Analysis of tissue amylase output by an automated method

Watching Living Cells in Action in the Exocrine Pancreas: The Palade Prize Lecture

George Palade's pioneering electron microscopical studies of the pancreatic acinar cell revealed the intracellular secretory pathway from the rough endoplasmic reticulum at the base of the cell to the zymogen granules in the apical region. Palade also described for the first time the final stage of exocytotic enzyme secretion into the acinar lumen. The contemporary studies of the mechanism by which secretion is acutely controlled, and how the pancreas is destroyed in the disease acute pancreatitis, rely on monitoring molecular events in the various identified pancreatic cell types in the living pancreas. These studies have been carried out with the help of high-resolution fluorescence recordings, often in conjunction with patch clamp current measurements. In such studies we have gained much detailed information about the regulatory events in the exocrine pancreas in health as well as disease, and new therapeutic opportunities have been revealed.

Challenges and Lessons Learned for Acute Inpatient Rehabilitation of Persons With COVID-19: Clinical Presentation, Assessment, Needs, and Services Utilization

OBJECTIVE

The aim of the study was to present: (1) physiatric care delivery amid the SARS-CoV-2 pandemic, (2) challenges, (3) data from the first cohort of post-COVID-19 inpatient rehabilitation facility patients, and (4) lessons learned by a research consortium of New York and New Jersey rehabilitation institutions.

DESIGN

For this clinical descriptive retrospective study, data were extracted from post-COVID-19 patient records treated at a research consortium of New York and New Jersey rehabilitation inpatient rehabilitation facilities (May 1-June 30, 2020) to characterize admission criteria, physical space, precautions, bed numbers, staffing, employee wellness, leadership, and family communication. For comparison, data from the Uniform Data System and eRehabData databases were analyzed. The research consortium of New York and New Jersey rehabilitation members discussed experiences and lessons learned.

RESULTS

The COVID-19 patients (N = 320) were treated during the study period. Most patients were male, average age of 61.9 yrs, and 40.9% were White. The average acute care length of stay before inpatient rehabilitation facility admission was 24.5 days; mean length of stay at inpatient rehabilitation facilities was 15.2 days. The rehabilitation research consortium of New York and New Jersey rehabilitation institutions reported a greater proportion of COVID-19 patients discharged to home compared with prepandemic data. Some institutions reported higher changes in functional scores during rehabilitation admission, compared with prepandemic data.

CONCLUSIONS

The COVID-19 pandemic acutely affected patient care and overall institutional operations. The research consortium of New York and New Jersey rehabilitation institutions responded dynamically to bed expansions/contractions, staff deployment, and innovations that facilitated safe and effective patient care.

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.

Photodynamic action of rose bengal on isolated rat pancreatic acini: stimulation of amylase release

The halogenated fluorescein derivative, rose bengal, upon photon activation, elicits amylase secretion from isolated, perifused pancreatic acini. This effect is due to production of highly reactive singlet delta oxygen which can permeabilize the cell membrane and may also react chemically with secretagogue receptors, or other functional components of the membrane such as the G-proteins. The profile of photodynamically induced amylase secretion is anion-dependent: it becomes biphasic when the chloride ion is substituted by the glutamate ion, an effect attributed to the action of glutamate on the ionic transport systems of the zymogen granule membrane.

The effects of streptozotocin-induced diabetes on the peptidergic innervation and function of the rat parotid gland

The effects of streptozotocin-induced diabetes on the function and pattern of innervation of the rat parotid gland were investigated. An in vitro preparation was used to measure amylase release and immunohistochemistry was used to examine the innervation of the gland. Basal amylase release and the response to field stimulation were reduced in diabetic animals. In the presence of atropine or a propranolol/phentolamine mixture both control and diabetic responses were attenuated. When all 3 antagonists were present the response to field stimulation (non-adrenergic, non-cholinergic [NANC] response) was about 30% of maximal in untreated rats but virtually abolished in diabetic animals. Substance P (SP), vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY) all stimulated amylase release in untreated rats. However, in diabetic rats the responses to all 3 peptides were reduced. No differences in staining were observed between control and diabetic rats with antisera to tyrosine hydroxylase, substance P. VIP or calcitonin gene-related peptide. In contrast there was a marked reduction in NPY-like immunoreactivity in the acinar tissue of diabetic rats. These data suggest that the diabetic rats had a failure of NANC transmission which appears to be due to a reduced NPY innervation and a lack of responsiveness to peptidergic (SP, VIP and NPY) agonists.

Description of an automated assay for measurement of alpha-amylase in vitro from rat parotid gland slices

1. A modified continuous assay of alpha-amylase is detailed and its usefulness in measuring amylase secretion from rat parotid salivary gland described. 2. The alpha-amylase secretion from the rat parotid gland can be evoked by acetylcholine, substance P and isoprenaline. 3. The secretion of amylase was greatest following isoprenaline stimulation and was of a slower time course than with the other two agonists.

Human pancreatic acinar cells: studies of stimulus-secretion coupling

Elements of stimulus-secretion coupling were studied in human pancreatic acinar cells by using tissue samples obtained from cadaver organ donors. In pancreatic fragments, acetylcholine evoked amylase secretion as well as potassium release and increased the outflux of 45Ca and 86Rb from the prelabeled tissue. In patches of basolateral plasma membrane excised from acinar cell clusters, single-channel potassium currents were recorded. The inside of the plasma membrane faced the bath solution, allowing the effects of changes in the free ionized calcium concentration in contact with the membrane interior to be tested. Two types of calcium-activated potassium-selective channels were found with unit conductances of about 250 and 50 picosiemens (pS), respectively. In both cases channel opening was determined by the electrical potential difference across the plasma membrane and the free ionized calcium concentration in the bath solution. The probability of channel opening was markedly increased by elevation of the free ionized calcium concentration in contact with the membrane inside. The results suggest that the acetylcholine-evoked cellular potassium release occurs via selective membrane potassium channels opened by calcium released intracellularly after the action of the secretagogue.

Phorbol ester (TPA) potentiates noradrenaline and acetylcholine-evoked amylase secretion in the rat pancreas

The effect of the phorbol ester 12-O-tetradeconyl-phorbol-13-acetate (TPA) on noradrenaline (NA) and acetylcholine (ACh)-evoked amylase secretion in isolated segments of rat pancreas was investigated. TPA alone evoked a relatively small increase in amylase output. However, when combined with either noradrenaline or ACh, the phorbol ester markedly enhanced the secretagogue-induced amylase secretion. These effects were dose related. TPA also enhanced the amylase secretion evoked by either the Ca2+ ionophore A23187 or dibutyryl cyclic AMP. This potentiation by TPA of noradrenaline, ACh, Ca2+ ionophore A23187 and dibutyryl cyclic AMP-evoked amylase output may suggest the existence of a third pathway controlling enzyme secretion in the pancreas.

Mechanism of action of insulin on acetylcholine-evoked amylase secretion in the mouse pancreas

The effects of insulin and acetylcholine (ACh) on amylase secretion, transmembrane movement of 45Ca2+ and K+, membrane potential and cyclic nucleotide levels in the isolated mouse pancreas were investigated. Insulin alone had no effect on either amylase secretion or 45Ca2+ fractional efflux but it markedly potentiated the ACh-evoked amylase secretion and significantly reduced the ACh-induced 45Ca2+ fractional efflux. These effects were dose related. Insulin evoked a small membrane hyperpolarization and an increase in K+ efflux. The islet hormone had virtually no effect on ACh-induced membrane depolarization but it markedly enhanced the ACh-elicited K+ efflux. Both insulin and ACh had marked time-dependent effects on the metabolism of adenosine 3',5'-cyclic monophosphate (cyclic AMP). Insulin increased and ACh decreased cyclic AMP concentration when applied separately. However, when added together, insulin and ACh caused a rapid and sustained elevation of cyclic AMP levels. Superfusion of mouse pancreatic fragments with an exogenous lipid-soluble derivative of cyclic AMP (dibutyryl adenosine 3',5'-cyclic monophosphate) caused dose-dependent increases in amylase secretion. Dibutyryl cyclic AMP also markedly enhanced, in a dose-dependent manner, the ACh-evoked amylase secretion. It is concluded that insulin may exert its potentiating action on ACh-evoked amylase output in the mouse pancreatic acinar cells by elevating both cytoplasmic Ca2+ and cyclic AMP levels.

Beta-adrenergic receptor mechanisms in rat parotid glands: activation by nerve stimulation and 3-isobutyl-1-methylxanthine

The technique of electrical field stimulation (e.f.s.) was employed in conjunction with selective pharmacological antagonists to specifically investigate the role of endogenous neurotransmitter(s) in the activation of beta-adrenergic receptor mechanisms in isolated parotid gland segments of the rat. The field-stimulus-induced amylase release due to beta-adrenergic receptor activation was characterized as that persisting in the presence of atropine (10(-5) M) and phentolamine (10(-5) M) and susceptible to blockade by propranolol (5 X 10(-6) M), i.e. combined beta 1- and beta 2-receptor blockade. The selective beta 1-receptor antagonist metoprolol (10(-5) M) was as effective as propranolol in blocking the beta-mediated enzyme release. The selective beta 2-receptor antagonist, H35/25 (10(-5) M) did not significantly affect the field-stimulus-induced amylase release. In the absence of any phosphodiesterase inhibitor the levels of cyclic AMP in the tissues were close to the limit of detection. Field stimulation was however associated with a fourfold increase in cyclic AMP. By comparison isoprenaline (10(-5) M) gave rise to a tenfold increase in cyclic AMP. The changes in cyclic AMP metabolism, in response to both field stimulation and isoprenaline, were greatly enhanced in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). The field-stimulus-induced increase in cyclic AMP was abolished by the beta 1-adrenergic receptor antagonist, metoprolol, but persisted in the presence of the beta 2-adrenergic antagonist, H35/25. IBMX was found to have a potent direct effect on amylase release. IBMX (10(-3) M) also gave rise to a tenfold increase in cyclic AMP. IBMX is then as effective as 10(-5) M-isoprenaline in stimulating both enzyme secretion and cyclic AMP metabolism. The secretory response to IBMX was unaffected by beta-adrenergic blockade by propranolol, was independent of extracellular calcium and did not give rise to 86Rb+ efflux. Importantly, isoprenaline (10(-5) M) failed to evoke any significant increase in amylase release if introduced during sustained superfusion of IBMX, yet it is in such protocols that the greatest changes in cyclic AMP metabolism are seen. The study clearly demonstrates that the beta-adrenergic-receptor-regulated amylase release in response to nerve stimulation is mediated predominantly, if not exclusively, by the beta 1-receptor subtype.(ABSTRACT TRUNCATED AT 400 WORDS)

L-Alanine and L-phenylalanine activate Na+ and K+ conductance pathways in the exocrine mouse pancreas

The effects of some amino acids, L-alanine, L-phenylalanine, DL-alanine, D-alanine and beta-alanine on membrane potential, membrane current, amylase secretion and 45Ca and 86Rb fractional efflux in isolated mouse pancreatic segments were investigated. A two microelectrode voltage clamp technique was applied to study the effects of the amino acids on membrane current. The amino acids evoked dose-dependent (0.05-0.5 mmole) and reversible membrane depolarization and increases in membrane current. The relative potencies of the actions of the amino acids were: L-alanine greater than DL-alanine greater than L-phenylalanine greater than D-alanine greater than beta-alanine. A more detailed study of the action of L-alanine showed that the relationship between the L-alanine-evoked membrane current and membrane potential was virtually linear with reversal of current polarity being observed at a membrane potential of about +30 mV. While the L-alanine-induced increase in membrane conductance was dose-dependent, the reversal potential (EL-ala) was independent of the L-alanine concentration used. Replacement of the normal Na-rich superfusion fluid by a low Na solution (5 mM) markedly reduced the L-alanine-elicited inward current at the normal resting potential. The L-alanine-evoked conductance increase was also reduced in low Na solution and the EL-ala was close to O mV. During the exposure of pancreatic segments to C1 free solution (sulphate substitution) EL-ala was about 12 mV more positive (+ 43.7 +/- 0.8 mV) than during exposure to control solution (+ 31.5 +/- 1.0 mV).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nerve stimulation on enzyme secretion from the in vitro rat pancreas and 3H-release after preincubation with catecholamines

In the presence of the cholinergic antagonist atropine, electrical field stimulation (FS) (5-20 Hz) caused a marked, reversible increase in the amylase output from superfused rat pancreatic segments. Adrenaline and noradrenaline evoked dose-dependent increases in amylase output which were similar to those produced by FS. The FS- and catecholamine-evoked amylase secretions were abolished by the beta-adrenergic antagonist propranolol. The FS-evoked secretion could be abolished by either the removal of external Ca2+ or the application of tetrodotoxin (TTX, 2 X 10(-6) M). FS also resulted in a reversible increase in the fractional efflux of tritium (3H) from rat pancreatic tissues preincubated with either 3H-noradrenaline or 3H-adrenaline. The effects of FS (5-20 Hz) on 3H efflux were abolished by TTX (2 X 10(-6) M). TTX had no effect on the enhancement of 3H efflux caused by elevation of external potassium concentration (high K+, 75 mM). Removal of superfusate Ca2+ completely abolished both the FS- and high K+-induced increases in 3H efflux. These observations suggest that intrinsic nerve stimulation (i.e. FS) results in the Ca2+-dependent release of sympathetic neurotransmitter, noradrenaline, which has a direct secretory action on the rat pancreas. Furthermore, the findings suggest that adrenaline can be taken up by nervous elements. This raises the possibility that uptake and re-release of circulating adrenaline might contribute to the control of rat pancreatic enzyme secretion by the adrenergic nervous system.

Substance P is a functional neurotransmitter in the rat parotid gland

The technique of electrical field stimulation was employed to stimulate the intrinsic nerves of isolated rat parotid gland fragments. Responses to field stimulation were recorded as changes in enzyme secretion (amylase release), radiolabelled ion fluxes (86Rb efflux) and electrophysiological effects (changes in acinar cell membrane potential and input resistance). All effects of field stimulation were abolished by the neurotoxin, tetrodotoxin (TTX). Selective use of pharmacological antagonists revealed that both the sympathetic and parasympathetic nerves to this tissue were being excited by field stimulation. Importantly a significant component of the response to field stimulation persisted in the presence of combined autonomic receptor blockade by atropine, phentolamine and propranolol, i.e. due to release of a non-cholinergic, non-adrenergic neurotransmitter. The non-cholinergic, non-adrenergic neurotransmitter evoked amylase release, 86Rb efflux and electrophysiological effects seen as changes in acinar cell membrane potential and conductance, i.e. stimulus-permeability coupled. Two biologically active peptides, substance P (SP) and vasoactive intestinal polypeptide (VIP) were shown to evoke amylase release in the presence of combined autonomic blockade. VIP however did not evoke any increase in 86Rb efflux, i.e. not stimulus-permeability coupled. All the effects of the non-cholinergic, non-adrenergic transmitter were mimicked by substance P which evokes 86Rb efflux and electrophysiological effects in addition to amylase release. The non-cholinergic, non-adrenergic field stimulus effects on amylase release and 86Rb efflux were abolished or markedly attenuated in tissues which had been desensitized by prior exposure to exogenous substance P. In the presence of VIP, however, the non-cholinergic, non-adrenergic effects persisted and were apparently potentiated. Acute application of the neurotoxin capsaicin first stimulated a transient release of amylase and subsequently abolished the non-cholinergic, non-adrenergic field stimulus-evoked enzyme release. The putative substance P antagonist, D-Pro2, D-Trp7,9 substance P, reversibly blocked the response to both non-cholinergic, non-adrenergic nerve stimulation and exogenous substance P. It was demonstrated however that prolonged exposure to this antagonist is associated with non-reversible and, importantly, non-specific neurotoxic effects. It is concluded that substance P or a closely related peptide is a functional neurotransmitter in the rat parotid gland.

Effects of amino acids, glucagon, insulin and acetylcholine on cyclic nucleotide metabolism and amylase secretion in isolated mouse pancreatic fragments

The effects of amino acids, exogenous islet hormones and acetylcholine on cyclic nucleotide metabolism and amylase secretion in the isolated mouse pancreas have been investigated. The changes in levels of adenosine 3',5'-cyclic monophosphate (cyclic AMP) and guanosine 3',5'-cyclic monophosphate (cyclic GMP) were measured at different times during exposure of pancreatic fragments to amino acids (L-alanine and L-arginine), islet hormones (insulin and glucagon) or acetylcholine (ACh). L-Alanine (1-20 mM) evoked a transient increase in cyclic AMP concentration accompanied by an initial decrease and subsequent increase in the tissue concentration of cyclic GMP. L-Arginine (1-20 mM) induced a complex triphasic change in cyclic AMP concentrations involving an initial rise and a delayed sustained elevation. The changes in levels of cyclic GMP increased only transiently. The effects of insulin (10(-6) M) and to some extent glucagon (5 X 10(-7) M) resembled those seen with L-arginine. The effects of amino acids and islet hormones were all dose-dependent. ACh (10(-7) M) elicited a marked reduction in cyclic AMP concentration and this was accompanied by a concomitant increase in the level of cyclic GMP. The amino acids and the islet hormones had no significant effect on amylase secretion whereas ACh, of course, evoked a large increase in amylase output. The results with the amino acids and islet hormones reveal a clear dissociation between cyclic nucleotide changes and amylase secretion and further suggest that the marked reciprocal changes in cyclic AMP and cyclic GMP concentrations may constitute an important physiological role for the cyclic nucleotides to regulate amino acid transport in the pancreas.

A modified amylase assay, using a fluorescent substrate, and its application to a study of the rat parotid gland in vitro

A modified fluorescence assay for alpha-amylase activity is described. The method employs amylopectin anthranilate as substrate and offers the advantages of economy of time and resources over a previously described technique using the same substrate. The sample containing alpha-amylase is incubated with the substrate for 5 min at 30 degree C in a final volume of 750 microliter. The fluorescent products of the reaction are separated from the substrate by the addition of methanol, and the methanol-soluble fluorescence is measured in a fluorescence spectrometer. A highly reproducible linear relationship between fluorescence and alpha-amylase activity is obtained for enzyme activities up to 2 units. The absolute sensitivity of the assay under these conditions was estimated to be 0.02 EU (= 0.08 EU ml-1). The application of the assay method to a study of the effects of isoprenaline and substance P-like peptides on the release of alpha-amylase from rat parotid gland slices is described. The assay is particularly suitable for studies on agonists, such as substance P, which have a low ceiling effect in terms of amylase release.

Dissociation between stimulant-evoked acinar membrane resistance change and amylase secretion in the mouse parotid gland

1. Isolated segments of mouse parotid gland were superfused with a physiological saline solution. Membrane potential and input resistance were measured with intracellular micro-electrodes. Amylase secretion was monitored using an automated fluorometric assay. The parotid gland was stimulated by exposure to isoprenaline (10(-6)M), ACh (10(-6) M), dibutyryl or monobutyryl cyclic AMP (10(-3)M). 2. ACh evoked a sharp decrease in input resistance (from about 3-6 M omega to 1-2 M omega ) accompanied by a modest (two-fold) increase in amylase output. Both effects were fully reversible. 3. Isoprenaline evoked a marked increase in amylase output (five to ten-fold) reaching maximum after 20-30 min of stimulation. Throughout the period of intensive secretion the input resistance remained at the control level. Short pulses of ACh stimulation dramatically reduced input resistance in this period. 4. Dibutyryl cyclic AMP and monobutyryl cyclic AMP caused marked increases in amylase output (five to ten-fold) peaking 40-50 min after start of the continuous stimulation. This increase in amylase secretion was not accompanied by any change in input resistance. Short pulses of ACh stimulation sharply and reversibly reduced input resistance both in control and test periods. 5. It is concluded that the ACh-evoked reduction in input resistance is not a consequence of the secretory event and that secretion does not itself cause a decrease in input resistance.

Control of enzyme secretion by non-cholinergic, non-adrenergic nerves in guinea pig pancreas

Depolarization of pancreatic cells by exposure to high potassium solutions is associated with release of amylase. In the guinea pig, but not the mouse or cat, this Ca-dependent amylase secretion is resistant to atropine blockade, thus Scheele and Haymovits concluded that the enzyme secretion evoked by K depolarization does not involve release of transmitter from intrapancreatic nerves but is a consequence of Ca uptake into acinar cells mediated by the membrane depolarization. This hypothesis is inconsistent with current concepts of stimulus--secretion coupling in electrically non-excitable cells. The observation of Scheele and Haymovits could, however, also be explained by the release of a non-cholinergic, secretomotor transmitter as a consequence of the depolarization of intrapancreatic nerves. By adapting the technique of electrical field stimulation of isolated pancreatic segments to our studies of amylase secretion, we have now been able to demonstrate both cholinergic and non-cholinergic, non-adrenergic secretomotor nerves in the guinea pig pancreas. Excitation of the non-cholinergic nerves stimulates amylase secretion by a different intracellular coupling mechanism from that activated by cholinergic nerves or by peptides belonging to the cholecystokinin, gastrin or bombesin families.

Continuous automated assay of alpha-amylase release from superfused rat salivary gland

A method of continuous automated amylase assay is described. This relies on the absorption of iodine by starch to produce a blue color that can be quantified colorimetrically. Digestion of the starch by amylase released from parotid tissue slices reduces the intensity of the color formed, allowing quantification of the amylase released. The assay in sensitive to 0.05 U/amylase/ml and linear up to 13 U/ml. Typical tissue responses to acetyl-beta-methylcholine and isoprenaline are presented.

Impaired amylase release from the parotid gland of rats treated with reserpine

Using an automated system for the analysis of amylase, the release of this enzyme was compared in superfused parotid gland segments from control and reserpine treated rats. Stimulant-evoked amylase release was delayed and of smaller magnitude in the glands of the treated animals and a reduction of the transmembrane K+ gradient caused a smaller and short lasting reduction in Ach-evoked release of amylase in the glands from these animals.

In vitro action of bombesin on amylase secretion, membrane potential, and membrane resistance in rat and mouse pancreatic acinar cells. A comparison with other secretagogues

Bombesin caused depolarization of rat or mouse pancreatic acinar cell membrane, reduction of membrane resistance, and a steep rise in amylase output from superfused pancreatic fragments. These effects were similar to those previously described for acetylcholine, cholecystokinin, and gastrin. The dose-response curves for these three effects of bombesin were very similar, with effects being detectable at concentrations of about 30 pM and maximal effects at about 10 nM. The equilibrium potential for the membrane action of bombesin, i.e., the membrane potential at which bombesin did not cause any change in membrane potential, was -16 mV. Similar values for equilibrium potential were obtained with acetylcholine, caerulein and pentagastrin. Bombesin in the higher dose range (10 nM) caused electrical uncoupling of acinar cells within an acinus, i.e., a marked increase in junctional membrane resistance. Similar uncoupling effects were observed after acetylcholine, caerulein, and pentagastrin stimulation. In conclusion, bombesin acts on the pancreatic acinar plasma membrane in exactly the same way as acetylcholine and cholecystokinin-pancreozymin. The electrical uncoupling caused by stimulation is evidence for an increase in cytosol free calcium ion concentration.

The relationship between stimulation-induced potassium release and amylase secretion in the mouse parotid

1. The output of amylase from superfused mouse parotid segments in response to stimulation with acetylcholine (ACh), phenylephrine and isoprenaline during exposure to solutions with varying potassium concentrations was monitored by an on line automated fluorometric method. 2. During stimulation with ACh or phenylephrine a 10-fold increase in superfusion fluid potassium concentration caused an immediate very marked reduction in amylase output which was fully reversible. A 10-fold reduction in potassium concentration resulted in a prominent rise in amylase output. During stimulation with isoprenaline there was no effect on the amylase output of varying the extracellular potassium concentration. Acetylcholine and phenylephrine caused potassium release from the mouse parotid whereas isoprenaline had no such effect. 3. It appears that under conditions where stimulation-induced potassium release is enhanced there is also an enhanced amylase secretion and vice cersa. There may therefore be a link between passive potassium transport and amylase secretion.

Pancreatic acinar cells: the role of calcium in stimulus-secretion coupling

1. Segments of mouse or rat pancreas were placed in a flow cell through which physiological salt solutions of varying composition were pumped at a constant rate. Intracellular recordings of membrane potential, resistance and electrical time constant were made from the acini using fine glass micro-electrodes. In some experiments two micro-electrodes were inserted into two acinar cells within the same acinus to assess directly cell to cell coupling. The concentration of amylase in the effluent was measured continuously. 2. Electrical coupling between two acinar cells was observed when the tips of the two micro-electrodes were less than 50 mum from each other. The coupling ratio was close to 1. Acetylcholine (ACh) always evoked depolarization of exactly the same amplitude in two coupled cells and reduced the amplitude of current-pulse induced membrane potential changes in both cell simultaneously. 3. Stimulation with ACh caused an immediate increase in amylase output. Replacement of superfusion fluid Na by Tris or Cl by sulphate abolished ACh-evoked increase in amylase release, but the subsequent reintroduction of Na or Cl caused an increase in amylase release of a magnitude similar to what was normally observed following stimulation. 4. Omitting Ca from the superfusion fluid and adding EGTA rapidly depolarized the acinar cell membrane, reduced the input resistance and caused a marked reduction in amylase secretion. During exposure to a Ca-free, EGTA containing solution a marked increase in amylase release occurred following maximal ACh stimulation. 5. Addition of small amounts of Mg, Ca or Mn to a Ca-, Mg-free solution caused an increase in membrane potential, input resistance and electrical time constant and markedly increased amylase release. The effect on the electrical parameters was reversed in the absence of extracellular Na while extracellular Na was of no importance for the effect on amylase release. 6. The effect of ACh on amylase was enhanced during superfusion with a fluid containing 20 mM-Ca. The presence of Mn (5 mM) in an otherwise normal control had no effect on ACh-evoked release. 7. These results show that ACh acts on the acinus by reducing the surface cell membrane resistance. It is suggested that the ACh-receptor interaction causes a release of Ca from the surface cell membrane and that the concentration of Ca in the surface cell membrane determines the specific membrane resistance particularly for Na. The release of Ca to the cytosol activates exocytosis while the Na influx is of importance for acinar fluid secretion. The effect of ACh on amylase secretion can be mimicked by agents displacing membrane-bound Ca (Mg, Ca, Mn).

Pancreatic acinar cells: ionic dependence of acetylcholine-induced membrane potential and resistance change

1. 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 micro-electrode. Within a relatively wide range (-20 to -70 mV) there was a linear relation between injected current and change in membrane potential. The slope of such linear curves corresponded to an input resistance of about 3-8 M omega. The membrane time constant was about 5-10 msec. 3. ACh depolarized the cell membrane and caused a marked reduction of input resistance and time constant. The minimum latency of the ACh-induced depolarization (microiontophoretic application) was 100-300 msec. Maximal depolarization was about 20 mV. The effect of this local ACh application was abolished by atropine (1-4 x 10-6 M). The blocking effect of atropine was fully reversible. 4. Stimulating with ACh during the passage of large depolarizing current pulses made it possible simultaneously to observe the effect of ACh at two different levels of resting potential (RP). At the spontaneous RP of about minus 40 mV ACh evoked a depolarization of usual magnitude (15-20 mV) while at the artificially displaced level of about -10 mV a small hyperpolarization (about 5 mV) was observed. It therefore appears that the reversal potential of the transmitter equilibrium potential is about -20 mV. 5. Replacement of the superfusion fluid C1 by sulphate or methylsulphate caused an initial short-lasting depolarization, thereafter the normal resting potential was reassumed...