The clarion call for a third wave in medical education to optimise healthcare in the twenty-first century.

During the years preceding 1910, the education and training of physicians (doctors) -to-be was based mainly on a master-apprentice model; the primary focus then was on the teaching and development of clinical skills. In 1910, however, Abraham Flexner submitted a highly influential report to the American medical authorities: in it, he recommended that all medical schools should be university-based and that, importantly, medical practice should have a scientific basis strongly underpinned by the basic medical sciences. The recommendation provided the impetus for the design of medical education that begins with a pre-clinical phase to provide the strong scientific foundation for the clinical phase that follows. During the clinical phase, student learning will focus primarily on the clinical sciences relating to the diagnosis, treatment and management of patient care. Thus, two key 'pillars' (the basic sciences and the clinical sciences) of medical education were established; this two pillar model of medical education persisted for many decades thereafter and remained so till today. However, in order to optimise delivery of health care this must be viewed as an 'eco-system' taking into account the practice setting both present and future. The authors will attempt to provide a background to the changing trends in medical education and the changing practice environment, due primarily to the disruptive forces of change in this article.

Teaching of medical pharmacology: the need to nurture the early development of desired attitudes for safe and rational drug prescribing.

Pharmacology, as a basic medical science discipline, provides the scientific basis of therapeutics, i.e. the scientific foundation for safe and rational prescribing of drugs. The public, lay media, and the medical profession have raised serious concerns over the high incidence of errors of drug prescribing which compromise patient safety, including death of some patients, attributed mainly to inadequate teaching of medical pharmacology and, consequently, to medical graduates lacking skills in safe and effective drug prescribing. There is also overwhelming evidence that the pervasive and prevalent doctor-drug industry relationships have a strong influence over the prescribing habits and drug education of doctors. The British Pharmacological Society and American Association of Medical Colleges have crafted some insightful guidelines, including the learning of desired attitudes, for designing a medical pharmacology curriculum aimed at enhancing patient safety. This article will critically review the major issues relating to errors of drug prescribing, including the need to nurture the early development of desired attitudes which foster safe and rational drug prescribing. A simple educational approach, using a task analysis of drug prescribing, is applied to identify desired attitudes which should be incorporated into a basic pharmacology course for medical students in the twenty-first century.

Three-finger alpha-neurotoxins and the nicotinic acetylcholine receptor, forty years on.

The discovery, about forty years ago, of alpha-bungarotoxin, a three-finger alpha-neurotoxin from Bungarus multicinctus venom, enabled the isolation of the nicotinic acetylcholine receptor (nAChR), making it one of the most thoroughly characterized receptors today. Since then, the sites of interaction between alpha-neurotoxins and nAChRs have largely been delineated, revealing the remarkable plasticity of the three-finger toxin fold that has optimally evolved to utilize different combinations of functional groups to generate a panoply of target specificities to discern subtle differences between nAChR subtypes. New facets in toxinology have now broadened the scope for the use of alpha-neurotoxins in scientific discovery. For instance, the development of short, combinatorial library-derived, synthetic peptides that bind with sub-nanomolar affinity to alpha-bungarotoxin and prevent its interaction with muscle nAChRs has led to the in vivo neutralization of experimental alpha-bungarotoxin envenomation, while the successful introduction of pharmatopes bearing "alpha-bungarotoxin-sensitive sites" into toxin-insensitive nAChRs has permitted the use of various alpha-neurotoxin tags to localize and characterize new receptor subtypes. More ambitious strategies can now be envisaged for engineering rationally designed novel activities on three-finger toxin scaffolds to generate lead peptides of therapeutic value that target the nicotinic pharmacopoeia. This review details the progress made towards achieving this goal.

Characterization of the rat isolated retractor penis muscle as a model for the study of nitrergic transmission.

INTRODUCTION: The anococcygeus and retractor penis muscles are part of the erectile machinery in male rodents. The rat anococcygeus muscle is a widely used smooth muscle preparation for the study of the effects of test substances on adrenergic, nitrergic, and cholinergic transmission. There is, however, little information available on the process of autonomic transmission in the rat retractor penis muscle, although its autonomic innervation has generally been assumed to be similar to that of the anococcygeus muscle because of the contiguous nature of the two muscles. The present study investigated the involvement of nitrergic transmission in mediating relaxant responses of the rat retractor penis muscle to electrical field stimulation. METHODS: The retractor penis muscle was isolated from Sprague-Dawley rats and mounted in Krebs solution. Phentolamine (5 microM) was added to the bath to block the adrenergic responses of the muscle, which was then precontracted with carbachol (10 microM). RESULTS: Electrical field stimulation (20-30 V, 1 ms pulse width, at 0.5-20 Hz for 10 s) of the carbachol precontracted muscle elicited frequency-dependent relaxant responses (0.9-68%). Tetrodotoxin (1 microM), N(G)-nitro-L-arginine (L-NOARG) (50 microM), N(G)-nitro-L-arginine methylester (L-NAME) (100 microM), and haemoglobin (100 microM) inhibited these relaxant responses by 99.3%, 93.9%, 86.9%, and 77.5%, respectively. L-Arginine (250 microM) (but not its D-isomer) reversed the blockade produced by L-NOARG (72.7%) and L-NAME (81.5%). DISCUSSION: Our results provide clear evidence that the inhibitory (relaxant) responses of the rat retractor penis muscle to electrical field stimulation are mediated by nitric oxide involving the L-arginine-nitric oxide synthase-nitric oxide pathway. The rat retractor penis muscle is a versatile preparation that can replace the cumbersome preparations from the pig, ox, and horse, hitherto used as pharmacological models for the study of the retractor penis muscle.

Autonomic effects of some scorpion venoms and toxins.

1. The autonomic effects of venoms and toxins from several species of scorpions, including the Indian red scorpion Mesobuthus tamulus, the Chinese scorpion Buthus martensi Karsch and the Israeli scorpion Leiurus quinquestriatus quinquestriatus, all belonging to Buthidae, and the Asian black scorpions Heterometrus longimanus and Heterometrus spinifer, belonging to Scorpionidae, are reviewed. 2. The effects of the venoms of M. tamulus and L. q. quinquestriatus on noradrenergic and nitrergic transmission in the rat isolated anococcygeus muscle revealed that both venoms mediated their pharmacological effects via a prejunctional mechanism involving the activation of voltage-sensitive sodium channels with consequent release of neurotransmitters that mediate target organ responses, similar to the effects mediated by other alpha-scorpion toxins. 3. Two new toxins, Makatoxin I and Bukatoxin, were purified to homogeneity from the venom of B. martensi Karsch. Determination of their complete amino acid sequences confirmed that both toxins belonged to the class of alpha-scorpion toxins. The effects of both toxins on noradrenergic and nitrergic transmission in the rat anococcygeus muscle provided firm evidence that their pharmacological actions also closely resembled those mediated by other alpha-scorpion toxins on neuronal voltage-sensitive sodium channels. 4. The venoms of H. longimanus and H. spinifer were found to have high concentrations of noradrenaline (1.8 +/- 0.3 mmol/L) and relatively high concentrations of acetylcholine (79.8 +/- 1.7 micromol/L) together with noradrenaline (146.7 +/- 19.8 micromol/L), respectively, which can account for their potent direct cholinergic and noradrenergic agonist actions in the rat anococcygeus muscle. 5. Our studies confirmed that the rat anococcygeus muscle is an excellent nerve-smooth muscle preparation for investigating the effects of bioactive agents on noradrenergic and nitrergic transmission, as well as the direct agonist actions of these agents on post-synaptic alpha-adrenoceptors and M3 muscarinic cholinoceptors. Although many studies, including our own, have documented that scorpion venoms and toxins mediate their primary effects via a prejunctional mechanism that leads to the marked release of various autonomic neurotransmitters, our studies have shown that there are exceptions to this generally accepted phenomenon. In particular, we have provided firm evidence to show that the venoms from H. longimanus and H. spinifer do not have such a prejunctional site of action but, instead, the venoms mediate their autonomic effects through direct agonist actions on post-junctional muscarinic M3 cholinoceptors and alpha-adrenoceptors.

Candoxin, a novel toxin from Bungarus candidus, is a reversible antagonist of muscle (alphabetagammadelta ) but a poorly reversible antagonist of neuronal alpha 7 nicotinic acetylcholine receptors.

In contrast to most short and long chain curaremimetic neurotoxins that produce virtually irreversible neuromuscular blockade in isolated nerve-muscle preparations, candoxin, a novel three-finger toxin from the Malayan krait Bungarus candidus, produced postjunctional neuromuscular blockade that was readily and completely reversible. Nanomolar concentrations of candoxin (IC(50) = approximately 10 nm) also blocked acetylcholine-evoked currents in oocyte-expressed rat muscle (alphabetagammadelta) nicotinic acetylcholine receptors in a reversible manner. In contrast, it produced a poorly reversible block (IC(50) = approximately 50 nm) of rat neuronal alpha7 receptors, clearly showing diverse functional profiles for the two nicotinic receptor subsets. Interestingly, candoxin lacks the helix-like segment cyclized by the fifth disulfide bridge at the tip of the middle loop of long chain neurotoxins, reported to be critical for binding to alpha7 receptors. However, its solution NMR structure showed the presence of some functionally invariant residues involved in the interaction of both short and long chain neurotoxins to muscle (alphabetagammadelta) and long chain neurotoxins to alpha7 receptors. Candoxin is therefore a novel toxin that shares a common scaffold with long chain alpha-neurotoxins but possibly utilizes additional functional determinants that assist in recognizing neuronal alpha7 receptors.

Biochemical and pharmacological characterization of the venom of the black scorpion Heterometrus spinifer.

The sting of the black scorpion Heterometrus spinifer, which can cause intense localized pain, has not been reported to produce lethal cardiovascular complications, which are well known to result from scorpion envenomation as a consequence of a massive release of catecholamines. Therefore, we have undertaken a biochemical and pharmacological characterization of the venom of H. spinifer. Pharmacologically, the venom (0.125 microL/mL) produced a marked, reversible contracture in the chick biventer cervicis muscle that was blocked by d-tubocurarine (2 microM) but not by tetrodotoxin (5 microM) and omega-conotoxin GVIA (3 microM). The anticholinesterase neostigmine (1 microM) potentiated the contracture by 5.3-fold. An ultra-filtrate fraction of MW < 3000 (F3K) of the venom produced a similar contracture in the biventer muscle, whereas the retentate of MW > 3000 did not. In the rat anococcygeus muscle, the venom produced a contractile response that was partially (37.4 +/- 1.6%) blocked by atropine (5 microM); phentolamine (5 microM) blocked the remaining response. Tetrodotoxin (5 microM) did not block the contractile response of the venom on the anococcygeus muscle. Electrospray ionization-mass spectrometry/mass spectrometry confirmed the presence of high concentrations of acetylcholine (79.8 +/- 1.7 microM) and norepinephrine (146.7 +/- 19.8 microM) in H. spinifer venom, which can fully account for the observed cholinergic and adrenergic effects. In contrast to scorpion venoms that selectively target neuronal ion channels in mediating transmitter release, our data show that H. spinifer venom does not possess such activity, which likely explains the apparent lack of lethality of black scorpion envenomation.