A follow-up study on fall and fracture incidence in long-term care including the role of formal caregiver time on fall incidence rates

OBJECTIVE

To examine the impact of a fall prevention programme over a 12 month follow-up period after the introduction of a RCT and to describe possible differences between incidence density rate of falls associated with caregiver time during weekends and ordinary working days.

DESIGN

Prospective observational study, duration 12 months.

SETTING

Six community nursing homes, Germany.

PARTICIPANTS

Long-stay residents (n=881); 771 resident years; median age 85.0 years (min 60; max 101); 79.1% female.

MEASUREMENTS

Incidence density rate of falls and fractures, staff time per resident.

RESULTS

The incidence density rate over all days was 1367/1000 resident years (RY) for falls [95% confidence interval 1041;1693]. The incidence density rate of hip fractures was 29/1000 RY [95% confidence interval 12;45] and 29/1000 RY [95% confidence interval 12;45] for non-hip fractures. The incidence density rate showed similar results comparing weekends/ public holidays vs normal working days; falls 1193 vs 1447/ 1000 RY; hip fractures 25 vs 30/ 1000 RY and other fractures 16 vs 34/1000 RY.

CONCLUSION

During the period, we observed a marked decline of the fracture rate compared with the controlled phase of the intervention trial. A lower number of nursing care hours on weekends was not associated with a higher incidence density rate for falls, fallers, or any type of fracture.

Medizin im Altenheim—

The introduction of the German mandatory long-term care insurance in 1995 has led to major changes in the delivery of medical services in nursing homes. This is a result of the assessment process, the demographic changes, modified access to facilities and the changing socioeconomic resources of informal caregivers. The fusion of the health care and long-term care insurance system is now being proposed by bipartisan committees. This will lead to major changes as well as the immediate announced changes of the long-term care insurance. The article gives an overview of these recent developments based on expert opinion.

[Minimal Change Glomerulonephritis]

We report two cases of minimal change glomerulonephritis (synonyms: idiopathic nephrotic syndrom, minimal change disease). A 47-year old female patient was admitted to our unit with a relapsing nephrotic syndrome since childhood. Another patient, a 22-year old female, presented with moderately swollen legs that developed over several months and a complaint of frequent upper respiratory tract infections during the last year. In both cases we suspected a minimal change glomerulonephritis which can only be proven by renal biopsy. Therapeutic options comprise steroids, cyclosporin, tacrolimus or even cyclophosphamide, depending on the clinical presentation of the disease in the individual case.

[Abilities and restrictions of nursing home residents. Evaluation with the Minimum Data Set of the Resident Assessment Instrument]

The main objective of the study was to examine the prevalence of problems and resources of an unselected cohort of nursing home residents. The sample includes residents (n=769) of an urban area in Southern Germany. The assessment definitions were used according to the Minimum Data Set of the Resident Assessment Instruments (Version 2.0).

RESULTS

The mean age was 84.2 years, 608 of the residents were female. Dementia (446) and stroke (185) were the most common main diagnosis. Syndrome prevalences are reported for depressive symptoms (323), mobility impairments (608), urinary incontinence (461), decubitus (54), use of restraints (54), disruptive behavior (185), psychopharmacy (377), severe visual impairment (123) and severe hearing impairment (123).

Hans Ussing, experiments and models

The article describes work and impact of Hans H. Ussing, a founder of epithelial physiology. Emphasis is on Ussing's model of epithelial transport, which showed early how a complex function can arise from a few basic principles. The KJU-model was developed 1958 for the amphibian epidermis and later applied and adapted to many epithelia, but especially to those that express amiloride-sensitive sodium channels in their apical membrane. Some of the subsequent research dealing with such channels and their cellular environment is briefly reviewed. The ideas of Hans Ussing were and are an inspiration to many of us, who continue to work in the way Ussing has taught us.

Anticancer effect of a lentiviral vector capable of expressing HIV-1 Vpr

A lentiviral vector capable of expressing the HIV-1 vpr gene (Vpr lentiviral vector) was constructed, and its in vivo anticancer effect was determined against cutaneous tumors derived from the AT-84 oral cancer cells in immunocompetent mice. A single intratumoral injection of the Vpr lentiviral vector not only significantly reduced the primary tumor volume but also completely regressed tumors in >40% of animals. More interestingly, the mice of which the primary tumors were completely regressed by the Vpr lentiviral vector were additionally protected from a secondary challenge of AT-84 cells. These data suggest that the Vpr lentiviral vector elicits its anticancer activity in part by the activation of the immune system. The above suggestion is additionally supported by the failure of the lentiviral vector to demonstrate anticancer activity in immunocompromised nude or SCID mice. The Vpr lentiviral vector offers a powerful new strategy for cancer gene therapy and may be useful for the control of solid tumors, such as human oral squamous cell carcinomas.

Hyperpolarization-activated channels HCN1 and HCN4 mediate responses to sour stimuli

Sour taste is initiated by protons acting at receptor proteins or channels. In vertebrates, transduction of this taste quality involves several parallel pathways. Here we examine the effects of sour stimuli on taste cells in slices of vallate papilla from rat. From a subset of cells, we identified a hyperpolarization-activated current that was enhanced by sour stimulation at the taste pore. This current resembled Ih found in neurons and cardio-myocytes, a current carried by members of the family of hyperpolarization-activated and cyclic-nucleotide-gated (HCN) channels. We show by in situ hybridization and immunohistochemistry that HCN1 and HCN4 are expressed in a subset of taste cells. By contrast, gustducin, the G-protein involved in bitter and sweet taste, is not expressed in these cells. Lowering extracellular pH causes a dose-dependent flattening of the activation curve of HCN channels and a shift in the voltage of half-maximal activation to more positive voltages. Our results indicate that HCN channels are gated by extracellular protons and may act as receptors for sour taste.

Receptors and transduction in taste

Taste is the sensory system devoted primarily to a quality check of food to be ingested. Although aided by smell and visual inspection, the final recognition and selection relies on chemoreceptive events in the mouth. Emotional states of acute pleasure or displeasure guide the selection and contribute much to our quality of life. Membrane proteins that serve as receptors for the transduction of taste have for a long time remained elusive. But screening the mass of genome sequence data that have recently become available has provided a new means to identify key receptors for bitter and sweet taste. Molecular biology has also identified receptors for salty, sour and umami taste.

Noninvasive measurement of chloride concentration in rat olfactory receptor cells with use of a fluorescent dye

Inwardly directed Ca(2+)-dependent chloride currents are thought to prolong and boost the odorant-induced transient receptor currents in olfactory cilia. Cl(-) inward current, of course, requires a sufficiently high intracellular Cl(-) concentration ([Cl(-)](i)). In previous measurements using a fluorescent Cl(-) probe, N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE), [Cl(-)](i) of newt olfactory cells was estimated to be only 40 mM. This low value led us to reexamine the [Cl(-)](i) by an improved procedure. When isolated rat olfactory neurons were bathed in Tyrode's solution (150 mM Cl(-)) at room temperature, the [Cl(-)] was 81.5 +/- 13.5 mM (mean +/- SE) in the tip of the dendrite (olfactory knob) and 81.8 +/- 10.2 mM (mean +/- SE) in the soma. The corresponding Cl(-) equilibrium potentials were -15.4 and -15.3 mV, respectively. Therefore, at resting potentials in the range of -90 to -50 mV, Cl(-) currents are predicted to be inward and capable of contributing to the depolarization induced by odorants. Yet, if the cell was depolarized beyond -15 mV, somal Cl(-) currents would be outward and facilitate repolarization during excitation. The measured [Cl(-)] in soma and knob are of interest, because in the cilia the chloride content may be expected to equilibrate with that of the knob in the resting state. They provide a starting point for the decrease in ciliary [Cl(-)] predicted to occur during transduction.

Predicted profiles of ion concentrations in olfactory cilia in the steady state

The role of ciliary geometry for transduction events was explored by numerical simulation. The changes in intraciliary ion concentrations, suspected to occur during transduction, could thus be estimated. The case of a single excised cilium, having a uniform distribution of membrane channels, voltage clamped to -80 mV, was especially investigated. The axial profile of membrane voltage was that of a leaky cable. The Ca(2+) concentration profile tended to show a maximum in proximal segments, due to a preponderance of Ca(2+) inflow over Ca(2+) export at those locations. The local increase in Ca(2+) concentration activated Cl(-) channels. The resulting current caused a local drop in Cl(-) concentration, especially at the tip of the cilium and in distal segments, accompanied by a drop in ciliary K(+) concentration. In consequence, the membrane Cl(-) current was low in distal segments but stronger in proximal segments, where resupply was sufficient. The model predicts that the Cl(-) depletion will codetermine the time course of the receptor potential or current and the ciliary stimulus-response curve. In conclusion, when modeling with transduction elements presently known to participate, the ciliary geometry has large effects on ion distributions and transduction currents because ciliary ion transport is limited by axial electrodiffusion.

Localization of the glutamate-aspartate transporter, GLAST, in rat taste buds

A number of putative neurotransmitter substances have been found in vertebrate taste buds. Amongst these glutamate has been localized in fibres innervating the buds and uptake of glutamate has been shown to occur into receptor cells. It is therefore possible that, in common with other sensory systems, glutamate is a neurotransmitter in taste buds. In the inner ear and retina of mammals, the membranes of supporting cells have been shown to contain the glial glutamate transporter GLAST. In the brain, this protein is involved in glutamate re-uptake into glial cells where the glutamate is converted into glutamine for recycling into glutamatergic terminals. In this study, the presence of GLAST has been investigated in taste buds in the rat vallate papilla and its distribution compared with that of glutamine to determine whether there are cells in this system that play a glia-like role in glutamate handling. Immunofluorescent labelling showed that a subset of cells in the taste bud contains GLAST. Immunogold labelling indicated that it occurs in the plasma membranes of supporting cells, especially on the fine cytoplasmic processes of dark cells towards the basal region of the bud. A protein of molecular mass similar to that of cerebellar GLAST was detected in immunoblots of excised papillae. Double labelling and semiquantitative analysis of glutamine and GLAST immunoreactivity showed that the GLAST-positive cells have a higher level of cytoplasmic glutamine than the adjacent cells. It is proposed that these GLAST-positive cells play a glia-like role in the uptake of glutamate following its release at synapses within the taste bud although the precise location of the latter remains uncertain. The GLAST-positive cells may also be involved in its subsequent conversion to glutamine in a glutamate/glutamine cycle similar to that described in the brain.

Differential expression of RNA and protein of the three pore-forming subunits of the amiloride-sensitive epithelial sodium channel in taste buds of the rat

Salt taste signals from the rat anterior tongue are probably transduced via epithelial sodium channels (ENaCs) residing in the apical cellular pole of taste cells. The signals are blocked by mucosal amiloride in low microM concentrations. In contrast, the rat vallate papilla does not contribute to amiloride-blockable salt taste. Two approaches were used to probe for the three subunits of ENaC in the anterior and posterior tongue of the rats in sodium balance. (a) Immunohistochemistry with antibodies against ENaC subunits and against amiloride binding sites. In the anterior tongue, reactivity for alpha-, beta-, and gamma-subunits was present in taste buds and lingual epithelium. In the posterior tongue vallate papilla, reactivity for alpha-subunit and for amiloride binding sites was easily demonstrable, whereas that for beta-subunit and especially for gamma-subunit was weaker than in the anterior tongue. (b) RT-PCR techniques were used to probe for the presence of ENaC subunit mRNA. In isolated taste buds of the anterior tongue, mRNA of all three subunits was found, whereas in isolated taste buds of the vallate papilla only mRNA of the alpha-subunit was easily detectable. That of beta- and gamma-subunits was much less abundant. RNA of all three subunits was abundant only in taste buds of the anterior tongue. Therefore, subsets of elongated taste cells do express ENaC, but regional differences exist in the transcription and expression of subunits. The regional differences suggest that amiloride-sensitive salt taste, which requires all three subunits, is present in the anterior but not the posterior tongue of rats, as functional studies indicate.

Ultrastructure of taste receptor cells in active and hibernating ground squirrels

Differences in taste bud ultrastructure between active and low-temperature hibernation states were investigated in the Siberian ground squirrel, Citellus undulatus. Compared to active summer animals, taste bud volume and the morphology of the taste pore showed little change while an animal was hibernating. However, impressive differences were observed in nuclei and cytoplasmic organelles of all cells within taste buds. In low-temperature hibernation the nucleoli of elongated, non-dark cells had few, but large, fibrillar centres, a sign of inactivity. In the cytoplasm, the number of free polyribosomes (polysomes) was sharply decreased; ribosomes were seen mainly as (non-synthesizing) monosomes and more seldom as membrane-associated ribosomes. Profiles of endoplasmic reticulum (ER) were reduced, to the extent that only separate and rare cisternae of smooth and rough ER remained. The large vacuoles, which are typically found in many taste cells of active animals, were absent during hibernation, and the Golgi apparatus appeared to be disassembled into numerous vesicles. Of these, many had small diameters near 60 nm, while a few had larger diameters near 300 nm. Secretory organelles (dense granules in dark cells and dense-cored vesicles in type III cells) were rare during hibernation, the lateral plasma membrane was smooth, and signs of exocytosis were not found. These changes suggest reduced protein synthesis and reduced sensory function during hibernation.

Occurrence of ENaC subunit mRNA and immunocytochemistry of the channel subunits in taste buds of the rat vallate papilla

Epithelial Na+ channels (ENaCs) are thought to mediate the amiloride-blockable salt taste. The rat vallate papilla does not contribute to amiloride-blockable salt taste, yet the presence of ENaC-mRNA in this tissue has been reported. Is ENaC actually contained in the taste cells, or is it merely present in the supporting lingual epithelium? To avoid contamination by ENaC contained in the lingual epithelium, we physically isolated taste buds from the vallate papilla and used mRNA purification followed by reverse transcriptase polymerase chain reaction (RT-PCR) to investigate the presence of ENaC-type message in the isolated buds. mRNA of alpha-, beta- and gamma-subunits was detected, the alpha-signal being the strongest. These results provide first molecular evidence for the presence of ENaC subunits in taste buds that were isolated from the posterior tongue and were free of epithelial contamination. In addition, we used immunohistochemistry to show ENaC-like reactivity in posterior tongue taste cells. Interestingly, the immunoreactivity was not predominantly apical but was intracellular and close to or at the basolateral membrane. The function of basolateral ENaC-type channels is unknown. Possibly, the channels are normally closed or of very low open probability in the resting state.

MDR1 in taste buds of rat vallate papilla: functional, immunohistochemical, and biochemical evidence

Multidrug resistance P-glycoprotein (MDR1) is a membrane protein of 150-170 kDa that catalyzes the ATP-driven efflux of hydrophobic xenobiotics, including fluorescent dyes, from cells. Expressed in many epithelial tissues and in the endothelia of the blood-brain barrier, the MDR1 protein provides major routes of detoxification. We found that taste cells of the rat vallate papilla (VP; posterior tongue) had only a slow increase in fluorescence due to uptake of the hydrophobic dye calcein acetoxymethyl ester. However, the development of fluorescence was accelerated two- to threefold by substrates and/or inhibitors of MDR1, such as verapamil, tamoxifen, and cyclosporin A, and by addition of the transport-blocking antibody to MDR1, UIC2. Western blots of vallate tissue rich in taste buds with the MDR1-specific monoclonal antibodies C219 and C494 revealed an immunoreactive protein at approximately 170 kDa. In contrast, the lingual epithelium surrounding the VP showed a much weaker band with these antibodies. Furthermore, using the antibodies C494 and UIC2 with tissue sections, MDR1-like immunoreactivity was found in taste cells. These results show that MDR1 is present and functional in vallate taste cells of the rat. MDR1-related transport may achieve active elimination of xenobiotics from the sensory cells and thereby protect the peripheral taste organs from potentially harmful molecules contained in an animal's food.

Sodium taste

The regulation of sodium metabolism is achieved by the adaptive sodium-saving capacities in epithelia and by hormones acting within the brain to modulate salt appetite. Taste, especially in rodents, has a sodium-specific component that provides a guiding function for salt intake. The taste responsiveness is not invariable, however, and may be modified in the case of sodium need. This review discusses emerging functional aspects of the peripheral and central branch of the salt sensory pathway.

Chemoreception: tasting the sweet and the bitter

Our understanding of the molecular basis of taste transduction has lagged behind that of other senses, but now a signalling protein-the G protein alpha subunit gustducin-has been shown to be taste-tissue specific and essential for both bitter and sweet tastes.

Blockade of epithelial Na+ channels by triamterenes - underlying mechanisms and molecular basis

The three subunits (alpha, beta, gamma) encoding for the rat epithelial Na+ channel (rENaC) were expressed in Xenopus oocytes, and the induced Na+ conductance was tested for its sensitivity to various triamterene derivatives. Triamterene blocked rENaC in a voltage-dependent manner, and was 100-fold less potent than amiloride at pH 7.5. At -90 mV and -40 mV, the IC50 values were 5 microM and 10 microM, respectively. The blockage by triamterene, which is a weak base with a pKa of 6.2, was dependent on the extracellular pH. The IC50 was 1 microM at pH 6.5 and only 17 microM at pH 8.5, suggesting that the protonated compound is more potent than the unprotonated one. According to a simple kinetic analysis, the apparent inhibition constants at -90 mV were 0.74 microM for the charged and 100.6 microM for the uncharged triamterene. The main metabolite of triamterene, p-hydroxytriamterene sulfuric acid ester, inhibited rENaC with an approximately twofold lower affinity. Derivatives of triamterene, in which the p-position of the phenylmoiety was substituted by acidic or basic residues, inhibited rENaC with IC50 values in the range of 0.1-20 microM. Acidic and basic triamterenes produced a rENaC blockade with a similar voltage and pH dependence as the parent compound, suggesting that the pteridinemoiety of triamterene is responsible for that characteristic. Expression of the rENaC alpha-subunit-deletion mutant, Delta278-283, which lacks a putative amiloride-binding site, induced a Na+ channel with a greatly reduced affinity for both triamterene and amiloride. In summary, rENaC is a molecular target for triamterene that binds to its binding site within the electrical field, preferably as a positively charged molecule in a voltage- and pH-dependent fashion. We propose that amiloride and triamterene bind to rENaC using very similar mechanisms.

Taste reception

Recent research on cellular mechanisms of peripheral taste has defined transduction pathways involving membrane receptors, G proteins, second messengers, and ion channels. Receptors for organic tastants received much attention, because they provide the specificity of a response. Their future cloning will constitute a major advance. Taste transduction typically utilizes two or more pathways in parallel. For instance, sweet-sensitive taste cells of the rat appear to respond to sucrose with activation of adenylyl cyclase, followed by adenosine 3',5'-cyclic monophosphate (cAMP)-dependent membrane events and Ca2+ uptake. The same cells respond differently to some artificial sweeteners, i.e., with activation of phospholipase C (PLC) followed by inositol 1,4,5-trisphosphate (IP3)-dependent Ca2+ release from intracellular stores. Some bitter tastants block K+ channels or initiate the cascade receptor G1 protein, PLC, IP3, and Ca2+ release or the cascade receptor alpha-gustducin, phosphodiesterase (PDE), cAMP decrease, and opening of cAMP-blocked channels. Membrane-permeant bitter tastants may elicit a cellular response by interacting with G protein, PLC, or PDE of the above cascades. Salt taste is initiated by current flowing into the taste cell through cation channels located in the apical membrane, even though basolateral channels may also contribute (following salt diffusion through paracellular pathways). In rodents, the Na+-specific component of salt taste is typically mediated by apical amiloride-sensitive Na+ channels, but less specific and not amiloride-sensitive taste components exist in addition. Sour taste may in part be mediated by amiloride-sensitive Na+ channels conducting protons, but other mechanisms certainly contribute. Thus the transduction of taste cells generally comprises parallel pathways. Furthermore, the transduction pathways vary with the location of taste buds on the tongue and, of course, across species of animals. To identify these pathways, to understand how they are controlled and why they evolved to this complexity are major goals of present research.

Changes in IP3 and cytosolic Ca2+ in response to sugars and non-sugar sweeteners in transduction of sweet taste in the rat

1. The transduction pathways of sweet-sensitive cells in rat circumvallate (CV) taste buds were investigated with assays for inositol 1,4,5-trisphosphate (IP3) and with Ca2+ imaging. Stimulation with the non-sugar sweeteners SC-45647 and saccharin rapidly increased the cellular content of IP3 by 400 pmol (mg protein)-1, while sucrose had a much smaller effect on IP3. As shown previously, sucrose, but not saccharin, increased the content of cyclic adenosine monophosphate (cAMP) of this preparation. 2. Stimulation of isolated CV taste buds with SC-45647 increased the cytosolic Ca2+ concentration ([Ca2+]i) by 56.7 +/- 3.2 nM (n = 181). Due to the non-confocality of the measuring system, these concentrations are underestimates. The increase in [Ca2+]i did not require the presence of extracellular Ca2+, suggesting that the Ca2+ release was from intracellular stores. 3. Individual cells responding to the non-sugar sweeteners with Ca2+ release also responded to sucrose and to forskolin with an increase in [Ca2+]i. Such cells did not respond to the bitter tastant denatonium chloride. 4. Responses to sucrose were abolished by lowering the Ca2+ concentration of the stimulus solution, indicating Ca2+ uptake from the extracellular medium. 5. The responses of sweet-sensitive cells to forskolin were also abolished when Ca2+ ions were omitted from the stimulus solution. They were partially inhibited by the presence of Co2+, Ni2+, D600 (methoxyverapamil) and amiloride, indicating multiple pathways of Ca2+ uptake activated by cAMP. 6. In conclusion, a sweet-sensitive cell of the rat responds to sucrose with an increase in cAMP and Ca2+ uptake, but to non-sugar sweeteners with an increase in IP3 and Ca2+ release. The increase in [Ca2+]i, common to both pathways, is presumably required for synaptic exocytosis and for signal termination.

Sweet and Salty: Transduction in Taste

Signal pathways in taste receptor cells reach from apical events, like binding of a tastant to a receptor, through intracellular processes and basolateral regenerative ion channel activity to the release of transmitter. The responses are now being investigated with patch clamping, monitoring of intracellular messengers including Ca2+, and molecular cloning.

Cyclic nucleotide-gated channels of rat olfactory receptor cells: divalent cations control the sensitivity to cAMP

cAMP-gated channels were studied in inside-out membrane patches excised from the apical cellular pole of isolated olfactory receptor cells of the rat. In the absence of divalent cations the dose-response curve of activation of patch current by cAMP had a KM of 4.0 microM at -50 mV and of 2.5 microM at +50 mV. However, addition of 0.2 or 0.5 mM Ca2+ shifted the KM of cAMP reversibly to the higher cAMP concentrations of 33 or 90 microM, respectively, at -50 mV. Among divalent cations, the relative potency for inducing cAMP affinity shifts was: Ca2+ > Sr2+ > Mn2+ > Ba2+ > Mg2+, of which Mg2+ (up to 3 mM) did not shift the KM at all. This potency sequence corresponds closely to that required for the activation of calmodulin. However, the Ca(2+)-sensitivity is lower than expected for a calmodulin-mediated action. Brief (60 s) transient exposure to 3 mM Mg2+, in the absence of other divalent cations, had a protective effect in that following washout of Mg2+, subsequent exposure to 0.2 mM Ca2+ no longer caused affinity shifts. This protection effect did not occur in intact cells and was probably a consequence of patch excision, possibly representing ablation of a regulatory protein from the channel cyclic nucleotide binding site. Thus, the binding of divalent cations, probably via a regulatory protein, controls the sensitivity of the cAMP-gated channels to cAMP. The influx of Ca2+ through these channels during the odorant response may rise to a sufficiently high concentration at the intracellular membrane surface to contribute to the desensitization of the odorant-induced response. The results also indicate that divalent cation effects on cyclic nucleotide-gated channels may depend on the sequence of pre-exposure to other divalent cations.

Properties of cyclic nucleotide-gated channels mediating olfactory transduction. Activation, selectivity, and blockage

Cyclic nucleotide-gated channels (cng channels) in the sensory membrane of olfactory receptor cells, activated after the odorant-induced increase of cytosolic cAMP concentration, conduct the receptor current that elicits electrical excitation of the receptor neurons. We investigated properties of cng channels from frog and rat using inside-out and outside-out membrane patches excised from isolated olfactory receptor cells. Channels were activated by cAMP and cGMP with activation constants of 2.5-4.0 microM for cAMP and 1.0-1.8 for cGMP. Hill coefficients of dose-response curves were 1.4-1.8, indicating cooperativity of ligand binding. Selectivity for monovalent alkali cations and the Na/Li mole-fraction behavior identified the channel as a nonselective cation channel, having a cation-binding site of high field strength in the pore. Cytosolic pH effects suggest the presence of an additional titratable group which, when protonated, inhibits the cAMP-induced current with an apparent pK of 5.0-5.2. The pH effects were not voltage dependent. Several blockers of Ca2+ channels also blocked olfactory cng channels. Amiloride, D 600, and diltiazem inhibited the cAMP-induced current from the cytosolic side. Inhibition constants were voltage dependent with values of, respectively, 0.1, 0.3, and 1 mM at -60 mV, and 0.03, 0.02, and 0.2 mM at +60 mV. Our results suggest functional similarity between frog and rat cng channels, as well as marked differences to cng channels from photoreceptors and other tissues.

Noninvasive recording of receptor cell action potentials and sustained currents from single taste buds maintained in the tongue: the response to mucosal NaCl and amiloride

Apical membrane currents were recorded from the taste pore of single taste buds maintained in the tongue of the rat, using a novel approach. Under a dissection microscope, the 150-microns opening of a saline-filled glass pipette was positioned onto single fungiform papillae, while the mucosal surface outside the pipette was kept dry. Electrical responses of receptor cells to chemical stimuli, delivered from the pipette, were recorded through the pipette while the cells remained undamaged in their natural environment. We observed monophasic transient currents of 10-msec duration and 10-100 pA amplitude, apparently driven by action potentials arising spontaneously in the receptor cells. When perfusing the pipette with a solution of increased Na but unchanged Cl concentration, a stationary inward current (from pipette to taste cell) of 50-900 pA developed and the collective spike rate of the receptor cells increased. At a mucosal Na concentration of 250 mM, the maximal collective spike rate of a bud was in the range of 6-10 sec-1. In a phasic/tonic response, the high initial rate was followed by an adaptive decrease to 0.5-2 sec-1. Buds of pure phasic response were also observed. Amiloride (30 microM) present in the pipette solution reversibly and completely blocked the increase in spike rate induced by mucosal Na. Amiloride also decreased reversibly the stationary current which depended on the presence of mucosal Na (inhibition constant near 1 microM). During washout of amiloride, spike amplitudes were first small, then increased, but always remained smaller than the amiloride-blockable stationary current of the bud.(ABSTRACT TRUNCATED AT 250 WORDS)

Current recording from sensory cilia of olfactory receptor cells in situ. II. Role of mucosal Na+, K+, and Ca2+ ions

Action potential-driven current transients were recorded from sensory cilia and used to monitor the spike frequency generated by olfactory receptor neurons, which were maintained in their natural position in the sensory epithelium. Both basal and messenger-induced activities, as elicited with forskolin or cyclic nucleotides, were dependent on the presence of mucosal Na+. The spike rate decreased to approximately 20% when mucosal Na+ was lowered from 120 to 60 mM (replaced by N-methyl-D-glucamine+), without clear changes in amplitude and duration of the recorded action potential-driven transients. Mucosal Ca2+ and Mg2+ blocked spike discharge completely when increased from 1 to 10 mM in Ringer solution. Lowering mucosal Ca2+ below 1 mM increased the spike rate. These results can be explained by the presence of a cyclic nucleotide-dependent, Ca(2+)-sensitive cation conductance, which allows a depolarizing Na+ inward current to flow through the apical membrane of in situ receptor cells. A conductance with these properties, thought to provide the receptor current, was first described for isolated olfactory cells by Nakamura and Gold (1987. Nature (Lond.). 325:442-444). The forskolin-stimulated spike rate decreased when l-cis-diltiazem, a known blocker of the cyclic nucleotide-dependent receptor current, was added to the mucosal solution. Spike rate also decreased when the mucosal K+ concentration was lowered. Mucosal Ba2+ and 4-aminopyridine, presumably by means of cell depolarization, rapidly increased the spike rate. This suggests the presence of apical K+ channels that render the receptor cells sensitive to the K+ concentration of the olfactory mucus. With a slower time course, mucosal Ba2+ and 4-aminopyridine decreased the amplitude and caused rectification of the fast current transients (prolongation of action potentials). Abolishment of the apical Na+ current (by removal of mucosal Na+), as indicated by a strong decrease in spike rate, could be counteracted by adding 10 mM Ba2+ or 1 mM 4-aminopyridine to the mucosal solution, which re-established spiking. Similarly, blockage of the apical cation conductance with 10 mM Ca could be counteracted by adding 10 mM Ba2+ or by raising the mucosal K+ concentration. Thus mucosal concentrations of Na+, K+, and Ca2+ will jointly affect the sensitivity of odor detection.

Current recording from sensory cilia of olfactory receptor cells in situ. I. The neuronal response to cyclic nucleotides

The olfactory mucosa of the frog was isolated, folded (the outer, ciliated side faced outward), and separately superfused with Ringers solution on each side. A small number of sensory cilia (one to three) were pulled into the orifice of a patch pipette and current was recorded from them. Fast bipolar current transients, indicating the generation of action potentials by the receptor cells, were transmitted to the pipette, mainly through the ciliary capacitance. Basal activity was near 1.5 spikes s-1. Exposure of apical membrane areas outside of the pipette to permeant analogues of cyclic nucleotides, to forskolin, and to phosphodiesterase inhibitors resulted in a dose-dependent acceleration of spike rate of all cells investigated. Values of 10-20 s-1 were reached. These findings lend further support to the notion that cyclic nucleotides act as second messengers, which cause graded membrane depolarization and thereby a graded increase in spike rate. The stationary spike rate induced by forskolin was very regular, while phosphodiesterase inhibitors caused (in the same cell) an irregular pattern of bursts of spikes. The response of spike rate was phasic-tonic in the case of strong stimulation, even when elicited by inhibitors of phosphodiesterase or by analogues of cyclic nucleotides that are not broken down by the enzyme. Thus, one of the mechanisms contributing to desensitization appears to operate at the level of the nucleotide-induced ciliary conductance. However, desensitization at this level was slow and only partial, in contrast to results obtained with isolated, voltage-clamped receptor cells.

Membrane currents in taste cells of the rat fungiform papilla. Evidence for two types of Ca currents and inhibition of K currents by saccharin

Taste buds were isolated from the fungiform papilla of the rat tongue and the receptor cells (TRCs) were patch clamped. Seals were obtained on the basolateral membrane of 281 TRCs, protruding from the intact taste buds or isolated by micro-dissection. In whole-cell configuration 72% of the cells had a TTX blockable transient Na inward current (mean peak amplitude 0.74 nA). All cells had outward K currents. Their activation was slower than for the Na current and a slow inactivation was also noticeable. The K currents were blocked by tetraethylammonium, Ba, and 4-aminopyridine, and were absent when the pipette contained Cs instead of K. With 100 mM Ba or 100 mM Ca in the bath, two types of inward current were observed. An L-type Ca current (ICaL) activated at -20 mV had a mean peak amplitude of 440 pA and inactivated very slowly. At 3 mM Ca the activation threshold of ICaL was near -40 mV. A transient T-type current (ICaT) activated at -50 mV had an average peak amplitude of 53 pA and inactivated with a time constant of 36 ms at -30 mV. ICaL was blocked more efficiently by Cd and D600 than ICaT. ICaT was blocked by 0.2 mM Ni and half blocked by 200 microM amiloride. In whole-cell voltage clamp, Na-saccharin caused (in 34% of 55 cells tested) a decrease in outward K currents by 21%, which may be expected to depolarize the TRCs. Also, Na-saccharin caused some taste cells to fire action potentials (on-cell, 7 out of 24 cells; whole-cell, 2 out of 38 cells responding to saccharin) of amplitudes sufficient to activate ICaL. Thus the action potentials will cause Ca inflow, which may trigger release of transmitter.

Single unit recording from olfactory cilia

Sensory cilia from olfactory receptor cells can be pulled into a patch pipette located above the mucus layer of an olfactory mucosa. While the pipette does not form a tight electrical seal with the ciliary membrane, it nevertheless allows to record current transients driven by action potentials arising in the olfactory neuron. This method is an alternative to single-unit-recording with electrodes pushed into the mucosa and, in some respects, to patch clamp recordings from isolated olfactory cells. Its advantage is technical simplicity and minimal disturbance of the neuron from which signals are derived. Less than 5% of the chemosensitive apical surface of the neuron is covered by the pipette. The neuron remains in situ and its cilia remain covered with some mucus. (However, mucus is in part dissolved by the bathing solution). Odorant thresholds in the picomolar range were thus obtained.

Single chloride channels in colon mucosa and isolated colonic enterocytes of the rat

Chloride channels from rat colonic enterocytes were studied using the patch-clamp technique. After removal of mucus, inside-out patches were excised from the apical membrane of intact epithelium located at the luminal surface. They contained spontaneously switching Cl- channels with a conductance of 35-40 pS. The channels were blocked reversibly by anthracene-9-carboxylic acid (1mM). In excised patches from single enterocytes, isolated by calcium removal, the Cl- channels were studied in more detail. The I-V relation was linear between +/- 80 mV. The selectivity was I- greater than Br- greater than Cl- = NO3- greater than F- = HCO3-. Thirty pS Cl- channels were also found on the basolateral membrane of crypts isolated by brief calcium removal. The I-V curve of these Cl- channels was also linear. The results provide direct evidence for the existence of Cl- channels in the apical membrane of surface cells in colonic mucosa. The properties of these channels are similar to those previously observed when incorporating membrane vesicles into planar lipid bilayers. Both results support the validity of the theoretical models describing intestinal secretion.

Amiloride-blockable sodium currents in isolated taste receptor cells

Isolated taste receptor cells from the frog tongue were investigated under whole-cell patch-clamp conditions. With the cytosolic potential held at -80 mV, more than 50% of the cells had a stationary inward Na current of 10 to 700 pA in Ringer's solution. This current was in some cells partially, in others completely, blockable by low concentrations of amiloride. With 110 mM Na in the external and 10 mM Na in the internal solution, the inhibition constant of amiloride was (at -80 mV) near 0.3 microM. In some cells the amiloride-sensitive conductance was Na specific; in others it passed both Na and K. The Na/K selectivity (estimated from reversal potentials) varied between 1 and 100. The blockability by small concentrations of amiloride resembled that of channels found in some Na-absorbing epithelia, but the channels of taste cells showed a surprisingly large range of ionic specificities. Receptor cells, which in situ express these channels in their apical membrane, may be competent to detect the taste quality "salty." The same cells also express TTX-blockable voltage-gated Na channels.

Odorant response of isolated olfactory receptor cells is blocked by amiloride

Olfactory receptor cells were isolated from the nasal mucosa of Rana esculenta and patch clamped. Best results were obtained with free-floating cells showing ciliary movement. 1) On-cell mode: Current records were obtained for up to 50 min. Under control conditions they showed only occasional action potentials. The odorants cineole, amyl acetate and isobutyl methoxypyrazine were applied in saline by prolonged superfusion. At 500 nanomolar they elicited periodic bursts of current transients arising from cellular action potentials. The response was rapidly, fully and reversibly blocked by 50 microM amiloride added to the odorant solution. With 10 microM amiloride, the response to odorants was only partially abolished. 2) Whole-cell mode: Following breakage of the patch, the odorant response was lost within 5 to 15 min. Prior to this, odorants evoked a series of slow transient depolarizations (0.1/sec, 45 mV peak to peak) which reached threshold and thus elicited the periodic discharge of action potentials. These slow depolarizing waves were reversibly blocked by amiloride, which stabilized the membrane voltage between -80 and -90 mV. We conclude that amiloride inhibits chemosensory transduction of olfactory receptor cells, probably by blocking inward current pathways which open in response to odorants.

Transduction in taste receptor cells requires cAMP-dependent protein kinase

In taste chemoreception, cyclic adenosine monophosphate (cAMP) appears to be one of the intracellular messengers coupling reception of stimulus to the generation of the response. The recent finding that sweet agents cause a GTP-dependent generation of cAMP poses the question of how this cytosolic messenger acts at the membrane of taste receptor cells. We have shown that cAMP causes a substantial depolarization in these cells. Here we show with whole-cell recordings and inside-out membrane patches that the depolarization caused by cAMP is accounted for by the action of cAMP-dependent protein kinase, which inactivates potassium channels predominantly of 44 pS conductance. Thus, intracellular signalling of the gustatory cells differs from that of olfactory and photoreceptor cells, where cyclic nucleotides control unspecific channels by binding to them rather than by inducing their phosphorylation.

Signalling in taste receptor cells: cAMP-dependent protein kinase causes depolarization by closure of 44 pS K-channels

1. In whole-cell patch-clamp recordings cytosolic cAMP causes a substantial depolarization of taste receptor cells isolated from the frog tongue. The depolarization requires the presence of ATP in the cell and is suppressed by protein kinase inhibitor. 2. The depolarization also develops in the absence of cAMP while the catalytic subunit of the kinase is allowed to diffuse into the cell in the presence of ATP. 3. In membrane patches excised from these cells the catalytic subunit is found to inactivate K-channels of 44 pS conductance, presumably by phosphorylation. 4. It appears that cAMP is one of the intracellular messengers in gustatory chemoreception, and that it causes membrane depolarization through activation of a protein kinase which controls the activity of one set of K-channels.

Action potentials in epithelial taste receptor cells induced by mucosal calcium

Chemosensory cells in the taste bud of the tongue of Necturus generate action potentials in response to electrical stimulation through a microelectrode, as recently described by Roper (Science, 220: 1311-1312, 1983). We report that the epithelial receptor cells also respond to 10 mM CaCl2, applied to the mucosal surface, with a depolarization which elicits action potentials when a threshold of -50 mV is reached. Since CaCl2 is one of the taste stimuli in amphibia, the firing of action potentials by chemoreceptor cells may be part of the signal chain in gustatory reception of Ca ions.

Patch-clamp study of isolated taste receptor cells of the frog

Taste discs were dissected from the tongue of R. ridibunda and their cells dissociated by a collagenase/low Ca/mechanical agitation protocol. The resulting cell suspension contained globular epithelial cells and, in smaller number, taste receptor cells. These were identified by staining properties and by their preserved apical process, the tip of which often remained attached to an epithelial (associated) cell. When the patch pipette contained 110 mM KCl and the cells were superfused with NaCl Ringer's during whole-cell recording, the mean zero-current potential of 22 taste receptor cells was -65.2 mV and the slope resistance 150 to 750 M omega. Pulse-depolarization from a holding voltage of -80 mV activated a transient TTX-blockable inward Na current. Activation became noticeable at -25 mV and was half-maximal at -8 mV. Steady-state inactivation was half-maximal at -67 mV and complete at -50 mV. Peak Na current averaged -0.5 nA/cell. The Ca-ionophore A23187 shifted the activation and inactivation curve to more negative voltages. Similar shifts occurred when the pipette Ca was raised. External Ni (5 mM) shifted the activation curve towards positive voltages by 10 mV. Pulse depolarization also activated outward K currents. Activation was slower than that of Na current and inactivation slower still. External TEA (7.5 mM) and 4-amino-pyridine (1 mM) did not block, but 5 mM Ba blocked the K currents. K-tail currents were seen on termination of depolarizing voltage pulses. A23187 shifted the IK(V)-curve to more negative voltages. Action potentials were recorded when passing pulses of depolarizing outward current. Of the frog gustatory stimulants, 10 mM Ca caused a reversible 5- to 10-mV depolarization in the current-clamp mode. Quinine (0.1 mM, bitter) produced a reversible depolarization accompanied by a full block of Na current and, with slower time-course, a partial block of K currents. Cyclic AMP (5 mM in the external solution or 0.5 microM in the pipette) caused reversible depolarization (to -40 to -20 mV) due to partial blockage of K currents, but only if ATP was added to the pipette solution. Similar responses were elicited by stimulating the adenylate cyclase with forskolin. Blockage of cAMP-phosphodiesterase enhanced the response to cAMP. These results suggest that cAMP may be one of the cytosolic messengers in taste receptor cells. Replacement of ATP by AMP-PNP in the pipette abolished the depolarizing response to cAMP.(ABSTRACT TRUNCATED AT 400 WORDS)

An amiloride-sensitive Na+ conductance in the basolateral membrane of toad urinary bladder

Exposing the apical membrane of toad urinary bladder to the ionophore nystatin lowers its resistance to less than 100 omega cm2. The basolateral membrane can then be studied by means of transepithelial measurements. If the mucosal solution contains more than 5 mM Na+, and serosal Na+ is substituted by K+, Cs+, or N-methyl-D-glucamine, the basolateral membrane expresses what appears to be a large Na+ conductance, passing strong currents out of the cell. This pathway is insensitive to ouabain or vanadate and does not require serosal or mucosal Ca2+. In Cl-free SO2-(4) Ringer's solution it is the major conductive pathway in the basolateral membrane even though the serosal side has 60 mM K+. This pathway can be blocked by serosal amiloride (Ki = 13.1 microM) or serosal Na+ ions (Ki approximately 10 to 20 mM). It also conducts Li+ and shows a voltage-dependent relaxation with characteristic rates of 10 to 20 rad sec-1 at 0 mV.

Structure-activity relationship of amiloride analogs as blockers of epithelial Na channels: II. Side-chain modifications

The overall on- and off-rate constants for blockage of epithelial Na channels by amiloride analogs were estimated by noise analysis of the stationary Na current traversing frog skin epithelium. The (2-position) side chain structure of amiloride was varied in order to obtain structure/rate constant relationships. Hydrophobic chain elongations (benzamil and related compounds of high blocking potency) increase the stability of the blocking complex (lowered off-rate), explained by attachment of the added phenyl moiety to a hydrophobic area near the site of side chain interaction with the channel protein. Some other chain modifications show that the on-rate, which is smaller than a diffusion-limited rate, varies with side chain structure. In several cases this effect is not attributable to steric hindrance on encounter, and implies that the side chain interacts briefly with the channel protein (encounter complex) before the main blocking position of the molecule is attained. The encounter complex must be labile since the overall rate constants of blockage are not concentration-dependent. In two cases, changes at the 2-position side chain and at other ring ligands, with known effects on the blocking rate constants, could be combined in one analog. The rate constants of blocking by the resulting compounds indicate that the structural changes have additive effects in terms of activation energies. Along with other observations (voltage dependence of the rate constants and competition with the transported Na ion), these results suggest a blocking process of at least two steps. It appears that initially the 2-position side chain invades the outward-facing channel entrance, establishing a labile complex. Then the molecule is either released completely (no block) or the 6-ligand of the pyrazine ring gains access to its receptor counterpart, thus establishing the blocking complex, the lifetime of which is strongly determined by the electronegativity of the 6-ligand.

Properties of an anion-selective channel from rat colonic enterocyte plasma membranes reconstituted into planar phospholipid bilayers

Vesicles derived from epithelial cells of the colonic mucosa of the rat were fused to planar phospholipid bilayer membranes, revealing spontaneously switching anion-conducting channels of 50 pS conductance (at -30 mV with 200 mM Cl- each side). The equilibrium selectivity series was I- (1.7)/Br- (1.3)/Cl- (1.0)/F- (0.4)/HCO3- (0.4)/Na (less than 0.11). Only one dominant open-state conductance could be resolved, which responded linearly to Cl- concentrations up to 600 mM. The single-channel current-voltage curve was weakly rectifying with symmetrical solutions. When 50 mV were exceeded at the high-conductance branch of the curve, switching was arrested in the closed state. At more moderate voltages (+/- 40 mV) kinetics were dominated by one open state of about 35-msec lifetime and two closed states of about 2 and 9-msec lifetime. Of these, the more stable closed state occurred less often. At these voltages one additional closed state of significantly longer lifetime (greater than 0.5 sec) was observed.

Voltage dependence of Na channel blockage by amiloride: relaxation effects in admittance spectra

Amiloride, present in the mucosal solution, causes the appearance of a distinct additional dispersion in the admittance spectrum of the apical membrane of toad urinary bladder. The parameters of this dispersion (characteristic frequency, amplitude) change with amiloride concentration and with membrane voltage. They allow the calculation of the overall rate constants for Na channel blockage by the positively charged form of amiloride, and the voltage dependence of these rate constants. The on-rate of blockage increases and the off-rate decreases when the membrane surface to which cationic amiloride has access, is made more positive. This result is suggestive of a blocking model where the cationic amidino group of amiloride, depending on its charge, senses 10 to 13% of the membrane voltage while invading the channel entrance by a single-step process, and rests at an electrical distance corresponding to 24 to 30% of membrane voltage while occupying the blocking position.

Angiostrongylosis in a greyhound

Angiostrongylus vasorum infection was diagnosed at necropsy of a Greyhound imported from Ireland. Granulomatous masses and pulmonary arterial thrombosis were associated with adult and larval stages of metastrongyle nematodes. Hemorrhages, widespread in subcutaneous tissue and muscle masses and at serosal surfaces, were suggestive of the onset of the bleeding disorder that has been seen in angiostrongylosis in Europe. The mollusks that can serve as intermediate hosts are known to be common in the United States, and therefore establishment of this parasite from imported racing or breeding stock is possible.

Pattern analysis of 5S rRNA

Some 200 different 5S rRNA sequences from eubacteria, chloroplasts, mitochondria, archaebacteria, and eukaryotes were analyzed for evolutionary kinship relationships and associated sequential features. Group-specific occupation schemes for the 149 positions of an overall alignment were established. Eubacterial, archaebacterial, and intermediate occupation schemes all yield a strongly biased base triplet pattern in one of the three possible reading frames strongest for eubacterial, chloroplastic, and archaebacterial, but still detectable for mitochondrial and eukaryotic cytoplasmic sequences. The frequency of triplets decays in the order RNY greater than RNR greater than YNY greater than YNR; R being a purine (guanine or adenine), Y is a pyrimidine (cytosine or uracil), and N is any base. A strong preference for guanine or cytosine was found in all triplet positions. The effects show no exceptions and are clearly above the level of statistical fluctuations.

Structure-activity relationship of amiloride analogs as blockers of epithelial Na channels: I. Pyrazine-ring modifications

The overall on- and off-rate constants for blocking epithelial Na channels by amiloride analogs were estimated by noise analysis of frog skin epithelium. The substituents at position-5 and -6 of the pyrazine ring of amiloride were varied in order to obtain the structure/rate constant relationship. (1) The off-rate constant increases with halo-substitutions at position-6 in the order Cl less than Br less than l less than F less than H. Substitution of Cl by H lowers the standard free energy of activation of the off-step by 2.3 kcal mol-1. The on-rate constant is not affected. Apparently the substituent at ring position-6 controls the duration of attachment in the blocking position. pKa considerations show that the duration is longer when the 6-substituent is more negatively polarized. We suggest that this substituent binds to the receptor by virtue of its electronegativity. (2) In contrast, replacement of the adjacent 5-amino group (electron donor) by H or Cl affects both the on-rate and the off-rate. The dual effect may be explained by a decrease of the electronic charge at more remote parts of the molecule (on-rate decrease), as well as at the 6-position (off-rate increase). Apparently the 5-amino group stabilizes the blocking position by increasing the electron density on the 6-ligand.

Voltage dependence of the blocking rate constants of amiloride at apical Na channels

The overall rate constants of blockage of apical Na channels by amiloride, previously determined by noise analysis, were obtained in macroscopic relaxation experiments with toad urinary bladders exposed to a mucosal Na activity of 60 mM. By the use of step voltage perturbations and by admittance analysis we show that the on-rate constant of blockage increases, and the off-rate constant decreases when the outer membrane surface is made more positive. In the frame-work of a plug-type blocking model the results imply that the cationic amidino group of amiloride senses about 10% of the membrane voltage while invading the channel entrace and slightly more than 10% while leaving the entrance.