperazine and quinidine

The Ca2+-dependent K+ efflux from rat submandibular gland was studied using a K+-sensitive electrode. A K+ efflux was induced by either adrenalin or by using the divalent cation ionophore A23187 plus added Ca2+ to bypass the receptor mechanism. Trifluoperazine, which was used to investigate the role of calmodulin, was found to block the adrenalin-induced K+ efflux but not the A23187/Ca2+-induced K+ efflux. The adrenalin-induced K+ efflux was abolished by quinidine and the A23187/Ca2+-induced K+ efflux was significantly reduced by quinidine. In other experiments, the presence of indomethacin did not inhibit the adrenalin-induced K+ efflux, and exogenously added arachidonic acid did not induce a K+ efflux. It is concluded that neither prostaglandin synthesis, nor a cytosolic Ca2+-calmodulin complex is involved in the agonist-induced K+ efflux from rat submandibular gland. A similarity between the Ca2+-dependent K+ efflux mechanism of erythrocyte ghosts and submandibular tissue is indicated by their common response to quinidine.

Parotid acinar cells: ionic dependence of isoprenaline-evoked membrane potential changes

The effect of microionophoretic application of isoprenaline on membrane potential and resistance of mouse parotid acinar cells was investigated. For measurements of membrane resistance and the isoprenaline equilibrium potential (Eiso), two microelectrodes were inserted into neighbouring communicating cells. Passing direct current through one of these electrodes, the resting potential could be set at desired levels and Eiso was determined by plotting the relation between the size of the isoprenaline-evoked potential change and the resting potential. Simple depolarizations were found at relatively high resting potentials, while biphasic potential changes in response to isoprenaline (hyperpolarization followed by depolarization) were observed at low resting potentials. Both depolarizing and hyperpolarizing responses to isoprenaline were accompanied by a reduction of membrane resistance. The isoprenaline equilibrium potential in the initial phase of the response was about -53 mV, but had a value of about -24mV in the delayed phase. The initial isoprenaline-evoked potential change was sensitive to alterations in extracellular Na, K and Cl concentrations. The delayed depolarizing response to isoprenaline was markedly reduced by replacing extracellular Na by Tris or extracellular Cl by SO4. These results indicate that isoprenaline opens up conductance pathways permeable to Na and K.

The effect of herpes virus infection on the membrane potential of parotid acinar cells

Monolayers of feline parotid acinar cells were infected with feline rhinotracheitis herpes virus. Membrane potentials and input resistances were measured before and during infection. Uninfected acinar cells had an average membrane potential of -51 mV and resistances from 6 to 120 mega-ohms; cells infected for more than 18 h had an average membrane potential of -19 mV and resistances from 30 to 100 mega-ohms. The time course of the decrease in membrane potential was studied and was found to commence about ten to 14 h after infection.

Stimulus-response coupling in the human neutrophil. Transmembrane potential and the role of extracellular Na+

Receptor-ligand interactions at the surface of the human neutrophil induce lysosomal enzyme release and the generation of O2.-, responses which are anteceded by changes in the membrane potential (delta psi) as measured by [3H]-triphenylmethylphosphonium ion distribution. Surface stimuli (immune complexes, concanavalin A) initiated a rapid (less than 10 s) hyperpolarization response by both normal and cytochalasin B-treated cells. Replacement of extracellular Na+ with either K+ or choline depressed O2.- generation and lysosomal enzyme release in neutrophils exposed to concanavalin A or immune complexes. Replacement of Na+ with K+ led to a substantial fall in resting membrane potential, whereas replacement of Na+ with choline did not. Thus, depression of O2.- generation and lysosomal enzyme release in Na+-free medium were specifically due to a lack of extracellular Na+ and not to depolarization of the membrane. Although it has been shown that extracellular Na+, and possibly an influx of Na+, is required for optimal neutrophil function, neither depolarization nor Na+ influx per se was sufficient to activate fully these cells, since the Na+ ionophore, monensin, was not an effective stimulus for beta-glucuronidase release or O2.- generation. The hyperpolarization response to neutrophils exposed to immune complexes and to concanavalin A was greatly diminished in both high [K+] and [choline] buffers. Thus, extracellular Na+ was required for an optimal membrane potential response to receptor-ligand interaction. Since O2.- generation and lysosomal enzyme release in response to the Ca2+ ionophore, A23187, were also reduced in the absence of extracellular Na+, it was concluded that extracellular Na+ was also required after induction of Ca2+ fluxes. Ouabain (1 mM) had no effect on O2.- generation, lysosomal enzyme release or the hyperpolarization response to immune complexes, indicating that the hyperpolarization observed on stimulation cannot be due to the action of the electrogenic pump, (Na+ + K+)-ATPase. The experiments indicate that extracellular Na+ is required (1) in the delta psi response triggered by receptor-ligand interaction, and (2) at a step(s) subsequent to Ca2+ fluxes and common to O2.- generation and lysosomal enzyme release.

Electrophysiology of mouse parotid acini: effects of electrical field stimulation and ionophoresis of neurotransmitters

1. Intracellular micro-electrode recordings of membrane potential and input resistance were made from surface acini of mouse parotid glands placed in a Perspex tissue bath through which oxygenated physiological saline solutions were circulated. The acinar cells were stimulated by microionophoresis of both acetylcholine (ACh) and adrenaline (Ad) from extracellular micropipettes, and by electrical field stimulation via a pair of platinum electrodes. 2. The acinar cells had a mean resting membrane potential of -64.9 mV +/- 0.6 S.E. The input resistance of the unstimulated cell was 4.63 M omega +/- 0.19 S.E. In a number of cells spontaneous miniature depolarizations were observed, associated with synchronous reductions in input resistance. 3. The responses to ionophoresis of both ACh and Ad and the response to supra-maximal field stimulation were identical. Stimulation always evoked a marked decrease in input resistance associated with an initial potential change, generally followed by a delayed hyperpolarization during which the input resistance returned to normal. 4. Field-stimulation responses could be evoked to single shock (1-2 msec) and to low frequency (1-4 Hz) stimulation. The latency for this response was 245 msec +/- 12 S.E. 5. The field-stimulation response was shown to be susceptible to blockade of nerve conduction in sodium-free or tetrodotoxin- (TTX-) containing media; and to blockade of neurotransmitter release in calcium-free media. 6. The field-stimulation and ACh responses were recorded at different levels of membrane potential within the same cells by applying either hyperpolarizing or depolarizing direct current through the recording electrode. The membrane potential at which the initial potential change undergoes reversal, i.e. changes from a depolarization to a hyperpolarization, is known as the equilibrium or reversal potential, EFS and EACh respectively. The field-stimulation (FS) and ACh responses underwent simultaneous reversal at about -60 mV, i.e. EFS = EACh. Equilibrium potentials were also determined indirectly by analysis of the responses evoked by each stimulus in the manner described by Trautwein & Dudel (1958). Using this technique the equilibrium potentials of the responses to all three stimuli, field stimulation, ACh and Ad, were again about -60mV, i.e. EFS = EACh = EAd. 7. Both the field-stimulation and ACh responses were abolished by atrophine (10(-6) M) while the response to Ad persisted. Atropine also abolished all spontaneous activity. The alpha-adrenergic blocker phentolamine (10(-5) M) abolished the response to Ad but left the field-stimulation response unaffected. 8. Electrical field stimulation of isolated segments of salivary gland evoked release of endogenous neurotransmitter as a consequence of neural excitation. The technique of field stimulation thus makes it possible to investigate the functional innervation of a gland using the in vitro preparation. In the mouse parotid gland the field stimulus response was mediated by ACh released from parasympathetic nerve endings.

Effect of neural stimulation on acinar cell membrane potentials in isolated pancreas and salivary gland segments

The effect of cholinergic neural excitation by field stimulation on the acinar cell membrane potential was investigated in superfused segments of mouse pancreas and salivary glands (sublingual, submaxillary, and parotid glands). Responses of acinar cells in both exocrine pancreas and salivary glands to the neural excitation obtained by field stimulation were similar to responses previously described in each gland to the externally applied acetylcholine. In the pancreatic acinar cell, electrical field simulation induced depolarization with a latency of 0.3 to 1.2 sec. This depolarization was accompanied by a marked decrease in membrane resistance. The equilibrium potential of the depolarization induced by stimulation was between - 10 and - 20 mV. In the sublingual gland, field stimulation induced depolarization of the acinar cell with a latency of 0.2 to 0.3 sec. The stimulus induced depolarization was block by the addition of atropine. In the submaxillary and parotid glands, field stimulation induced depolarization in some acinar cell and hyperpolarization in other cells. The results support evidence previously presented by Petersen and his colleagues that acetylcholine acts to increase Na+ and K+ or Na+, K+, and Cl- permeabilities in the pancreatic acinar cell and to increase K+ and Na+ permeabilities in the salivary gland [11,24].

Parotid acinar cells: ionic dependence of acetylcholine-evoked membrane potential changes

Segments of mouse parotid were placed in a superfusion chamber. Surface acini were impaled by one or two micro-electrodes for measurement of membrane potential and resistance. The acinus under investigation was stimulated by micro-iontophoretic application of acetylcholine (ACh) or adrenaline. Neighbouring acinar cells were electrically coupled. Electrical coupling between acinar cells only occurred within restricted domains probably corresponding to an acinus or a group of acini. Passing direct current through one intracellular electrode, the resting potential of an acinus could be set at desired levels and the dependency of the ACh-evoked potential change on the resting potential investigated. The ACh null potential (initial effect) was about--60 mV. A delayed hyperpolarizing effect of ACh could not be reversed. The initial ACh-evoked potential change was sensitive to alterations in extracellular Na, K and Cl concentration. The delayed ACh-evoked hyperpolarization was blocked by ouabain, exposure to Na-free or K-free solutions. It is concluded that ACh increases mainly K and Na membrane conductance causing K efflux and Na influx with a subsequent Na activation of an electrogenic Na pump.

Calcium and the control of potassium efflux in the sublingual gland

The effects of cholinergic stimulation on K efflux from rat sublingual gland slices was investigated. The sublingual gland slices appeared stable on incubation as indicated by electrolyte content and ultrastructural analysis. Carbachol induced a biphasic increase in release of 86Rb (an index of K efflux); a transient phase lasting 2--4 min was followed by a sustained (or slowly falling) phase. Both phases of the response were blocked by atropine, but only the sustained phase was blocked by omission of Ca or by the addition of LaCl3. The divalent cationophore A-23187 produced a Ca-dependent release of 86Rb. Substance P stimulated a biphasic release of 86Rb, similar to that obtained with carbachol, but epinephrine did not. The response to substance P demonstrated a Ca dependence similar to that of carbachol. When a transient response to carbachol was elicited, no transient response to carbachol was elicited, no transient response to substance P could be obtained. This suggests that the receptors for these agonists may reside in the same cells. Also, the magnitude of the responses suggests that most of the affected cells are probably the mucous elements of the sublingual gland.

Changes in membrane potential of human granulocytes antecede the metabolic responses to surface stimulation

Human granulocytes (polymorphonuclear leukocytes) exposed to surface stimuli [e.g., immune complexes, concanavalin A (Con A)] generate O(2).(-), undergo a respiratory burst, and secrete lysosomal enzymes. To study the earliest reaction of ligands with surface receptors of granulocytes, purified cells were exposed to bovine serum albumin-anti-albumin complexes (Fc receptors) or Con A (glycoprotein receptors). The membrane potential (DeltaPsi) was measured by distribution of the lipophilic cation [(3)H]triphenylmethyl phosphonium ion. The Nernst equation yielded a resting DeltaPsi of -26.7 mV. Beginning within 10 sec after exposure to the antigen-antibody complex or to Con A, the cells responded with a rapid hyperpolarization --> depolarization --> slow hyperpolarization. Even when phagocytosis was inhibited by cytochalasin B, the triphasic response was obtained: evidence for surface interaction. The hyperpolarization response anteceded O(2).(-) generation (continuous recording) by at least 20-30 sec. O(2).(-) generation in response to immune complexes was stimulated by Ca(2+) whereas DeltaPsi remained unchanged; lack of Ca(2+) in the medium did not inhibit the DeltaPsi response. Dissociation of membrane hyperpolarization from subsequent metabolic responses (O(2).(-) generation) was also found in the presence of steroids (hydrocortisone, methylprednisolone), which inhibited O(2).(-) generation but did not inhibit the DeltaPsi response to antigen-antibody complex. Because O(2).(-) generation could be stimulated (Ca(2+)) or depressed (steroids) without affecting DeltaPsi, the data suggest that DeltaPsi is involved in primary triggering of phagocytic cells and that metabolic stimulation is a secondary consequence of ligand-receptor interactions.

Control of calcium channels by membrane receptors in the rat parotid gland

1. The mechanism of action of agonists that stimulate K release from the parotid gland was investigated by monitoring efflux of 86Rb from rat parotid slices. 2. As in previous studies, the 86Rb release was increased by agonists in a biphasic manner. An early, transient phase occurred that was independent of extracellular Ca. This was followed by a sustained (or slowly falling phase) that required extracellular Ca. 3. The agonists were investigated as to their additivity and to their sensitivity to inhibition by a number of putative Ca-antagonists. 4. When carbachol, epinephrine and Substance P were employed in supramaximal concentrations, no combination of agonists produced a summated 86Rb release response, despite the fact that the Ca concentration was submaximal. 5. The sustained phase of 86Rb release, which is dependent on extracellular Ca, was blocked by La, Ni, Co and neomycin; the transient phase was unaffected by these agents. 6. The local anaesthetics tetracaine and procaine inhibited both the transient and sustained phases of the responses to carbachol and phenylephrine; responses to Substance P and to the divalent cationophore, A23187, were largely refractory to this effect. 7. These results support the contention that, in the parotid, muscarinic, alpha-adrenergic and peptide receptors regulate the same Ca influx sites. 8. Also, these results suggest that La, Ni, Co and neomycin appear to antagonize the action of Ca by impeding inward movement of the cation through activated Ca influx sites. 9. Finally, the local anesthetics appear to inhibit, and therefore, serve to define, a transduction step between receptor occupation and channel activation. 10. In the case of the Substance P mechanism, it appears that the transduction mechanism must be qualitatively different to that for the muscarinic or alpha-adrenergic mechanisms.

Membrane potential and resistance changes induced in salivary gland acinar cells by microiontophoretic application of acetylcholine and adrenergic agonists

The effects of microiontophoretic applications of catecholamines and acetylcholine on parotid acinar cell membrane potential and resistance were investigated using intracellular microelectrode recording in superfused segments of mouse parotid or rat submandibular glands. Short pulses of acetylcholine and alpha-adrenergic agonists had similar effects, consisting of a marked decrease in membrane resistance accompanied by an initial depolization or hyperpolarization depending on the level of the resting membrane potential. This initial response was followed by a slow hyperpolarization occurring at a time when the resistance was increasing towards the prestimulation level. The equilibrium potential for the initial potential change caused by excitation of the cholinergic receptors was investigated directly by setting the membrane potential at different levels by injecting direct current and stimulating the same cell repeatedly with equal doses of acetylcholine. The equilibrium potential was found to be about -55 mV. The delayed hyperpolarization could not be reversed by passing hyperpolarizing current, but actually increased in size with higher membrane potentials. The minimum latency of the effect of acetylcholine or alpha-adrenergic agonists was 200-500 msec. Excitation of beta-adrenoceptors caused, after a long latency of several seconds, a small depolarization. Epinephrine induced a combined alpha- and beta-adrenergic response, with the alpha-component predominating. Blocking the alpha-adrenoceptors with phentolamine revealed the beta-adrenergic depolarization, while blocking the beta-adrenoceptors with propranolol caused the components of the alpha-adrenergic response to become more pronounced. All three receptors (alpha- and beta-adrenoceptors and cholinergic receptors) were present in individual acini.

Membrane potential, resistance, and intercellular communication in the lacrimal gland: effects of acetylcholine and adrenaline

1. Intracellular micro-electrode recordings were made from surface acini of mouse exorbital lacrimal glands placed in a Perspex bath through which oxygenated physiological saline solutions were circulated. Two micro-electrodes were inserted into neighbouring communicating cells. Through one of the electrodes, current pulses could be injected. The cells impaled were stimulated by iontophoresis of acetylcholine (ACh), adrenaline or isoprenaline from an extracellular micropipette. 2. During exposure to standard Krebs solution the resting membrane potential was -42.5 mV +/- 1.2 and the resting input resistance 3.3 Momega +/- 0.3. When the tips of the two intracellular micro-electrodes were more than 100 micrometer apart no electrical coupling between two impaled cells could be detected. At intertip distances below about 80 micrometer coupling was frequently observed. In all such cases the coupling ratio was 1. The resting current-voltage relation was almost linear within the membrane potential range of -30 to -80 mV. 3. During exposure to standard Krebs solution the resting membrane potential was -42.5 mV +/- 1.2 and the resting input resistance 3.3 Momega +/- 0.3. When the tips of the two intracellular micro-electrodes were more than 100 micrometer apart no electrical coupling between two impaled cells could be detected. At intertip distances below about 80 micrometer coupling was frequently observed. In all such cases the coupling ratio was 1. The resting current-voltage relation was almost linear within the membrane potential range of -30 to -80mV. 3. During exposure to standard Krebs solution short iontophoretic pulses of ACh or adrenaline caused fully reversible hyperpolarizations accompanied by marked reduction of surface cell membrane resistance and membrane time constant. The effects of ACh were blocked by atropine (1.4 x 10(-6)M). Iontophoresis of isoprenaline never had any detectable effect on membrane potential or resistance. 4. Applying de- or hyperpolarizing direct currents through one of the two intracellular micro-electrodes the effect of ACh or adrenaline could be observed at different lvels of resting potential. Depolarizing the acinar cell membrane resulted in an enhanced stimulant-evoked hyperpolarization whereas hyperpolarizing the acinar cell membrane resulted in a reduction, and at potentials more negative than -60 mV in a reversal of the stimulant-evoked potential change. The ACh equilibrium potential (EACh) under control conditions was -56.6 mV +/- 1.1 and EAdrenaline was -61.4 mV +/- 1.0. 5. Replacing the control superfusion solution by a Clfree sulphate solution resulted in an immediate shift of EACh towards more negative values. At steady state in the Cl-free solution the resting input resistance was 6.8 Momega +/- 1.3 EACh was -95.9 mV +/- 3.4. 6. Reducing [K]o from the usual 4.7 to 1.0 mM resulted in an immediate marked increase in the amplitude of ACh-evoked hyperpolarization whereas increasing [K]o to 10 mM almost abolished the ACh-evoked potential, but not resistance change. 7...

The effects of temperature and 2,4-dinitrophenol on transmembrane potentials of submandibular acinar cells

1. Micro-electrodes were used to investigate the effect of different temperatures and of DNP on salivary secretory potentials of the cat and the possum produced in response to parasympathetic nerve stimulation. 2. The mean resting potential was unchanged between temperatures of 15 and 40 degrees C in both species. 3. The amplitude of the secretory potential decreased as the temperature was lowered. Below 25 degrees C there was often no response to 1 Hz stimulation but a poorly maintained response to higher frequencies could still be obtained at 20 degrees C. 4. Decrease in temperature prolonged both the latency and time course of the secretory potential. In both species and at all frequencies the latency was increased with a Q10 of about 2-0; the increase in hyperpolarization time had a Q10 of about 1-6. 5. Close arterial injection of DNP (1 times 10- minus 4 M) decreased the amplitude of the parasympathetic secretory potential without affecting its latency and time course or the resting potential. The electrical response to close arterial injection of acetylcholine was also abolished. 6. It was concluded that metabolic energy is required to activate the hyperpolarization mechanism, and this may involve the formation of high-energy phosphate bonds.

Membrane potential and input resistance in acinar cells from cat and rabbit submaxillary glands in vivo: effects of autonomic nerve stimulation

1. Membrane potential and input resistance measurements were made from acinar cells of cat and rabbit submaxillary glands in vivo, using intracellular glass micro-electrodes.2. The mean resting cell membrane potential was higher than previously reported, but ranged widely from -15 to -80 mV.3. Single shock electrical stimulation of the parasympathetic nerve fibres evoked characteristic potential changes. In some cases monophasic hyperpolarizations, in others biphasic responses (depolarization - hyperpolarization) were observed.4. The latency of the hyperpolarizing response was considerably longer (300-550 msec) than the latency of the biphasic response (about 150 msec).5. Hyperpolarizing and biphasic responses could be observed in the same cell at different levels of membrane potential. The initial depolarization of the biphasic response was dependent on the magnitude of the resting potential in such a manner that it was very small or absent at the lowest potentials and increased gradually with increasing level of the resting potential.6. Single-shock stimulation of the sympathetic nerve fibres to the gland did not evoke any response. In the cat, repetitive stimulation evoked hyperpolarizing or biphasic responses similar to those seen after repetitive stimulation of the parasympathetic nerve fibres. In the rabbit small hyperpolarizations were seen in a few cells only; mostly there was no response. Repetitive stimulation of the parasympathetic nerve fibres to the rabbit submaxillary gland evoked complex potential changes mostly of the depolarization-hyperpolarization type.7. Both single shock and repetitive stimulation of the parasympathetic nerve fibres evoked marked reductions in cell input resistance. In the hyperpolarizing cell type the conductance change sometimes preceded the potential change whereas they always occurred simultaneously in the biphasic cell type.8. It is concluded that both the hyperpolarizing and the biphasic secretory potentials are derived from the same type of acinar cells. The neurotransmitter released by the parasympathetic nerve endings (ACh) acts on the acinar cell membrane by increasing the ion permeability.

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.

The effect of glucagon on the liver cell membrane potential

1. Intracellular recordings of membrane potential were made from superficial cells of isolated mouse liver segments superfused with physiological salt solutions.2. The mean resting cell membrane potential was -39.4 mV.3. Glucagon caused a dose-dependent membrane hyperpolarization which was detectable at 10(-9)M and maximal (7 mV) at 10(-7)M. The hyperpolarization started within half a minute after exposure to glucagon. Secretion (2 x 10(-7)M) had no effect on the membrane potential.4. Adrenaline (10(-6)M) and isoprenaline (10(-6)M) also caused membrane hyperpolarization (4-6 mV). The effect of isoprenaline, but not that of adrenaline, was blocked by propranolol (5 x 10(-6)M).5. Dibutyryl adenosine 3',5'-monophosphate (10(-3)M) caused a membrane hyperpolarization of 4-8 mV.6. In the absence of extracellular K or the presence of Strophanthin-G (10(-3)M) the resting potential was decreased and the response to glucagon reduced. During exposure to a solution containing 20 mM-K the resting potential was slightly enhanced and the amplitude of the glucagon-induced hyperpolarization reduced compared with control conditions.7. It is concluded that the effect of glucagon on the membrane potential is due to an interaction with specific membrane receptors probably leading to activation of the membrane-bound adenyl cyclase. It is probable that the hyperpolarization is mediated by cyclic AMP. The hyperpolarization induced by glucagon is dependent on a normal function of the membrane Na-K pump.