The action of dibutyryl adenosine-3':5'-cyclic monophosphoric acid and theophylline on the isolated cat parotid gland.

In the isolated cat parotid gland intraarterially applied dibutyryl cyclic AMP (db-cAMP) (1.0 mM) produced a slow, but often maintained salivary flow. db-cAMP was also able to potentiate secretion evoked by supramaximal doses of intraarterially applied acetylcholine. Similar secretory effects were obtained also after intraarterial application of theophylline (1.0 mM). The secretory responses due to db-cAMP or theophylline were unaccompanied by measurable acinar membrane potential changes and stayed unchanged after cutting the parasympathetic innervation of the gland and after blocking both cholinergic and beta-adrenergic receptors with atropine (10-minus 7 M), and with D-(minus)-N-isopropyl-p-nitrophenol-ethanolamine (INPEA) (10-minus 5 M), respectively. The possibility of the existence of an acinar adenylate cyclase system functionally linked to the beta-adrenergic membrane receptor is discussed.     

Effects of subacute treatment with toluene on cerebrocortical α- and β-adrenergic receptors in the rat. Evidence for an increased number and a reduced affinity of β-adrenergic receptors

Subacute treatment with toluene (80–1500 p.p.m.) produces a dose-dependent reduction of affinity and increase in density of the β-adrenergic antagonist [³H]dihydroalprenolol binding sites in the frontoparietal cortex of the male rat, while the binding characteristics of a,-adrenergic ([³H]WB 4101) and α₂^-adrenergic ([³H]p-aminoclonidine) binding sites in the same region is unaffected by this treatment as evaluated in vitro. Therefore, it is suggested that the cortical β-adrenergic receptors are particularly vulnerable to the action of toluene in vivo. It is speculated that as a result cortical β-adrenergic neurotransmission may be altered following exposure to low concentrations of toluene, possibly related to the physico-chemical properties of toluene, leading to changes in membrane fluidity.     

Vascular and Metabolic Effects of Theophylline,Dibuturyl Cyclic AMP and Dibuturyl Cyclic GMP in Canine Subcutaneous Adipose Tissue in situ1

In canine subcutaneous adipose tissue theophylline (2×10^--⁴ M), cAMP and ATP (10^--⁵ M), and DBcAMP (8×10^--⁴ M) increased blood flow by by approximately 100 per cent. These compounds also antagonized sympathetic vasoconstriction. Theophylline and DBcAMP increased glycerol release dose-dependently, while cAMP and ATP were ineffective up to I mM. Theophylline (0.4–0.8 mM) potentiated the lipolytic effect of nerve stimulation, while 2–8 mM apparently caused maximal stimulation Per se. DBcAMP did not affect FFA release following nerve stimulation, while DBcGMP potentiated. The apparent rate of re-esterification, glucose uptake and lactate release was decreased by theophylline. DBcAMP (0.1–0.4 mM) had no effect on these parameters, while DBcGMP at the same concentration decreased re-esterification and lactate release. Stimulated overflow of ³H from tissues prelabelled with L-³H-noradrenaline was reduced to 50 per cent by ATP (0.1–0.4 mM), but was unaffected by DBcAMP and DBcGMP at the same concentration. The results support the view that cAMP mediates the metabolic actions of sympathetic nerve stimulation in canine subcutaneous adipose tissue. The relationship between cAMP and vascular reactions may be more complex.     

Effects of β-adrenergic agonists in the parotid gland of the rat–an electrophysiological study

The effects of some β-adrenergic agonists were studied in the parotid gland of the rat by electrophysiological techniques. In the unoperated gland, isoprenaline caused depolarizations which were slowly developing, long-lasting and of low amplitude. The same response was seen when noradrenaline was combined with α-adrenoceptor blocking drugs. A greater number of cells responded to this combination than to isoprenaline. After either parasympathetic or sympathetic denervation 1–3 weeks in advance, to induce supersensitivity, the number of cells responding to β-adrenoceptor stimulating drugs was significantly increased. In the latter case the threshold dose required to evoke a response was also significantly lowered. Atropine did not have any effect on the isoprenaline-evoked response. The combined parasympathetic and sympathetic denervation did not further increase the responsiveness. It is concluded that β-adrenoceptor stimulation in the parotid gland of the rat may cause membrane depolarizations. The response is mediated by β₁- adrenoceptors. The responsiveness is increased in the denervated gland. Secretory studies have demonstrated a supersensitivity to β-adrenergic agonists as a result of denervation. On the other hand, β-adrenoceptor stimulation is believed mainly to activate the adenylate cyclase/cyclic AMP system independent of membrane potential changes. It is thus not known if the present ‘supersensitivity’ is correlated to the increased secretory response earlier demonstrated in this gland.     

Control of the Production of Oxygen Intermediates of Human Polymorphonuclear Leukocytes and Monocytes by B-Adrenergic Receptors

Abstract

The control by R-adrenergic receptors of the production of oxygen radicals by zymosan-stimulated human polymorphonuclear leukocytes (PMN) and monocytes (Mψ) was studied in vitro by means of chemiluminescence. In addition we asked whether PMN Mpsi; exhibit differential sensitivity to β-adrenergic stimulation. Eor β-adrenergic stimulation we applied fenoterol ranging from 10^?9 to 10 M × 2.7. We found a dose-dependent suppression of the production of oxygen radicals, the ID50 being approximately 10^?6 M both for PMN and Mpsi;. By assessment of lactic dehydrogenase release a cytotoxic effect of the drug could be ruled out. When incubated together with the β-adrenergic antagonist propranolol at 10^?6 and 10^?7 M the suppressive effect of fenoterol could be reversed in dose-dependency. Preincubation with fenoterol revealed that the inhibitory action on Mpsi; persisted, in contrast, no such suppression could be verified with PMN. Our findings indicate the control of the production of oxygen intermediates of human PMN and Mpsi; by β-adrenergic stimulation. Furthermore, selective functional modulation of resting PMN and Mpsi; by β-adrenoceptors is suggested. These effects may be of importance in vivo, in particular since fenoterol was applied in pharmacological doses.     

Effects of external calcium on acetylcholine-evoked increases in membrane capacitance in rat pancreatic acinar cells

Effects of external calcium on acetylcholine-induced increases in membrane capacitance and conductance were investigated with the patch-clamp technique in combination with the phase-sensitive detection method, in single dialysed pancreatic acinar cells of rats. Both increases depended on an increase in [Ca²⁺]_i, and a high concentration of EGTA in the cell-dialysing solution made ACh ineffective. In acinar cells exposed to a bathing solution containing the normal concentration of Ca²⁺ (2.5 mM CaCl₂), the increase in membrane capacitance was transient and synchronous with that in membrane conductance (current) in response to 0.2 M acetylcholine. However, in a bathing solution without CaCl₂ and with EGTA (0.2 mM), the increase in membrane capacitance was sustained after the membrane conductance recovered to the original level during the ACh-stimulation. The evidence suggests that external calcium facilitates either the resealing of the fusion- or fission-pores formed at the contact between the secretory granule and the luminal cell membrane, or the membrane retrieval (endocytosis) in Ca²⁺-dependent exocytosis.     

Polarized distribution of key membrane transport proteins in the rat submandibular gland

 Immunofluorescence labelling and confocal microscopy were employed to examine the polarized distribution of several membrane transport proteins believed to be essential for salivary secretion in the rat submandibular gland. The Na⁺/K⁺-ATPase, Na⁺/H⁺ exchanger isoform 1 (NHE1), and the secretory Na⁺/K⁺/2Cl^–cotransporter isoform were all found in the basolateral membranes of acinar and intralobular duct cells. Anion exchanger isoform 2 (AE2) was found only in the basolateral membranes of acinar cells, while AE1 was absent from glandular epithelial cells. Aquaporin 5 was detected in the apical membranes of acinar cells, while the cystic fibrosis transmembrane conductance regulator was found only in apical membranes of intralobular duct cells. NHEs 2 and 3 were found in the apical membranes of both acinar and intralobular duct cells. Our results are generally consistent with the expected distribution of most transporters based on previous physiological and pharmacological experiments. However, the apical localization of NHEs 2 and 3, and the presence of the secretory isoform of the Na⁺/K⁺/2Cl^–cotransporter in intralobular duct cells were not predicted. Received: 10 June 1996 / Received after revision: 9 September 1996 / Accepted: 17 September 1996     

β2-Adrenergic stimulation causes detachment of natural killer cells from cultured endothelium

Physical exercise, mental stress, or infusion of β-adrenergic agonists result in an increase in the number of natural killer (NK) cells in the peripheral circulation. In view of the specific migration pattern of NK cells in vivo, it has been suggested that these cells may be released from the marginating pool in blood vessels. In the present report, the in vitro effect of catecholamines on the adhesion of NK cells to unstimulated human endothelial cells (EC) was characterized. Peripheral blood mononuclear cells were allowed to adhere to monolayers of EC, after which the adherent lymphocyte fraction was analyzed phenotypically by flow cytometry. NK cells were found to adhere preferentially to EC, a process that was reversed by the addition of various adrenergic agonists. Catecholamines selectively affected adhesion of NK cells and had no effect on T cell adhesion to EC, as was determined by the use of purified cell populations. Detachment of NK cells from EC could be achieved by short incubations (5 min) with epinephrine (EPI) and was concentration-dependent, with an ED₅₀ of 2 × 10 ^?10M. Using a panel of α and β-adrenergic agonists and antagonists, we show that the detachment of NK cells is mediated via β₂-adrenergic receptors. In line with the lower affinity for β₂-adrenergic receptors, norepinephrine was less effective than EPI in inducing detachment of NK cells from EC. Direct activation of adenylate-cyclase with forskolin gave similar results as observed with EPI, indicating that signaling through cAMP is necessary to induce detachment of NK cells from EC. The results of the present study lend support to the hypothesis that catecholamines, via β₂-adrenergic receptors, can induce recruitment of NK cells from the marginating pool to the circulating pool, by changing the adhesive interactions between NK cells and EC.     

Characterization of granulocyte beta adrenergic receptors in atopic eczema

The binding of (?)-³H-dihydroalprenolol (³H-DHA) and ¹²⁵I-hydroxybenzylpindolol (¹²⁵I-HYP) to the β-adrenergic receptors in homogenized granulocyte preparations from control subjects and patients with atopic eczema was characterized. No difference was found for the affinity (K_D = 2 × 10^?9 M) or the total number of high-affinity binding sites (1,200 to 1,600 per cell) with ³H-DHA or ¹²⁵I-HYP (K_D 1.6 × 10^?10 M) in granulocytes from the two study populations. Scatchard plots of the data obtained from DHA binding isotherms suggested that negative cooperativity may exist as a property of the β₂-receptor. Granulocyte preparations from control subjects and patients with atopic eczema also showed propranolol protectable ³H-DHA binding with a K_D of 10^?7 M. It is not clear whether these ³H-DHA binding sites represent physiologically significant β-adrenergic receptors at these concentrations of radioligand. It was found that 15,000 to 20,000 binding sites of this lower affinity for DHA exist per cell in granulocytes from the two populations of subjects. These data suggest that the reduced isoproterenol responsiveness of granulocytes from patients with atopic eczema is not the result of abnormal or reduced numbers of β-adrenergic receptors.     

Quantitative pharmacological characterization of β-receptors and two types of α-receptors mediating sympathomimetic smooth muscle response in the human Fallopian tube at various cyclic stages

The dissociation constants for adrenoceptor-antagonist complexes (K_B) were determined in vitro in circular and longitudinal smooth musculature from the ampullary and isthmic regions of the human Fallopian tube. High extracellular potassium concentrations were used to eliminate the spontaneous contractile activity. Neuronal and extraneuronal amine uptake mechanisms were blocked. The parallel shift of the log dose-response curves was secured in Arunlakshana-Schild plots. K_B for the β-receptor, mediating sympathomimetic relaxation, were determined during α-receptor blockade: the values for propranolol were the same (approximately 10^--⁶ M) in all preparations and at all cyclic stages, as determined from plasma estradiol and progesterone levels. K_B for the complex between the a-receptor (mediating contraction) and phentolamine were determined during preceptor blockade. The values were the same in all types of smooth musculature, but varied with cyclic stage: they were around 7× 10^--⁸ M when plasma estradiol and progesterone were both minimum, and around 2× 10^--⁷ M when these steroid levels were moderate to high, suggesting that the properties of the contractile receptors of the human Fallopian tube are modified during the menstrual cycle.     

Supersensitivity to substance P and physalaemin in rat salivary glands after denervation or decentralization

Substance P, a putative neurotransmitter in mammals, and physalaemin, present in the skin of an amphibian, are both undecapeptides and belong to the family of tachykinins. The secretory effect of these tachykinins on parotid and submaxillary glands of the rat was examined. Dose-response curves showed that in the unoperated glands maximal secretory responses were obtained to an intravenous dose of 5–10μg/kg of the tachykinins, that the amount of saliva secreted from the submaxillary gland was twice that from the parotid gland, and that physalaemin was more potent than substance P. Parasympathetic denervation of the parotid gland and decentralization of the submaxillary gland caused a marked sensitization to the tachykinins, as judged by lowered threshold doses for secretion and increased secretory responses to a series of submaximal doses 3 weeks postoperatively. Sensitization was less marked after sympathetic denervation and decentralization; in the parotid gland decentralization caused, in fact, no sensitization while in the submaxillary gland the degree of sensitization was about the same after the two types of operation. The tachykinins acted directly on the gland cells and the effect was not exerted via cholinergic, α-adrenergic or β-adrenergic receptors. The pattern of sensitization to the tachykinins, found in the present study, after the different types of operation is similar to that previously found to cholinergic and α-adrenergic agonists and different from that to a β-adrenergic agonist. Studies by others have shown that in the rat parotid gland peptidergic receptors share a common intracellular pathway with cholinergic and α-adrenergic receptors, whereas β-adrenergic receptors use another pathway. In the present study it is suggested that this intracellular arrangement is of importance for the development of supersensitivity.     

Fine structure of the differentiating acini in submandibular glands of isoproterenoltreted rats

Chronic treatment with isoproterenol, a β-adrenergic drug, accelerates the postnatal differentiation of the rat submandibular gland. This report compares the ultrastructure of submandibular glands of acute and chronically treated, 2, 11 and 17-day-old rats with that of controls. In all cases a greater number of acinar cells were found in the treated glands. The correlation noted between changes in the nature of the contents of the condensing vaculoes and Golgi apparatus of some proacinar cells and the formation of secretory granules intermediate in appearance between those of proacinar and acinar cells, support the hypothesis that proacinar cells are the precursors of acinar cells in the young rat. Differences in the morphology of secretory granules in acinar cells of treated and control animals are described. It is concluded that precocious differentiation of the submandibular gland may be induced by the administration of isoproterenol as early as the first day of postnatal life, that proacinar cells become recognized as acinar cells following a change in the nature of their secretory product, and that the secretory material produced by acinar cells in the treated animals is not identical to that of the controls.     

Influences on central hemodynamics in hemorrhage of β2-adrenergic vascular control mechanisms

Central hemodynamic responses evoked by standardized hemorrhage (exsanguination of 20 ml×kg bwt^-1) were followed during 2 h in cats with intact and blocked vascular β₂-adrenoceptors using the ‘selective’β₂-blocker, ICI 118, 551. In the first 10 min after bleeding blood pressure and cardiac output (CO) decreased and total peripheral resistance (TPR) increased by the same amount in the ‘intact’ and β₂-blocked animals. Whereas blood pressure later on reached approximately the same hypotension level in both groups, other hemodynamic variables were distinctly different. In the ‘intact’ animals there was a gradual, partial recovery of stroke volume (SV) and CO in the face of a restoration to control of TPR. In the β₂-blocked animals TPR continued to increase in the face of a maintained low CO and declining SV. The lower SV in the latter group was ascribed to abolition of β₂-adrenergic restoration of plasma volume via absorption of tissue fluid into the circulation. The gradual decline of TPR in the ‘intact’ animals was attributed to β₂-adrenergic dilator interaction with constrictor influences on the resistance vessels. It is concluded that β-adrenergic vascular control mechanisms help to improve nutritional tissue blood flow during hemorrhage by increasing plasma volume, and hence venous return and CO, and by decreasing TPR. These reflex, β₂-adrenergic circulatory events are similar to those aimed at in current shock therapy by transfusion and vasodilator treatment.     

Ca2+-dependent capacitance increases in rat basophilic leukemia cells following activation of store-operated Ca2+ entry and dialysis with high-Ca2+-containing intracellular solution

 Ca²⁺-dependent vesicular fusion was studied in single whole-cell patch-clamped rat basophilic leukemia (RBL) cells using the capacitance technique. Dialysis of the cells with 10 μM free Ca²⁺ and 300 μM guanosine 5′-O-(3-thiotriphosphate) (GTP[γ-S]) resulted in prominent capacitance increases. However, dialysis with either Ca²⁺ (225 nM to 10 μM) or GTP[γ-S] alone failed to induce a capacitance change. Under conditions of weak Ca²⁺ buffering (0.1 mM EGTA), activation of Ca²⁺-release-activated Ca²⁺ (CRAC) channels by dialysis with inositol 1,4,5-trisphosphate (InsP ₃) failed to induce a capacitance increase even in the presence of GTP[γ-S]. However, when Ca²⁺ATPases were inhibited by thapsigargin, InsP ₃ and GTP[γ-S] led to a pronounced elevation in membrane capacitance. This increase was dependent on a rise in intracellular Ca²⁺ because it was abolished when cells were dialysed with a high level of EGTA (10 mM) in the recording pipette. The increase was also dependent on Ca²⁺ influx because it was effectively suppressed when external Ca²⁺ was removed. Our results demonstrate that I _CRAC represents an important source of Ca²⁺ for triggering a secretory response. Received: 1 May 1998 / Received after revision: 15 June 1998 / Accepted: 2 July 1998     

Haemodynamic conditions for renal PGE2 and renin release during α- and β-adrenergic stimulation in dogs

Constriction of the renal artery and infusion of an α-adrenergic agonist induce autoregulated vasodilation and increase prostaglandin E₂ (PGE₂) and renin release. The enhancement of renin release during autoregulated vasodilation might be mediated by prostaglandins. To examine this hypothesis, experiments were performed in three groups of anaesthetized dogs. In six dogs constriction of the renal artery to a perfusion pressure below the range of autoregulation raised renin release from 2 ± 1 to 27 ± 6 μg AI.min^-1 and PGE₂ release from 1 ± 1 to 10 ± 2 pmol. min^-1. After administration of indomethacin (10 mg. kg^-1 b. wt), PGE₂ release was effectively blocked and constriction of the renal artery raised renin release only from 0.1 ± 0.1 to 6 ± 1 μg AI.min^-1. During subsequent continuous infusion of a β-adrenergic agonist, isoproterenol (0.2 μg. kg^-1.min^-1), constriction of the renal artery raised renin release from 0.1 ± 0.1 to 52 ± 11 μg AI.min^-1, although there was no rise in PGE₂ release. In six dogs, intrarenal infusion of phenylephrine, an α adrenergic agonist, increased PGE₂ and renin release before, but not after, indomethacin administration. In six other dogs, phenylephrine infused during isoproterenol infusion increased renin release equally before and after indomethacin administration. Thus the enhancing effect of constricting the renal artery or infusing an α-adrenergic agonist is not dependent upon prostaglandins. We propose that autoregulated dilation enhances renin release whether the stimulatory agent is a prostaglandin or a β-adrenergic agonist.     

Depletion of secretory granules from the feline parotid gland: action of NANC transmitters per se

Ekstrom , J., Asztély , A., Helander , H. F. & Tobin , G. 1994. Depletion of secretory granules from the feline parotid gland: action of NANC transmitters per se. Acta Physiol Scand 150, 83–88. Received 5 May 1993, accepted 30 July 1993. ISSN 0001–6772. Department of Pharmacology, University of Goteborg, and Astra Hassle AB, Molndal, Sweden. A parotid acinar degranulation of approximately 60 and 40% was observed in cats under pentobarbitone anaesthesia after a 90-min period of continuous stimulation of the parasympathetic auriculo-temporal nerve at 10 Hz in the absence and presence of atropine, respectively. Atropine completely abolished the large fluid response of the gland to the nerve stimulation. In the non-atropinized cats, bethanechol, infused into the carotid artery at a dose rate evoking a salivary flow similar to that in response to parasympathetic nerve stimulation, caused an acinar degranulation of approximately 25% and acinar vacuolation. Vasoactive intestinal peptide (VIP; 0.5 μg kg^-1 min^-1 also infused into the carotid artery for 90 min) caused an acinar degranulation of the same magnitude as the parasympathomimetic drug but the peptide did not give rise to any fluid secretion or vacuole formation. The experiments were performed in the presence of α- and β-adrenoceptor blockers. Thus, in parotid glands of the cat, producing no overt secretion of fluid, non-adrenergic, non-cholinergic (NANC) mechanisms may be at work causing exocytosis of the acinar granules. These mechanisms are also likely to contribute to the secretion of granules in response to parasympathetic nerve activity in the absence of blockade of the classical autonomic receptors.     

Increased N-Acetylserotonin and Melatonin Formation Induced by d-Amphetamine in Rat Pineal Gland Organ Culture via a β-Adrenergic Receptor Mechanism

Dextro-amphetamine (10–⁵ M) added to the medium of rat pineal glands in organ culture produces an eightfold increase of radiolabeled N-acetylserotonin and melatonin when tryptophan or serotonin are used as labeled precursors. In concentration of 10–⁴ M d-amphetamine causes a decreased formation of 5-hydroxyindoleacetic acid from tryptophan and serotonin. Addition of d-amphetamine to pineal glands also resulted in an increase of N-acetyltransferase activity as compared with untreated glands. The effect of d-amphetamine and noradrenaline was blocked by propranolol, a β-adrenergic blocking agent but not by the α-adrenergic blocking agent phentolamine. In cervical ganglionectomized rats the addition of d-amphetamine to the culture medium did not produce an increase in N-acetylserotonin production. Conversely noradrenaline added to the medium gave a high formation of N-acetylserotonin. This indicates that the major effects of d-amphetamine on pineal N-acetyl-transferase activity are mediated by noradrenaline.     

Apoptosis induced by β-N-oxalylamino-l-alanine on a motoneuron hybrid cell line

It has been suggested that β-N-oxalylamino-l-alanine, a non-protein amino acid present in the Lathyrus Sativus seeds, may play a role in the etiopathogenesis of neurolathyrism, a toxic form of motor neuron disease clinically characterized by a severe spastic paraparesis. In order to investigate the mechanisms of β-N-oxalylamino-l-alanine-mediated cell death, we studied the effect of this neurotoxin as well as other excitatory amino acids agonists on the growth and survival of motoneuron hybrid ventral spinal cord 4.1 cells. β-N-oxalylamino-l-alanine was toxic to ventral spinal cord 4.1 cells in a concentration-dependent fashion (0.5–10 mM). Among the excitatory amino acids tested, only glutamate (1–10 mM), quisqualate (1 mM) and, with less extent, β-N-methylamino-l-alanine (10 mM) induced a significant reduction of cell survival. The effect of Lathyrus Sativus neurotoxin was a slow process, becoming apparent only after 24–48 h of incubation. Interestingly, a mathematical analysis applied to the time course and dose curve of β-N-oxalylamino-l-alanine toxicity suggested that even for very low concentrations of the amino acid it is theoretically possible to predict a time-dependent effect. The cell death was not blocked by antagonists of N-methyl-d-aspartate or non-N-methyl-d-aspartate receptors; aurintricarboxylic acid and α-tocopherol gave a partial protection; cysteine (1 mM) prevented the toxic effect of both Lathyrus Sativus neurotoxin and glutamate as well as quisqualate. Morphologically, in the presence of either β-N-oxalylamino-l-alanine, glutamate or quisqualate, ventral spinal cord 4.1 cells showed apoptotic features also confirmed by ISEL technique and agarose gel electrophoresis of genomic DNA.Thus, our results suggest that in ventral spinal cord 4.1 motoneuron hybrid cells, in the absence of functional synaptic excitatory amino acid receptors, β-N-oxalylamino-l-alanine induces cell degeneration through an apoptotic mechanism, possibly mediated by a block of cystine/glutamate X⁻_c antiporter.     

Skeletal muscle glycolysis during submaximal exercise following acute β-adrenergic blockade in man

The present study describes the influence of β-adrenergic blockade on glycogen utilization and lactate accumulation in skeletal muscle of exercising man. Twelve physically active men were examined during 25 min of continuous cycle exercise equivalent to 65% of their maximal oxygen uptake both with and without oral administration of 80 mg of propranolol (Inderal®). Heart rate, oxygen uptake, rate of perceived exertion (RPE) and blood lactate concentration were measured during exercise. Muscle biopsies were obtained from m. vastus lateralis after 5 and 25 min of exercise, β-adrenergic blockade decreased steady state exercise heart rate by (mean + SD) 35 ± 10 beats min^-1 (P < 0.001) and oxygen uptake from 2.47 to 2.39 1-min^-1 (P < 0.01). Muscle glycogen decreased from the 5th to the 25th min of exercise, and β-blockade had no significant effect on this decrease. In contrast to without drug, β-blockade resulted in a decrease (P < 0.05) in muscle lactate concentration from the 5th (6.9 mmolkg^-1 w./w.) to the 25th min (4.8 mmolkg^-1 w./w.). Similarly blood lactate levels were lower (P < 0.05) with than without β-blockade in the last but not the first 10 min of exercise. The alteration in muscle lactate concentration pattern following β-blockade, may imply that adrenergic effects per se contribute to the stimulation of glycolysis during submaximal exercise, except in its earliest phase. Nevertheless, the effect is not great enough to produce substantial differences in glycogen utilization.     

Different time courses of GTP[γ-S]-induced exocytosis and current oscillations in isolated mouse pancreatic acinar cells

Exocytosis in isolated mouse pancreatic acinar cells was investigated using the dual-frequency method for measuring membrane capacitance and ionic conductances. Under control conditions, single exo- and endocytotic events could be resolved. The total cell capacitance slightly decreased to 98.7 ± 0.9% of the initial cell capacitance within 10 min after establishing the whole-cell configuration. When guanosine 5′-O-(3-thiophosphate) (GTP[γ-S] was added to the patch pipette, stepwise elevations in membrane capacitance occurred and the cell capacitance increased to 106.7 ± 1.6% within 10 min. Exocytosis was also stimulated by GTP[γ-S] when a Ca²⁺-free pipette solution supplemented with 1 to 10 mM ethylenebis(oxonitrilo) tetraacetate (EGTA) was used. Measurement of the DC current component in parallel with AC current analysis was used to isolate components of the Ca²⁺-dependent Cl⁻ and monovalent cation conductances from the whole-cell conductance. These experiments demonstrate that in GTP[γ-S]-stimulated pancreatic acinar cells: (1) activation of Cl⁻ currents precedes that of cation currents, and (2) fusion of the zymogen granule membrane with the plasma membrane does not lead to incorporation of active Cl⁻ or nonselective cation channels (≥ 10 pS). Received: 11 March 1996/Accepted: 3 May 1996