A progressive assessment strategy improves student learning and perceived course quality in undergraduate physiology.

In 2010, second-year physiology (n = 165) had a traditional single 3-h end-of-semester exam. To provide diagnostic feedback earlier, for students enrolled in 2011 (n = 128), we incorporated an in-class exam at 3 wk in addition to the final exam. Based on initial analysis and positive student comments, for the 2012 cohort (n = 148), we expanded this to incorporate four 1-h in-class exams every 3 wk plus a short final integrative exam. Average scores from exams and questionnaires (student evaluations of learning and teaching, 10 questions) were compared among 2010, 2011, and 2012 cohorts. We also compared scores in the practical component of the course, which had a constant format for all cohorts. Data are given as means ± SD; statistical analyses were done with unpaired two-way Students t-tests. From 2010 to 2012, there was a significant improvement in total exam scores (59.7 ± 15.8 vs. 68.6 ± 14.2, P < 0.001) but no significant change in total practical scores (72.3 ± 9.0 vs. 74.4 ± 10.2, P = 0.05), indicating that the rise in exam score was not due to higher academic abilities of the 2012 cohort. Overall mean student evaluation of learning and teaching responses (4.9 ± 0.4 vs. 5.3 ± 0.3, P = 0.015) and overall percent broad agreement (66.0 ± 8.0 vs. 79.2 ± 7.5, P = 0.003) indicated a significant improvement in student satisfaction. In conclusion, both learning outcome and perceived course quality were enhanced by the increased frequency of examinations, possibly by promoting consistent student study habits.

The antiarrhythmic actions of bisaramil and penticainide result from mixed cardiac ion channel blockade.

Decades of focus on selective ion channel blockade has been dismissed as an effective approach to antiarrhythmic drug development. In that context many older antiarrhythmic drugs lacking ion channel selectivity may serve as tools to explore mixed ion channel blockade producing antiarrhythmic activity. This study investigated the non-clinical electrophysiological and antiarrhythmic actions of bisaramil and penticainide using in vitro and in vivo methods. In isolated cardiac myocytes both drugs directly block sodium currents with IC50 values of 13µM (bisaramil) and 60µM (penticainide). Both drugs reduced heart rate but prolonged the P-R, QRS and Q-T intervals of the ECG (due to sodium and potassium channel blockade) in intact rats. They reduced cardiac conduction velocity in isolated rat hearts, increased the threshold currents for capture and fibrillation (indices of sodium channel blockade) and reduced the maximum following frequency as well as prolonged the effective refractory period (indices of potassium channel blockade) of electrically stimulated rat hearts. Both drugs reduced ventricular arrhythmias and eliminated mortality due to VF in ischemic rat hearts. The index of cardiac electrophysiological balance (iCEB) did not change significantly over the dose range evaluated; however, different drug effects resulted when changes in BP and HR were considered. While bisaramil is a more potent sodium channel blocker compared to penticainide, both produce a spectrum of activity against ventricular arrhythmias due to mixed cardiac ion channel blockade. Antiarrhythmic drugs exhibiting mixed ion channel blockade may serve as tools for development of safer mixed ion channel blocking antiarrhythmic drugs.

The cardiac persistent sodium current: an appealing therapeutic target?

The sodium current in the heart is not a single current with a mono-exponential decay but rather a mixture of currents with different kinetics. It is not clear whether these arise from distinct populations of channels, or from modulation of a single population. A very slowly inactivating component, [(INa(P))] I(Na(P)) is usually about 1% of the size of the peak transient current [I(Na(T))], but is enhanced by hypoxia. It contributes to Na(+) loading and cellular damage in ischaemia and re-perfusion, and perhaps to ischaemic arrhythmias. Class I antiarrhythmic agents such as flecainide, lidocaine and mexiletine generally block I(NA(P)) more potently than block of I(Na(T)) and have been used clinically to treat LQT3 syndrome, which arises because mutations in SCN5A produce defective inactivation of the cardiac sodium channel. The same approach may be useful in some pathological situations, such as ischaemic arrhythmias or diastolic dysfunction, and newer agents are being developed with this goal. For example, ranolazine blocks I(Na(P)) about 10 times more potently than I(Na(T)) and has shown promise in the treatment of angina. Alternatively, the combination of I(Na(P)) block with K(+) channel block may provide protection from the induction of Torsades de Pointe when these agents are used to treat atrial arrhythmias (eg Vernakalant). In all of these scenarios, an understanding of the role of I(Na(P)) in cardiac pathophysiology, the mechanisms by which it may affect cardiac electrophysiology and the potential side effects of blocking I(Na(P)) in the heart and elsewhere will become increasingly important.

Pharmacological and toxicological activity of RSD921, a novel sodium channel blocker.

BACKGROUND: RSD921, the R,R enantiomer of the kappa (k) agonist PD117,302, lacks significant activity on opioid receptors. METHODS: The pharmacological and toxicological actions were studied with reference to cardiovascular, cardiac, antiarrhythmic, toxic and local anaesthetic activity. RESULTS: In rats, dogs and baboons, RSD921 dose-dependently reduced blood pressure and heart rate. In a manner consistent with sodium channel blockade it prolonged the PR and QRS intervals of the ECG. Furthermore, in rats and NHP, RSD921 increased the threshold currents for induction of extra-systoles and ventricular fibrillation (VFt), and prolonged effective refractory period (ERP). In rats, RSD921 was protective against arrhythmias induced by electrical stimulation and coronary artery occlusion. Application of RSD921 to voltage-clamped rat cardiac myocytes blocked sodium currents. RSD921 also blocked transient (ito) and sustained (IKsus) outward potassium currents, albeit with reduced potency relative to sodium current blockade. Sodium channel blockade due to RSD921 in myocytes and isolated hearts was enhanced under ischaemic conditions (low pH and high extracellular potassium concentration). When tested on the cardiac, neuronal and skeletal muscle forms of sodium channels expressed in Xenopus laevis oocytes, RSD921 produced equipotent tonic block of sodium currents, enhanced channel block at reduced pH (6.4) and marked use-dependent block of the cardiac isoform. RSD921 had limited but quantifiable effects in subacute toxicology studies in rats and dogs. Pharmacokinetic analyses were performed in baboons. Plasma concentrations producing cardiac actions in vivo after intravenous administration of RSD921 were similar to the concentrations effective in the in vitro assays utilized. CONCLUSIONS: RSD921 primarily blocks sodium currents, and possesses antiarrhythmic and local anaesthetic activity.

Spontaneous intrauterine growth restriction due to increased litter size in the guinea pig programmes postnatal growth, appetite and adult body composition.

Intrauterine growth restriction (IUGR) and subsequent neonatal catch-up growth are implicated in the programming of increased appetite, adiposity and cardiometabolic diseases. Guinea pigs provide an alternate small animal model to rodents to investigate mechanisms underlying prenatal programming, being relatively precocial at birth, with smaller litter sizes and undergoing neonatal catch-up growth after IUGR. The current study, therefore, investigated postnatal consequences of spontaneous IUGR due to varying litter size in this species. Size at birth, neonatal, juvenile (post-weaning, 30-60 days) and adolescent (60-90 days) growth, juvenile and adolescent food intake, and body composition of young adults (120 days) were measured in 158 male and female guinea pigs from litter sizes of one to five pups. Compared with singleton pups, birth weight of pups from litters of five was reduced by 38%. Other birth size measures were reduced to lesser degrees with head dimensions being relatively conserved. Pups from larger litters had faster fractional neonatal growth and faster absolute and fractional juvenile growth rates (P<0.005 for all). Relationships of post-weaning growth, feed intakes and adult body composition with size at birth and neonatal growth rate were sex specific, with neonatal growth rates strongly and positively correlated with adiposity in males only. In conclusion, spontaneous IUGR due to large litter sizes in the guinea pig causes many of the programmed sequelae of IUGR reported in other species, including human. This may therefore be a useful model to investigate the mechanisms underpinning perinatal programming of hyperphagia, obesity and longer-term metabolic consequences.

An analysis of cardiac sodium channel properties using digital signal processing techniques.

The properties of single sodium channels in membrane patches from isolated rat ventricular myocytes were analyzed. Both cell-attached and inside-out patch configurations were examined. A digital signal processing method was used which allowed accurate determination of single-channel conductance and mean open time, even in situations where many channels coexisted in the patch. The results show that the cardiac sodium channel has a conductance of 5.3 pS at room temperature, and shows no rectification or saturation in the physiological ranges of ion concentration and membrane potential. The active channels contained in the membrane patch opened and closed independently of each other. A transition probability matrix, which describes transitions between all current levels, can also be generated, analysis of which permits an estimate of individual mean channel open time as well as the degree of coupling between channels.

Amitriptyline pharmacologically preconditions rat hearts against cardiac ischemic-reperfusion injury.

BACKGROUND/OBJECTIVES: Amitriptyline (AMY) is a tricyclic anti-depressant that has recently been shown to have anti-inflammatory properties. We investigated whether AMY is cardioprotective against reperfusion injury in ex-vivo rat hearts. METHODS: Thirty adult Sprague-Dawley rat hearts were perfused ex-vivo in a Langendorff apparatus. All hearts except SHAM (n = 6, perfused for 110 min.) received 30 min no-flow ischemia followed by 40 min reperfusion (I-R). One group (n = 6) was untreated before I-R (non-preconditioned; NPC), another non-preconditioned group was perfused with 10 µM amitriptyline for 30 min before I-R (NPC-AMY, n = 6). One group was preconditioned with 3 × 5-minute periods of ischemia before I-R (PC, n = 6) and a fifth group was preconditioned in the presence of 10 µM amitriptyline (PC-AMY, n = 6). p38 phosphorylation and HMGB1 levels were quantified using Western blots. Data was analysed using multiway ANOVAs with Tukey HSD and linear regression models with Sobel mediator tests. RESULTS: NPC hearts recovered poorly (LVDP recovered to 26.5 ± 10.5% of pre-ischemic values, compared to PC hearts (82.8 ± 14.9%: P < 0.05)). PC-AMY (69.9 ± 6.16%) and NPC-AMY (90.3 ± 10.0%) groups both recovered well (P < 0.05). The Sobel mediator test suggested that p38 activity may be indirectly involved in the amitriptyline induced cardioprotection (P < 0.05). HMGB1 was lower in amitriptyline treated hearts compared to the non-preconditioned hearts (P < 0.05) but the multiway ANOVA test suggests that HMGB1 was not involved in amitriptyline induced protection. CONCLUSIONS: Amitriptyline at 10 µM protects hearts against ischemic-reperfusion injury which may be partially mediated through p38 phosphorylation.

The relation between transmitter release and Ca2+ entry at the mouse motor nerve terminal: role of stochastic factors causing heterogeneity.

The relation between quantal transmitter release and presynaptic Ca2+/Ba2+ entry at the mouse neuromuscular junction was studied, making use of the finding that in the presence of Ba2+ trains of nerve stimuli or brief nerve terminal depolarizations elicit "tails" of raised miniature end-plate potential frequency (fm) that reflect entry of Ba2+ per pulse, and hence effectiveness of pulses in opening Ca2+/Ba2+ channels; at the same time these pulses elicit end-plate potentials. With nerve stimulation in the presence of Ba2+ and Ca2+ and modulation of release by raised Mg2+ or bekanamycin, slopes of log quantal content (m) vs log apparent Ba2+ entry per pulse were close to 4, which is the same as the Hill coefficient for Ba2+ cooperativity derived from other data. With depolarizing pulses of varied intensity, however, similar plots gave slopes close to 2, with Ba2+ alone or in a mixture of Ca2+ and Ba2+. Thus, the relation between transmitter release and Ca2+ (or Ba2+) entry apparently depends upon how entry is varied; varying the numbers of channels opened is not the same as varying ion entry per channel. A mathematical model was developed to examine the consequences of heterogeneity of local Ca2+ (or Ba2+) between release sites, arising because of stochastic variation of number and time course of Ca2+ channels opened per site; the experimental results were consistent with this model. It was therefore concluded that release is normally governed by intracellular Ca2+ close to points of Ca2+ entry through channels; stochastic factors give rise to more release than if Ca2+ were homogeneously distributed. If Ca2+ channels are uniformly close to release sites the average number of channels opened per site per action potential may be as low as 4.

Inactivation-resistant channels underlying the persistent sodium current in rat ventricular myocytes.

Single-channel sodium currents that could be blocked with TTX were elicited by depolarizing voltage pulses in either cell-attached or inside-out patches from rat ventricular myocytes. A transient burst of channels was followed by late-opening (persistent) channels with low open probability. Conditioning depolarizing pre-pulses that inactivated transient channels and 'chattering' late-opening channels had no effect on persistent channels. The open probability of persistent channels reached a maximum at more negative potentials than transient channels. Between -70 mV and -40 mV, the average open time of persistent channels increased, whereas the average open time of transient channels did not change significantly, so the open times of the two channels diverged as the potential became more positive. The conductance of transient and persistent channels was similar, and the conductance of both kinds of channel increased at more depolarized potentials.

The effect of aliphatic alcohols on the transient potassium current in hippocampal neurones.

1. The transient potassium current was recorded in single hippocampal CA1 neurones from the rat by use of the whole-cell patch clamp technique. The effects on this current of a homologous series of aliphatic alcohols, ranging from butanol to octanol, were investigated. 2. The predominant effect of octanol (and the other alcohols) was to cause an increase in the initial rate of decay of the transient potassium current together with a slight decrease in the rate of decay of later phases of the current, such that the current decay became markedly non-monotonic. The alcohols also caused a decrease in peak current amplitude which could not be accounted for solely by the change in current decay kinetics. 3. The effect of the alcohols was concentration-dependent and readily reversible. Increasing chain length increased the potency of each alcohol by about 3 fold for each methylene group added. Other than a difference in potency, there appeared to be little difference in the action of aliphatic alcohols of different chain length on the transient current. 4. The alcohols did not appreciably change the voltage-dependence of steady state inactivation or activation of the transient potassium current. 5. The rate of inactivation of the transient current in these cells was only weakly voltage-dependent. This weak voltage-dependence was not changed by the presence of aliphatic alcohols, neither was the effect of the alcohols themselves voltage-dependent. 6. The potencies of each of the aliphatic alcohols were well correlated with their respective membrane/buffer partition coefficients, a finding which implies a hydrophobic locus of action.

The effects of propofol on macroscopic and single channel sodium currents in rat ventricular myocytes.

1. The effects of the injectable anaesthetic agent propofol (di-isopropyl phenol) were examined on sodium currents and single sodium channels by use of patch-clamp techniques in ventricular myocytes isolated from rat hearts. 2. Propofol dose-dependently blocked the whole cell sodium currents evoked by a voltage step to -30 mV from a holding potential of -90 mV with an EC50 of 14.8+/-2.3 microM (mean+/-s.e.mean). 3. Propofol caused a substantial hyperpolarizing shift in the voltage-dependence of inactivation of sodium currents (168 microM (30 microg ml(-1)) propofol caused a -14 mV shift (P<0.01); 56 microM caused a -8 mV shift (P<0.05)). A smaller shift in the voltage-dependence of activation was produced (4 mV by 168 microM (not statistically significant)), but this was to more depolarized potentials. The maximal sodium conductance, as judged from the activation and inactivation curves, was reduced by 13% by 168 microM propofol (not statistically significant), but propofol did not affect the reversal potential of the current-voltage relationship. 4. The macroscopic rate of inactivation, as measured by the time constant of the exponential fall of current amplitude from the peak current, was also slowed by propofol, from a control time constant of 1.78+/-0.31 ms to 2.93+/-0.47 ms (mean+/-s.e.mean, n=8, P<0.05) by 168 microM propofol. Despite the increase in the time constant, the macroscopic inactivation remained well fitted by a single exponential. The macroscopic rate of activation was also slowed, but to a lesser degree (<10%, not statistically significant) by 168 microM propofol. 5. Propofol slowed the rate of recovery from inactivation of the sodium current, as measured by a two pulse protocol. Propofol (168 microM) increased the time constant of recovery, measured at -100 mV and room temperature, from a control value of 55+/-5.9 ms to 141+/-24.2 ms (mean+/-s.e.mean, n=8, P<0.01). Although the time constant was increased at all voltages measured, the intrinsic voltage-dependence of the rate of recovery was not changed. 6. Single channel recordings showed that the mean open time of single sodium channels was dramatically reduced by propofol (from 0.50+/-0.02 ms in control to 0.28+/-0.01 ms by 56 +/-M propofol and to 0.24+/-0.01 ms by 168 microM, both significantly different from control, P<0.01). Single channel conductance was not changed by either concentration of propofol.

Tonic and use-dependent block of sodium currents in isolated cardiac myocytes by bisaramil.

1. The effects of bisaramil on sodium currents in rat isolated cardiac myocytes were examined by use of tight-seal, whole-cell patch clamp techniques. Bisaramil produced a concentration-dependent, readily reversible reduction in peak transient sodium current. When the sodium current was evoked at 3 s intervals the estimated ED50 for bisaramil was about 11 microM. 2. Bisaramil (16 microM) produced a shift in the inactivation curve to hyperpolarized potentials of about 10 mV, but produced no change in the voltage-dependence of activation. 3. The block of the sodium current by bisaramil showed a profound use-dependence. A concentration of 10 microM produced a considerable block of the current with repeated stimulation. The recovery from block was biphasic, showing fast and slow components which had time constants of about 40 ms and 5 s respectively. 4. Bisaramil produced little tonic block of the sodium current at concentrations of 100 microM; at 300 microM it produced tonic block of around 50%, with extreme use-dependence. 5. Bisaramil appeared not to interact primarily with the inactivated form of the channel, since lengthening the depolarizing pulses did not affect the degree of block produced.

Modification of motor nerve terminal excitability by alkanols and volatile anaesthetics.

A method of local polarization-excitation was used to study changes in motor nerve terminal excitability produced by n-alkanols and volatile anaesthetics in mouse diaphragm preparations. Ethanol and propanol caused an exaggeration of 'accommodation', i.e., the increase in excitation threshold produced by a conditioning depolarization. Butanol, hexanol and octanol had mixed effects, producing a rise in the minimum threshold (threshold after removal of resting accommodation) in addition to an increase in accommodation. Volatile anaesthetics produced effects on excitability at concentrations comparable to minimum alveolar concentration. The action of enflurane was essentially only to increase accommodation while methoxyflurane produced an increase in threshold insensitive to conditioning polarization. Halothane and isoflurane produced intermediate effects. Accommodation curves were little affected by Ba2+ or 4-aminopyridine and were consistent with accommodation being a reflection of inactivation of the Na+ current system. We conclude that volatile anaesthetics, at concentrations comparable to those producing anaesthesia, may substantially modify Na+ channel gating and inactivation.

Effects of lignocaine and quinidine on the persistent sodium current in rat ventricular myocytes.

1. The effects of the Class 1 antiarrhythmic agents lignocaine and quinidine on action potentials, and on sodium currents and potassium currents activated by depolarization, were examined in rat isolated ventricular myocytes by the whole cell, tight seal recording technique. 2. Tetrodotoxin and lignocaine shortened, whereas quinidine prolonged, the duration of the plateau phase of action potentials. 3. At low concentrations, lignocaine and quinidine blocked a persistent sodium current that was resistant to inactivation but they had only a small effect on the transient sodium current. At higher concentrations, they also blocked the transient sodium current. 4. Quinidine, but not tetrodotoxin or lignocaine, depressed potassium currents activated by depolarization and this could account for the prolongation of the plateau phase caused by quinidine. 5. It is suggested that block of the persistent sodium current may be responsible, at least in part, for the antiarrhythmic action of lignocaine and quinidine.

Effects of butanedione monoxime on neuromuscular transmission.

1. The amplitude of endplate potentials was increased by concentrations of butanedione monoxime (BDM, 5-20 mM) that typically caused muscle paralysis. 2. Although BDM slowed the decay of spontaneous miniature endplate currents, the effect was insufficient to explain most of the large increase in amplitude of endplate potentials. 3. The quantal content of endplate potentials was increased by BDM in a reversible, concentration-dependent manner. 4. The frequency of miniature endplate potentials was not changed by 10 mM BDM in the presence of normal or raised potassium concentrations, indicating that BDM does not change quantal content by a direct effect on calcium channels or on steady-state intracellular calcium concentration. 5. A change in the time course of the extracellularly recorded nerve terminal action potential caused by BDM was similar to the change produced by 4-aminopyridine (4-AP). 6. The increase in quantal content produced by BDM was only slightly reduced in the presence of 1 mM tetraethylammonium (TEA) but was significantly reduced in the presence of 0.5 to 1 mM 4-AP. 7. It was concluded that BDM blocks a 4-AP-sensitive potassium conductance in motor nerve terminals and, by increasing the duration of the action potential in this way, increases evoked transmitter release.

Electrophysiological and antiarrhythmic actions of the kappa agonist PD 129290, and its R,R (+)-enantiomer, PD 129289.

1. The S,S (-)-enantiomer PD 129290, a kappa agonist, and its corresponding inactive R,R (+)-enantiomer (PD 129289) were studied in rat isolated hearts and in intact rats for cardiovascular and antiarrhythmic actions. The electrophysiological actions of PD 129290 were also studied in rat isolated cardiac myocytes using voltage clamp. 2. Ventricular pressure, heart rate and ECG were studied in isolated hearts while blood pressure, heart rate and ECG were studied in pentobarbitone-anaesthetized rats. In the latter, responses to electrical stimulation and coronary occlusion were also investigated. 3. In isolated hearts both enantiomers, over the concentration range 2-16 microM, dose-dependently reduced systolic ventricular pressure and heart rate while prolonging the P-R and QRS intervals of the ECG. 4. At doses of 1-32 mumol kg-1 both enantiomers reduced blood pressure and heart rate in anaesthetized rats. In addition, both enantiomers increased the size of the RSh and increased P-R, QRS, and Q-T intervals of the ECG. The thresholds for premature beats and ventricular fibrillation were dose-dependently increased by PD 129289. At lower doses PD 129290 decreased thresholds. These decreases were blocked by naloxone to reveal underlying increases similar to those seen with PD 129289. Both enantiomers increased refractory periods. 5. Naloxone (8 mumol kg-1) did not alter any of the actions of PD 129290, except to abolish the initial decreases in thresholds in intact rats seen with lower doses of PD 129290. 6. Both enantiomers (2 and 8 mumol kg-1) equally reduced arrhythmias in anaesthetized rats subject to occlusion of a coronary artery. 7. In rat isolated cardiac myocytes 20 microM PD 129290, in the presence and absence of naloxone decreased the amplitude of the transient sodium current by about 50% without affecting the voltage dependence of activation or inactivation of this current.8. The antiarrhythmic actions of both enantiomers appear to primarily result from their Class I(sodium channel blockade) properties which are independent of kappa agonism.

Modulation of the transient potassium current in rat hippocampal neurones by cholecystokinin.

Cholecystokinin (CCK) affects neuronal excitability in a variety of in vivo and in vitro preparations, apparently by modulating a resting potassium conductance. The data presented here show that CCK (applied as CCK8-S) also affects the transient potassium current in hippocampal neurones, by changing the voltage dependence of the inactivation and activation of the current. The way in which the voltage dependence is changed can lead to either an enhancement of the current or an attenuation, depending upon the voltage protocol used. This effect of CCK does not desensitise over a time period of minutes, and may therefore be important in controlling neuronal excitability in the CNS.

An electrophysiological basis for the antiarrhythmic actions of the kappa-opioid receptor agonist U-50,488H.

This study examined the actions of the selective kappa-opioid receptor agonist, U-50,488H, on voltage activated Na+ and K+ currents in isolated rat cardiac myocytes. U-50,488H produced a concentration-dependent block of the transient Na+ current with an ED50 of about 15 microM, and, at higher concentrations (40-50 microM), a block of the plateau K+ current and an increase in the rate of decay of the transient K+ current. In addition U-50,488H produced a hyperpolarising shift in the inactivation curve for the transient Na+ current without altering the voltage dependence for activation and without an effect on the voltage dependence of inactivation or activation of K+ currents. The block of Na+ currents by U-50,488H showed pronounced use dependence. The kappa-opioid receptor antagonist MR2266 did not itself produce any change in the Na+ or K+ currents and did not change the channel blocking properties of U-50,488H. Thus, since the antiarrhythmic actions of U-50,488H are not blocked by MR2266 or naloxone, the effects of U-50,488H to block Na+ and K+ currents are the most likely reasons for its antiarrhythmic actions, rather than an action at kappa-opioid receptors.

The cardiac electrophysiological effects of sparteine and its analogue BRB-I-28 in the rat.

This study compares the cardiovascular and antiarrhythmic effects of sparteine and a 3,7-diheterobicyclo[3.3.1]nonane analogue of sparteine, BRB-I-28, in pentobarbitone-anaesthetized rats subjected to left-ventricle electrical stimulation and occlusion of the left anterior descending coronary artery. Sparteine and BRB-I-28 produced a dose-dependent reduction in heart rate and blood pressure over the dose range 1-64 mumol/kg/min. As well, the P-R and Q-aT intervals of the electrocardiogram (ECG) were prolonged. The thresholds for induction of premature beats and ventricular fibrillation were dose-dependently increased and both drugs increased refractoriness. While sparteine and BRB-I-28 (at 16 and 64 mumol/kg/min, respectively) did not change the incidence of premature beats or ventricular tachycardia with coronary occlusion, both drugs equally reduced the incidence of ventricular fibrillation. We characterized the actions of sparteine and BRB-I-28 on cardiac Na+, transient outward and sustained outward plateau K+ currents of rat myocytes using the whole-cell patch-clamp. Sparteine and BRB-I-28 produced a concentration-dependent reduction in Na+ current with EC50 values of 110 and 230 microM, respectively. Both drugs produced hyperpolarizing shifts of 8 and 11 mV, respectively, for Na+ channel inactivation while neither produced a change in channel activation. Both drugs produced a concentration-dependent block of the sustained plateau K+ current and increased the rate of decay of the transient outward K+ current. Thus, sparteine and BRB-I-28 possess Na+ and K+ channel blocking properties which may account for their antiarrhythmic actions against electrical and ischaemic arrhythmias.

Cholecystokinin modulates voltage dependent K+ currents in cultured rat hippocampal neurones.

Much interest has been focussed recently on neuroactive peptides originally found in the peripheral nervous system, but now, increasingly, being shown to be present in considerable amounts in the mammalian CNS. One of these peptides, cholecystokinin (CCK), is present in large amounts in higher brain areas. Immunoreactivity to CCK has been demonstrated in the mammalian hippocampus and dentate gyrus, localised in nerve terminals, and increasingly this peptide is being suggested as having a role as a transmitter in the CNS. Generally, CCK appears to produce depolarisations of neurones: e.g. mesenteric ganglion cells, and hippocampal neurones [5], although the mechanism by which it does so remains unclear, there being reports of either a decrease in input resistance, an increase, or both.