Evolution of mechanics in α-helical peptide conjugated linear- and star-block PEG.

We have designed a peptide conjugated poly-ethylene glycol (PEG) bioconjugate system that allows us to examine the intra- and inter-molecular dynamics of gelation. We measure the kinetics of gelation for end-functionalized linear- and star-architectures, and we correlate the gelation behavior with the molecular structure and self-association. The 23-amino acid peptide sequence is known to form a coiled-coil structure as a function of the solution's electrolyte concentration, and the two topologies of the PEG are peptide end-functionalized to examine formation of supramolecular assemblies. Subsequently, microrheology is used to evaluate the dynamics of self-assembly and the gelation time-scales. This study shows that the dynamics of peptide folding and assembly for linear-PEG conjugated systems yield a percolated network, but the star-PEG conjugated systems yield discrete assemblies and remain viscous. The results suggest that the degree of intra- and inter-molecular folding defines the critical gel behavior of the supramolecular system.

Do calcium waves propagate between cells and synchronize alternating calcium release in rat ventricular myocytes?

The aim was to investigate the propagation of Ca(2+) waves between cells and determine whether this synchronizes alternating Ca(2+) release between cells. Experiments were carried out on electrically coupled cell pairs; spontaneous Ca(2+) waves were produced by elevating external Ca(2+). There was a significant difference in the ability of these waves to propagate between cells depending on the orientation of the pairs. Although almost all pairs connected by side-to-side contacts showed propagating Ca(2+) release, this was very uncommon in end-to-end cell pairs. Confocal studies showed that there was a gap at the intercalated disc consisting of cell membranes and a region of cytoplasm devoid of sarcoplasmic reticulum. This gap was 2.3 µm in length and is suggested to interfere with Ca(2+) wave propagation. The gap measured was much smaller between side-to-side contacts: 1.5 µm and so much less likely to interfere with propagation. Subsequent experiments investigated the synchronization between cells of Ca(2+) alternans produced by small depolarizing pulses. Although this alternation results from beat-to-beat alternation of intracellular Ca(2+) wave propagation, there was no evidence that propagation of Ca(2+) waves between cells contributed to synchronization of this alternans.

Changes of SERCA activity have only modest effects on sarcoplasmic reticulum Ca2+ content in rat ventricular myocytes.

Changes of the activity of the sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA) affect the amplitude of the systolic Ca(2+) transient and thence cardiac contractility. This is thought to be due to alterations of SR Ca(2+) content. Recent work on mice in which the expression of SERCA is decreased found that a large reduction of SERCA expression resulted in a proportionately much smaller decrease of SR Ca(2+) content. The aim of the current work was to investigate the quantitative nature of the dependence of both the amplitude of the systolic Ca(2+) transient and SR Ca(2+) content on SERCA activity during acute partial inhibition of SERCA. Experiments were performed on rat ventricular myocytes. Brief application of thapsigargin (1 µm) resulted in a decrease of SERCA activity as measured from the rate of decay of the systolic Ca(2+) transient. This was accompanied by a decrease in the amplitude of the systolic Ca(2+) transient which was linearly related to that of SERCA activity. However, the fractional decrease in the SR Ca(2+) content was much less than that of SERCA activity. On average SR Ca(2+) content was proportional to SERCA activity raised to the 0.38 ± 0.07 power. This shallow dependence of SR content on SERCA activity arises because Ca(2+) release is a steep function of SR Ca(2+) content. In contrast SR Ca(2+) content was increased 4.59 ± 0.40 (n = 8)-fold by decreasing ryanodine receptor opening with tetracaine (1 mm). Therefore a modest decrease of SR Ca(2+) content results in a proportionately larger fall of Ca(2+) release from the SR which can balance a larger initiating decrease of SERCA. In conclusion, the shallow dependence of SR Ca(2+) content on SERCA activity is expected for a system in which small changes of SR Ca(2+) content produce larger effects on the amplitude of the systolic Ca(2+) transient.

What role does modulation of the ryanodine receptor play in cardiac inotropy and arrhythmogenesis?

In this article we review the role of the Ryanodine Receptor (RyR) in cardiac inotropy and arrhythmogenesis. Most of the calcium that activates cardiac contraction comes from the sarcoplasmic reticulum (SR) from where it is released through the RyR. The amplitude of the systolic Ca transient depends steeply on the SR Ca content and it is therefore important that SR content be regulated. This regulation occurs via changes of SR Ca content affecting systolic Ca and thence sarcolemmal Ca fluxes. In the steady state, the cardiac myocyte must be in Ca flux balance on each beat and this has implications for understanding even simple inotropic manoeuvres. The main part of the review considers the effects of modulating the RyR on systolic Ca. Potentiation of RyR opening produces an increase of the amplitude of the Ca transient but this effect disappears within a few beats because the increased sarcolemmal efflux of Ca decreases SR Ca content. We conclude that it is therefore unlikely that potentiation of the RyR by phosphorylation plays a dominant role in the actions of positive inotropic agents such as beta-adrenergic stimulation. Some cardiac arrhythmias result from release of Ca from the SR in the form of waves. This is best known to occur when the SR is overloaded with calcium. Mutations in the RyR also produce cardiac arrhythmias attributed to Ca waves due to leaky RyRs and a similar leak has been suggested to contribute to arrhythmias in heart failure. We show that, due to compensatory changes of SR Ca content, simply making the RyR leaky does not produce Ca waves in the steady state and that SR Ca content is critical in determining whether Ca waves occur.

Reducing ryanodine receptor open probability as a means to abolish spontaneous Ca2+ release and increase Ca2+ transient amplitude in adult ventricular myocytes.

The aim of this work was to investigate whether it is possible to remove arrhythmogenic Ca2+ release from the sarcoplasmic reticulum that occurs in calcium overload without compromising normal systolic release. Exposure of rat ventricular myocytes to isoproterenol (1 micromol/L) resulted in an increased amplitude of the systolic Ca2+ transient and the appearance of waves of diastolic Ca2+ release. Application of tetracaine (25 to 50 micromol/L) decreased the frequency or abolished the diastolic Ca2+ release. This was accompanied by an increase in the amplitude of the systolic Ca2+ transient. Cellular Ca2+ flux balance was investigated by integrating Ca2+ entry (on the L-type Ca2+ current) and efflux (on Na-Ca2+ exchange). Isoproterenol increased Ca2+ influx but failed to increase Ca2+ efflux during systole (because of the abbreviation of the duration of the Ca2+ transient). To match this increased influx the bulk of Ca2+ efflux occurred via Na-Ca2+ exchange during a diastolic Ca2+ wave. Subsequent application of tetracaine increased systolic Ca2+ efflux and abolished the diastolic efflux. The increase of systolic efflux in tetracaine resulted from both increased amplitude and duration of the systolic Ca2+ transient. In the presence of isoproterenol, those Ca2+ transients preceded by diastolic release were smaller than those where no diastolic release had occurred. When tetracaine was added, the amplitude of the Ca2+ transient was similar to those in isoproterenol with no diastolic release and larger than those preceded by diastolic release. We conclude that tetracaine increases the amplitude of the systolic Ca2+ transient by removing the inhibitory effect of diastolic Ca2+ release.

Na/Ca exchange: regulator of intracellular calcium and source of arrhythmias in the heart.

The major effect of Na/Ca exchange (NCX) on the systolic Ca transient is secondary to its effect on the Ca content of the sarcoplasmic reticulum (SR). SR Ca content is controlled by a mechanism in which an increase of SR Ca produces an increase in the amplitude of the systolic Ca transient. This, in turn, increases Ca efflux on NCX as well as decreasing entry on the L-type current resulting in a decrease of both cell and SR Ca content. This control mechanism also changes the response to other maneuvers that affect excitation-contraction coupling. For example, potentiating the opening of the SR Ca release channel (ryanodine receptor, RyR) with caffeine produces an immediate increase in the amplitude of the systolic Ca transient. However, this increases efflux of Ca from the cell on NCX and then decreases SR Ca content until a new steady state is reached. Changing the activity of NCX (by decreasing external Na) changes the level of SR Ca reached by this mechanism. If the cell and SR are overloaded with Ca then Ca waves appear during diastole. These waves activate the electrogenic NCX and thereby produce arrhythmogenic-delayed afterdepolarizations. A major challenge is how to remove this arrhythmogenic Ca release without compromising the normal systolic release. We have found that application of tetracaine to decrease RyR opening can abolish diastolic release while simultaneously potentiating the systolic release.

A cost analysis of the establishment of a dedicated orthopaedic outpatient injection clinic at a single institution.

INTRODUCTION: Traditionally orthopaedic injections were performed in a theatre setting. A dedicated outpatient injection clinic was established at our institution to attempt to provide injections more cost effectively. Our aim was to perform a cost analysis of orthopaedic injections performed in theatre, compared to those performed in a dedicated OPD injection clinic. METHODS: Patient data for all orthopaedic injections performed at a single institution from 2013 to 2014 was obtained using HIPE data. A detailed breakdown of costings for two scenarios; those performed in theatre and those in the dedicated OPD injection clinic was obtained from the hospital finance department. A unit cost per injection for theatre and OPD was derived from this financial information. RESULTS: A total of 487 injections were performed in 2013, with 491 performed in 2014. 134 (27.5%) injections were performed in the OPD in 2013 compared to 388 (79%) in 2014. The unit cost per injection was calculated as €52.13 for theatre and €23.85 for OPD, this represented a 115% decrease in cost per injection. CONCLUSION: The creation of a dedicated orthopaedic injection clinic resulted in considerable cost savings at our institution. We propose this may be a more cost-efficient model for delivery of injections in the orthopaedic setting.

Altered cardiac sarcoplasmic reticulum function of intact myocytes of rat ventricle during metabolic inhibition.

Changes in the behavior of the sarcoplasmic reticulum (SR) in rat ventricular myocytes were investigated under conditions of metabolic inhibition using laser-scanning confocal microscopy to measure intracellular Ca(2+) and the perforated patch-clamp technique to measure SR Ca(2+) content. Metabolic inhibition had several effects on SR function, including reduced frequency of spontaneous releases of Ca(2+) (sparks and waves of Ca(2+)-induced Ca(2+) release), increased SR Ca(2+) content (79.4+/-5.7 to 115.2+/-6.6 micromol/L cell volume [mean+/-SEM; P:<0.001]), and, after a wave of Ca(2+) release, slower reuptake of Ca(2+) into the SR (rate constant of fall of Ca(2+) reduced from 8.5+/-1.1 s(-)(1) in control to 5.2+/-0.4 s(-)(1) in metabolic inhibition [P:<0.01]). Inhibition of L-type Ca(2+) channels with Cd(2+) (100 micromol/L) did not reproduce the effects of metabolic inhibition on spontaneous Ca(2+) sparks. These results are evidence of inhibition of both Ca(2+) release and reuptake mechanisms. Reduced frequency of release could be attributable to either of these effects, but the increased SR Ca(2+) content at the time of reduced frequency of spontaneous release of Ca(2+) shows that the dominant effect of metabolic inhibition is to inhibit release of Ca(2+) from the SR, allowing the accumulation of greater than normal amounts of Ca(2+). In the context of ischemia, this extra accumulation of Ca(2+) would present a risk of potentially arrhythmogenic, spontaneous release of Ca(2+) on reperfusion of the tissue.

Depressed ryanodine receptor activity increases variability and duration of the systolic Ca2+ transient in rat ventricular myocytes.

Sarcoplasmic reticulum (SR) Ca2+ release, through the ryanodine receptor (RyR), is essential for the systolic Ca2+ transient and thus the cardiac contractile function. The aim of this study was to examine the effects on the spatial organization of the systolic Ca2+ transient of depressing RyR open probability (P(o)) with tetracaine or intracellular acidification. Voltage-clamped, fluo-3-loaded myocytes were studied using confocal microscopy. Depressing RyR P(o) increased the variability of the Ca2+ transient amplitude between different regions of the cell. This variability often produced alternans with a region producing large and small transients alternately. In addition, the raising phase of the Ca2+ transient became biphasic. The initial phase was constant but the second was variable and propagated as a wave through part of the cell. That both phases involved SR Ca2+ release was shown by their reduction by caffeine. Regional [Ca2+]i alternans was accompanied by a much smaller degree of alternans at the whole cell level. We suggest that, in tetracaine or acidosis, the initial phase of the Ca2+ transient results from Ca2+ release via RyRs directly activated by adjacent L-type Ca2+ channels. At some sites, this will activate neighboring RyRs and a Ca2+ wave will propagate via activation of other RyRs. This work is the first demonstration that decreased RyR P(o) alone can produce disarray of the Ca2+ release process and initiate alternans.

Integrative analysis of calcium cycling in cardiac muscle.

The control of intracellular calcium is central to regulation of contractile force in cardiac muscle. This review illustrates how analysis of the control of calcium requires an integrated approach in which several systems are considered. Thus, the calcium content of the sarcoplasmic reticulum (SR) is a major determinant of the amount of Ca(2+) released from the SR and the amplitude of the Ca(2+) transient. The amplitude of the transient, in turn, controls Ca(2+) fluxes across the sarcolemma and thence SR content. This control of SR content influences the response to maneuvers that modify, for example, the properties of the SR Ca(2+) release channel or ryanodine receptor. Specifically, modulation of the open probability of the ryanodine receptor produces only transient effects on the Ca(2+) transient as a result of changes of SR content. These interactions between various Ca(2+) fluxes are modified by the Ca(2+) buffering properties of the cell. Finally, we predict that, under some conditions, the above interactions can result in instability (such as alternans) rather than ordered control of contractility.

The control of sarcoplasmic reticulum Ca content in cardiac muscle.

Most of the calcium that activates contraction in the heart comes from the sarcoplasmic reticulum (SR) and it is therefore essential to control the SR Ca content. SR Ca content reflects the balance between uptake (via the SR Ca-ATPase, SERCA) and release, largely via the ryanodine receptor (RyR). Unwanted changes of SR Ca are prevented because, for example, an increase of SR Ca content increases the amplitude of the systolic Ca transient and this, in turn, results in increased loss of Ca from and decreased Ca entry into the cell thereby restoring cell and SR Ca towards control levels. We discuss the parameters that affect the steady level of SR Ca and how these may change in heart failure. Finally, we discuss disordered Ca regulation with particular emphasis on the condition of alternans where successive heartbeats alternate in amplitude. This behaviour can be explained by excessive feedback gain in the processes controlling SR Ca.

The relative contributions of different intracellular and sarcolemmal systems to relaxation in rat ventricular myocytes.

OBJECTIVE: The aim was to estimate the relative contributions of the various intracellular and sarcolemmal systems to the relaxation of the systolic calcium transient. METHODS: The experiments were performed on isolated rat ventricular myocytes. The cells were loaded with the fluorescent indicator indo-1 in order to measure [Ca2+]i. RESULTS: The application of caffeine to release calcium from the sarcoplasmic reticulum produced a rise of [Ca2+]i which decayed about 7-8 times more slowly than the electrically stimulated calcium transient. This suggests that the sarcoplasmic reticulum accounts for about 87% of the calcium removal. The rate of decay of the caffeine response was decreased to about 33% of the control by inhibiting the Na-Ca exchange with Ni2+. In the presence of Ni2+ the rate could be inhibited further by inhibiting either the sarcolemmal Ca-ATPase (by increasing extracellular calcium concentration, [Ca2+]o) or the mitochondria (with FCCP and oligomycin). The relative contributions of the various processes were estimated to be: sarcoplasmic reticulum 87%, mitochondria 1.7%, Na-Ca 8.7%, sarcolemmal Ca-ATPase 2.6%. CONCLUSIONS: These experiments show that the Na-Ca exchange accounts for 67% of the calcium removal not mediated by the sarcoplasmic reticulum. This is a smaller fraction than in rabbit cardiac cells and highlights the importance of the Ca-ATPase in the rat heart.

Effects of eicosapentaenoic acid on cardiac SR Ca(2+)-release and ryanodine receptor function.

n-3 polyunsaturated fatty acids (PUFAs) can prevent life-threatening arrhythmias but the mechanisms responsible have not been established. There is strong evidence that part of the antiarrhythmic action of PUFAs is mediated through inhibition of the Ca(2+)-release mechanism of the sarcoplasmic reticulum (SR). It has also been shown that PUFAs activate protein kinase A (PKA) and produce effects in the cardiac cell similar to beta-adrenergic stimulation. We have investigated whether the inhibitory effect of PUFAs on the Ca(2+)-release mechanism is caused by direct inhibition of the SR Ca(2+)-release channel/ryanodine receptor (RyR) or requires activation of PKA. Experiments in intact cells under voltage-clamp show that the n-3 PUFA eicosapentaenoic acid (EPA) is able to reduce the frequency of spontaneous waves of Ca(2+)-release while increasing SR Ca(2+) content even when PKA activity is inhibited with H-89. This suggests that the EPA-induced inhibition of SR Ca(2+)-release is not dependent on activation of PKA. Consistent with this, single-channel studies demonstrate that EPA (10-100 microM), but not saturated fatty acids, reduce the open probability (Po) of the cardiac RyR incorporated into phospholipid bilayers. EPA also inhibited the binding of [3H]ryanodine to isolated heavy SR. Our results indicate that direct inhibition of RyR channel gating by PUFAs play an important role in the overall antiarrhythmic properties of these compounds.

The control of Ca release from the cardiac sarcoplasmic reticulum: regulation versus autoregulation.

This review discusses the mechanism and regulation of Ca release from the cardiac sarcoplasmic reticulum. Ca is released through the Ca release channel or ryanodine receptor (RyR) by the process of calcium-induced Ca release (CICR). The trigger for this release is the L-type Ca current with a small contribution from Ca entry on the Na-Ca exchange. Recent work has shown that CICR is controlled at the level of small, local domains consisting of one or a small number of L-type Ca channels and associated RyRs. Ca efflux from the s.r. in one such unit is seen as a 'spark' and the properties of these sparks produce controlled Ca release from the s.r. A major factor controlling the amount of Ca released from the s.r. and therefore the magnitude of the systolic Ca transient is its Ca content. The Ca content depends on both the properties of the s.r. and the cytoplasmic Ca concentration. Changes of s.r. Ca content and the Ca released affect the sarcolemmal Ca and Na-Ca exchange currents and this acts to control cell Ca loading and the s.r. Ca content. The opening probability of the RyR can be regulated by various physiological mediators as well as pharmacological compounds. However, it is shown that, due to compensatory changes of s.r. Ca, modifiers of the RyR only produce transient effects on systolic Ca. We conclude that, although the RyR can be regulated, of much greater importance to the control of Ca efflux from the s.r. are effects due to changes of s.r. Ca content.

The effect of 2,5-di-(tert-butyl)-1,4-benzohydroquinone (TBQ) on intracellular Ca2+ handling in rat ventricular myocytes.

2,5-Di-(tert-butyl)-1,4-benzohydroquinone (TBQ) is a reversible inhibitor of SERCA, potentially making it a useful tool to study the effects of SERCA inhibition in cardiac cells. However, it is unknown if TBQ also has effects on other components of ventricular Ca handling. The aim of these experiments was to characterise the effects of TBQ on Ca handling in rat ventricular myocytes and assess its suitability as a specific inhibitor of SERCA. This was achieved by voltage clamp via perforated patch and [Ca(2+)]i measurement using Fluo-3 AM. TBQ produced a fully reversible, concentration dependent decrease in the rate of systolic Ca decay. 10µM TBQ decreased the amplitude of the systolic Ca transient by 48±5% and the rate of decay by 54±6%. SR Ca content was also reduced by 62±4%. However, 10µM TBQ also decreased the peak L-type Ca current by 23±7%. At higher concentrations (100µM), TBQ also activated an outward current with a current-voltage relationship consistent with a potassium current. This outward current was abolished by Glibenclamide (100µM). These data show that TBQ can be used to reversibly inhibit SERCA. However, at concentrations that decrease SERCA activity, TBQ also decreases the L-type Ca current and (at higher concentrations) activates an outward current which appears to be an ATP dependent potassium current. We conclude that TBQ cannot be used as a specific inhibitor of SERCA in rat ventricular myocytes.

Physiological and pathological modulation of ryanodine receptor function in cardiac muscle.

Calcium release from the sarcoplasmic reticulum (SR) in cardiac muscle occurs through a specialised release channel, the ryanodine receptor, RyR, via the process of Ca-induced Ca release (CICR). The open probability of the RyR is increased by elevation of cytoplasmic Ca concentration ([Ca(2+)](i)). However, in addition to Ca, other modulators affect the RyR open probability. Agents which increase the RyR opening during systole produce a transient increase of systolic [Ca(2+)](i) followed by a return to the initial level due to a compensating decrease of SR Ca content. Increasing RyR opening during diastole decreases SR Ca content and thereby decreases systolic [Ca(2+)](i). We therefore conclude that potentiation of RyR opening will, if anything, decrease systolic [Ca(2+)](i). The effects of specific examples of modulators of the RyR, such as phosphorylation, metabolic changes, heart failure and polyunsaturated fatty acids, are discussed.

Integrative analysis of calcium signalling in cardiac muscle.

This review discusses the control of the amplitude of the cardiac systolic Ca transient. The Ca transient arises largely from release from the sarcoplasmic reticulum (SR). Release is triggered by calcium-induced calcium release (CICR) whereby the entry of a small amount of Ca on the L-type Ca current, "the trigger", results in the release of much more Ca from the SR. There are three potential control points: (1) the Ca content of the SR; (2) the properties of the SR Ca release channel or ryanodine receptor (RyR); (3) the amplitude of the L-type Ca current. The data reviewed show that the Ca content of the SR has pronounced effects on systolic [Ca2+]i and, reciprocally, the amount of Ca released from the SR affects sarcolemmal Ca fluxes thereby "autoregulating" SR content. Modulation of the ryanodine receptor has no steady-state effect due to compensating changes of SR Ca content. An increase of the L-type Ca current results in an abrupt increase of systolic [Ca2+]i with little change of SR content. This is because of a coordinated increase of both the trigger and loading function of the Ca current. These results emphasise the importance of considering all aspects of Ca handling in the context of SR Ca release and thus the regulation of the systolic Ca transient and contraction in cardiac muscle.

Comparison of the effects of caffeine and other methylxanthines on [Ca2+]i in rat ventricular myocytes.

1. The effects of caffeine and other methylxanthines were investigated on intracellular calcium concentration ([Ca2+]i) and contraction in rat isolated ventricular myocytes. The use of the fluorescent indicator, Indo-1, allowed simultaneous measurement of [Ca2+]i and the intracellular concentration of the methylxanthines. 2. Rapid application of caffeine (10 mM) produced a transient rise of [Ca2+]i which decayed to resting levels. This was accompanied by a transient contraction which decayed to a level above baseline. The addition of theophylline also produced a transient increase of [Ca2+]i. However, following the initial transient, contraction decayed before redeveloping to a maintained level. 3. Direct measurements showed that [caffeine]i rose more quickly than did [theophylline]i. The slower rise of [theophylline]i was associated with a delay in the increase of [Ca2+]i. At lower concentrations of the methylxanthines, theophylline was less effective than caffeine at initiating Ca release. The rate of entry of theobromine was similar to that of theophylline. 4. Isocaffeine did not produce a rise of [Ca2+]i. The rate of rise of [isocaffeine]i was much slower than that of either caffeine or theophylline. 5. Measurements of the oil:water partition coefficient showed that the order of relative partitioning into oil was: caffeine > theophylline > theobromine > isocaffeine. This is similar to the order of rate of entry into the cell. 6. We conclude that many of the differences in the effects of these methylxanthines can be attributed to differences in membrane permeability due to differences in oil:water partition.

d-amphetamine increases choice of cigarette smoking over monetary reinforcement.

RATIONALE: Psychomotor stimulants previously have been found to increase the frequency of cigarette smoking, but it is unclear whether this is due to a non-specific increase in general activity or a specific increase in the reinforcing effects of smoking. OBJECTIVES: To investigate whether d-amphetamine increases the relative reinforcing effects of cigarette smoking. METHODS: Ninety minutes after d-amphetamine (7.5, 15 mg/70 kg) or placebo administration, 13 male and female subjects participated in 3-h sessions during which they could make a maximum of 20 choices between cigarette smoking (two puffs per choice), earning money ($0.25 per choice), or neither. In separate sessions, using the same subjects, the effects of d-amphetamine on the frequency of ad libitum smoking was assessed. RESULTS: During choice sessions, d-amphetamine dose-dependently increased smoking choices from 4.2 +/- 0.6 to 5.7 +/- 0.6. During sessions in which subjects smoked ad libitum, d-amphetamine increased number of cigarettes smoked from 2.8 +/- 0.4 to 3.8 +/- 0.6. Breath carbon monoxide (CO) levels, a measure of smoke exposure, showed corresponding dose-related increases. CONCLUSIONS: These results are consistent with previous findings that d-amphetamine increases smoking and provide evidence that this effect is due to a drug-produced increase in the relative reinforcing effects of cigarette smoking.

Effects of abstinence on cigarette smoking among outpatients with schizophrenia.

The authors of this study examined the effects of brief smoking abstinence on smoking among 6 individuals with schizophrenia or schizoaffective disorder. Before 6 of 12 experimental sessions, participants were required to provide breath carbon monoxide (CO) samples indicative of smoking abstinence; before the remaining sessions, participants provided CO samples indicating no abstinence. During sessions, participants obtained smoking opportunities (2 puffs/opportunity) under either fixed ratio-1 or progressive ratio (PR) schedules of reinforcement. Abstinence increased smoking under both schedules and increased breakpoint for smoking under the PR schedule. These data offer further evidence that smoking by individuals with schizophrenia is orderly, operant behavior that is modulated, at least in part, by variables that also affect smoking in people without major mental illness.