TRPM4 links calcium signaling to membrane potential in pancreatic acinar cells.

Transient receptor potential cation channel subfamily M member 4 (TRPM4) is a Ca2+-activated nonselective cation channel that mediates membrane depolarization. Although, a current with the hallmarks of a TRPM4-mediated current has been previously reported in pancreatic acinar cells (PACs), the role of TRPM4 in the regulation of acinar cell function has not yet been explored. In the present study, we identify this TRPM4 current and describe its role in context of Ca2+ signaling of PACs using pharmacological tools and TRPM4-deficient mice. We found a significant Ca2+-activated cation current in PACs that was sensitive to the TRPM4 inhibitors 9-phenanthrol and 4-chloro-2-[[2-(2-chlorophenoxy)acetyl]amino]benzoic acid (CBA). We demonstrated that the CBA-sensitive current was responsible for a Ca2+-dependent depolarization of PACs from a resting membrane potential of -44.4 ± 2.9 to -27.7 ± 3 mV. Furthermore, we showed that Ca2+ influx was higher in the TRPM4 KO- and CBA-treated PACs than in control cells. As hormone-induced repetitive Ca2+ transients partially rely on Ca2+ influx in PACs, the role of TRPM4 was also assessed on Ca2+ oscillations elicited by physiologically relevant concentrations of the cholecystokinin analog cerulein. These data show that the amplitude of Ca2+ signals was significantly higher in TRPM4 KO than in control PACs. Our results suggest that PACs are depolarized by TRPM4 currents to an extent that results in a significant reduction of the inward driving force for Ca2+. In conclusion, TRPM4 links intracellular Ca2+ signaling to membrane potential as a negative feedback regulator of Ca2+ entry in PACs.

Transient receptor potential channels and itch: how deep should we scratch?

Over the past 30 years, transient receptor potential (TRP) channels have evolved from a somewhat obscure observation on how fruit flies detect light to become the center of drug discovery efforts, triggering a heated debate about their potential as targets for therapeutic applications in humans. In this review, we describe our current understanding of the diverse mechanism of action of TRP channels in the itch pathway from the skin to the brain with focus on the peripheral detection of stimuli that elicit the desire to scratch and spinal itch processing and sensitization. We predict that the compelling basic research findings on TRP channels and pruritus will be translated into the development of novel, clinically useful itch medications.

Endocannabinoids limit excessive mast cell maturation and activation in human skin.

BACKGROUND: Mast cells (MCs) crucially contribute to many inflammatory diseases. However, the physiological controls preventing excessive activities of MCs in human skin are incompletely understood. OBJECTIVE: Since endocannabinoids are important neuroendocrine MC modifiers, we investigated how stimulation/inhibition of cannabinoid 1 (CB1) receptors affect the biology of human skin MCs in situ. METHODS: This was investigated in the MC-rich connective tissue sheath of organ-cultured human scalp hair follicles by quantitative (immuno)histomorphometry, ultrastructural, and quantitative PCR techniques with the use of CB1 agonists or antagonists, CB1 knockdown, or CB1 knockout mice. RESULTS: Kit+ MCs within the connective tissue sheath of human hair follicles express functional CB1 receptors, whose pharmacological blockade or gene silencing significantly stimulated both the degranulation and the maturation of MCs from resident progenitor cells in situ (ie, enhanced the number of tryptase+, FcεRIα, or chymase+ connective tissue sheath-MCs). This was, at least in part, stem cell factor-dependent. CB1 agonists counteracted the MC-activating effects of classical MC secretagogues. Similar phenomena were observed in CB1 knockout mice, attesting to the in vivo relevance of this novel MC-inhibitory mechanism. CONCLUSION: By using human hair follicle organ culture as an unconventional, but clinically relevant model system for studying the biology of MCs in situ, we show that normal skin MCs are tightly controlled by the endocannabinoid system. This limits excessive activation and maturation of MCs from resident progenitors via "tonic" CB1 stimulation by locally synthesized endocannabinoids. The excessive numbers and activation of MCs in allergic and other chronic inflammatory skin diseases may partially arise from resident intracutaneous MC progenitors, for example, because of insufficient CB1 stimulation. Therefore, CB1 stimulation is a promising strategy for the future management of allergy and MC-dependent skin diseases.

Laparoscopic cholecystectomy after a quarter century: why do we still convert?

BACKGROUND: Laparoscopic cholecystectomy (LC) is the gold standard procedure for gallbladder removal. However, conversion to open surgery is sometimes needed. The factors underlying a surgeon's decision to convert a laparoscopic case to an open case are complex and poorly understood. With decreasing experience in open cholecystectomy, this procedure is however no longer the "safe" alternative it once was. With such an impending paradigm shift, this study aimed to identify the main reasons for conversion and ultimately to develop guidelines to help reduce the conversion rates. METHODS: Using the National Surgical Quality Improvement Program (NSQIP) database and financial records, the authors retrospectively reviewed 1,193 cholecystectomies performed at their institution from 2002 to 2009 and identified 70 conversions. Two independent surgeons reviewed the operative notes and determined the reasons for conversion. The number of ports at the time and the extent of dissection before conversion were assessed and used to create new conversion categories. Hospital length of stay (LOS), 30-day complications, operative times and charges, and hospital charges were compared between the new groups. RESULTS: In 91% of conversion cases, the conversion was elective. In 49% of these conversions, the number of ports was fewer than four. According to the new conversion categories, most conversions were performed after minimal or no attempt at dissection. There were no differences in LOS, complications, operating room charges, or hospital charges between categories. Of the six emergent conversions (9%), bleeding and concern about common bile duct (CBD) injury were the main reasons. One CBD injury occurred. CONCLUSIONS: In 49% of the cases, conversion was performed without a genuine attempt at laparoscopic dissection. Considering this new insight into the circumstances of conversion, the authors recommend that surgeons make a genuine effort at a laparoscopic approach, as reflected by placing four ports and trying to elevate the gallbladder before converting a case to an open approach.

"Sebocytes' makeup": novel mechanisms and concepts in the physiology of the human sebaceous glands.

The pilosebaceous unit of the human skin consists of the hair follicle and the sebaceous gland. Within this "mini-organ", the sebaceous gland has been neglected by the researchers of the field for several decades. Actually, it was labeled as a reminiscence of human development ("a living fossil with a past but no future"), and was thought to solely act as a producer of sebum, a lipid-enriched oily substance which protects our skin (and hence the body) against various insults. However, due to emerging research activities of the past two decades, it has now become evident that the sebaceous gland is not only a "passive" cutaneous "relic" to establish the physico-chemical barrier function of the skin against constant environmental challenges, but it rather functions as an "active" neuro-immuno-endocrine cutaneous organ. This review summarizes recent findings of sebaceous gland research by mainly focusing on newly discovered physiological functions, novel regulatory mechanisms, key events in the pathology of the gland, and future directions in both experimental and clinical dermatology.

Prolactin--a novel neuroendocrine regulator of human keratin expression in situ.

The controls of human keratin expression in situ remain to be fully elucidated. Here, we have investigated the effects of the neurohormone prolactin (PRL) on keratin expression in a physiologically and clinically relevant test system: organ-cultured normal human hair follicles (HFs). Not only do HFs express a wide range of keratins, but they are also a source and target of PRL. Microarray analysis revealed that PRL differentially regulated a defined subset of keratins and keratin-associated proteins. Quantitative immunohistomorphometry and quantitative PCR confirmed that PRL up-regulated expression of keratins K5 and K14 and the epithelial stem cell-associated keratins K15 and K19 in organ-cultured HFs and/or isolated HF keratinocytes. PRL also up-regulated K15 promoter activity and K15 protein expression in situ, whereas it inhibited K6 and K31 expression. These regulatory effects were reversed by a pure competitive PRL receptor antagonist. Antagonist alone also modulated keratin expression, suggesting that "tonic stimulation" by endogenous PRL is required for normal expression levels of selected keratins. Therefore, our study identifies PRL as a major, clinically relevant, novel neuroendocrine regulator of both human keratin expression and human epithelial stem cell biology in situ.

Evaluation of colonoscopy technical skill levels by use of an objective kinematic-based system.

BACKGROUND: Colonoscopy requires training and experience to ensure accuracy and safety. Currently, no objective, validated process exists to determine when an endoscopist has attained technical competence. Kinematics data describing movements of laparoscopic instruments have been used in surgical skill assessment to define expert surgical technique. We have developed a novel system to record kinematics data during colonoscopy and quantitatively assess colonoscopist performance. OBJECTIVE: To use kinematic analysis of colonoscopy to quantitatively assess endoscopic technical performance. DESIGN: Prospective cohort study. SETTING: Tertiary-care academic medical center. POPULATION: This study involved physicians who perform colonoscopy. INTERVENTION: Application of a kinematics data collection system to colonoscopy evaluation. MAIN OUTCOME MEASUREMENTS: Kinematics data, validated task load assessment instrument, and technical difficulty visual analog scale. RESULTS: All 13 participants completed the colonoscopy to the terminal ileum on the standard colon model. Attending physicians reached the terminal ileum quicker than fellows (median time, 150.19 seconds vs 299.86 seconds; p<.01) with reduced path lengths for all 4 sensors, decreased flex (1.75 m vs 3.14 m; P=.03), smaller tip angulation, reduced absolute roll, and lower curvature of the endoscope. With performance of attending physicians serving as the expert reference standard, the mean kinematic score increased by 19.89 for each decrease in postgraduate year (P<.01). Overall, fellows experienced greater mental, physical, and temporal demand than did attending physicians. LIMITATION: Small cohort size. CONCLUSION: Kinematic data and score calculation appear useful in the evaluation of colonoscopy technical skill levels. The kinematic score appears to consistently vary by year of training. Because this assessment is nonsubjective, it may be an improvement over current methods for determination of competence. Ongoing studies are establishing benchmarks and characteristic profiles of skill groups based on kinematics data.

Hearts of surviving MLP-KO mice show transient changes of intracellular calcium handling.

The muscle Lim protein knock-out (MLP-KO) mouse model is extensively used for studying the pathophysiology of dilated cardiomyopathy. However, explanation is lacking for the observed long survival of the diseased mice which develop until adulthood despite the gene defect, which theoretically predestines them to early death due to heart failure. We hypothesized that adaptive changes of cardiac intracellular calcium (Ca(i)(2+)) handling might explain the phenomenon. In order to study the progression of changes in cardiac function and Ca(i)(2+) cycling, myocardial Ca(i)(2+)-transients recorded by Indo-1 surface fluorometry were assessed with concomitant measurement of hemodynamic performance in isolated Langendorff-perfused hearts of 3- and 9-month old MLP-KO animals. Hearts were challenged with beta-agonist isoproterenol and the sarcoplasmic reticular Ca(2+)-ATPase (SERCA2a) inhibitor cyclopiazonic acid (CPA). Cardiac mRNA content and levels of key Ca(2+) handling proteins were also measured. A decline in lusitropic function was observed in 3-month old, but not in 9-month old MLP-KO mice under unchallenged conditions. beta-adrenergic responses to isoproterenol were similar in all the studied groups. The CPA induced an increase in end-diastolic Ca(i)(2+)-level and a decrease in Ca(2+)-sequestration capacity in 3-month old MLP-KO mice compared to age-matched controls. This unfavorable condition was absent at 9 months of age. SERCA2a expression was lower in 3-month old MLP-KO than in the corresponding controls and in 9-month old MLP-KO hearts. Our results show time-related recovery of hemodynamic function and an age-dependent compensatory upregulation of Ca(i)(2+) handling in hearts of MLP-KO mice, which most likely involve the normalization of the expression of SERCA2a in the affected hearts.

Breast Cancer: Lifestyle, the Human Gut Microbiota/Microbiome, and Survivorship.

Patients with a current diagnosis of breast cancer are enjoying dramatic cure rates and survivorship secondary to an increase in awareness, earlier detection, and more effective therapies. Although strategies such as Breast Cancer Awareness Month in October focus on early detection, lifestyle changes are seldom discussed other than dietary concerns and physical activity. Lifestyle modifications centered on diet and exercise have been demonstrated to affect overall disease-free survival in breast cancer. Since the early 2000s, the role of the human gut microbiota and its relation to breast cancer has become a major area of interest in the scientific and medical community. We live and survive owing to the symbiotic relationship with the microorganisms within us: the human microbiota. Scientific advances have identified a subset of the gut microbiota: the estrobolome, those bacteria that have the genetic capability to metabolize estrogen, which plays a key role in most breast cancers. Recent research provides evidence that the gut microbiome plays a substantial role in estrogen regulation. Gut microbiota diversity appears to be an essential component of overall health, including breast health. Future research attention should include a more extensive focus on the role of the human gut microbiota in breast cancer.

Protein kinase C isoenzymes differentially regulate the differentiation-dependent expression of adhesion molecules in human epidermal keratinocytes.

Epidermal expression of adhesion molecules such as desmogleins (Dsg) and cadherins is strongly affected by the differentiation status of keratinocytes. We have previously shown that certain protein kinase C (PKC) isoforms differentially alter the growth and differentiation of human epidermal HaCaT keratinocytes. In this paper, using recombinant overexpression and RNA interference, we define the specific roles of the different PKC isoenzymes in modulation of expression of adhesion molecules in HaCaT keratinocytes. The level of Dsg1, a marker of differentiating keratinocytes, was antagonistically regulated by two Ca-independent 'novel' nPKC isoforms; i.e. it increased by the differentiation-promoting nPKCdelta and decreased by the growth-promoting nPKCepsilon. The expression of Dsg3 (highly expressed in proliferating epidermal layers) was conversely regulated by these isoenzymes, and was also inhibited by the differentiation inducer Ca-dependent 'conventional' cPKCalpha. Finally, the expression of P-cadherin (a marker of proliferating keratinocytes) was regulated by all of the examined PKCs, also in an antagonistic manner (inhibited by cPKCalpha/nPKCdelta and stimulated by cPKCbeta/nPKCepsilon). Collectively, the presented results strongly argue for the marked, differential, and in some instances antagonistic roles of individual Ca-dependent and Ca-independent PKC isoforms in the regulation of expression of adhesion molecules of desmosomes and adherent junctions in human epidermal keratinocytes.

Endocannabinoids enhance lipid synthesis and apoptosis of human sebocytes via cannabinoid receptor-2-mediated signaling.

We had previously shown that both locally produced endocannabinoids and exocannabinoids, via cannabinoid receptor-1 (CB1), are powerful inhibitors of human hair growth. To further investigate the role of the cannabinoid system in pilosebaceous unit biology, we have explored in the current study whether and how endocannabinoids have an impact on human sebaceous gland biology, using human SZ95 sebocytes as cell culture model. Here, we provide the first evidence that SZ95 sebocytes express CB2 but not CB1. Also, prototypic endocannabinoids (arachidonoyl ethanolamide/anandamide, 2-arachidonoyl glycerol) are present in SZ95 sebocytes and dose-dependently induce lipid production and (chiefly apoptosis-driven) cell death. Endocannabinoids also up-regulate the expression of key genes involved in lipid synthesis (e.g., PPAR transcription factors and some of their target genes). These actions are selectively mediated by CB2-coupled signaling involving the MAPK pathway, as revealed by specific agonists/antagonists and by RNA interference. Because cells with "silenced" CB2 exhibited significantly suppressed basal lipid production, our results collectively suggest that human sebocytes utilize a paracrine-autocrine, endogenously active, CB2-mediated endocannabinoid signaling system for positively regulating lipid production and cell death. CB2 antagonists or agonists therefore deserve to be explored in the management of skin disorders characterized by sebaceous gland dysfunctions (e.g., acne vulgaris, seborrhea, dry skin).

TRP channels as novel players in the pathogenesis and therapy of itch.

Itch (pruritus) is a sensory phenomenon characterized by a (usually) negative affective component and the initiation of a special behavioral act, i.e. scratching. Older studies predominantly have interpreted itch as a type of pain. Recent neurophysiological findings, however, have provided compelling evidence that itch (although it indeed has intimate connections to pain) rather needs to be understood as a separate sensory modality. Therefore, a novel pruriceptive system has been proposed, within which itch-inducing peripheral mediators (pruritogens), itch-selective receptors (pruriceptors), sensory afferents and spinal cord neurons, and defined, itch-processing central nervous system regions display complex, layered responses to itch. In this review, we begin with a current overview on the neurophysiology of pruritus, and distinguish it from that of pain. We then focus on the functional characteristics of the large family of transient receptor potential (TRP) channels in skin-coupled sensory mechanisms, including itch and pain. In particular, we argue that - due to their expression patterns, activation mechanisms, regulatory roles, and pharmacological sensitivities - certain thermosensitive TRP channels are key players in pruritus pathogenesis. We close by proposing a novel, TRP-centered concept of pruritus pathogenesis and sketch important future experimental directions towards the therapeutic targeting of TRP channels in the clinical management of itch.

Protein kinase C protects from DNA damage-induced necrotic cell death by inhibiting poly(ADP-ribose) polymerase-1.

The goal of the current study, conducted in freshly isolated thymocytes was (1) to investigate the possibility that the activation of poly(ADP-ribose) polymerase-1 (PARP-1) in an intact cell can be regulated by protein kinase C (PKC) mediated phosphorylation and (2) to examine the consequence of this regulatory mechanism in the context of cell death induced by the genotoxic agent. In cells stimulated by the PKC activating phorbol esters, DNA breakage was unaffected, PARP-1 was phosphorylated, 1-methyl-3-nitro-1-nitrosoguanidine-induced PARP activation and cell necrosis were suppressed, with all these effects attenuated by the PKC inhibitors GF109203X or Gö6976. Inhibition of cellular PARP activity by PKC-mediated phosphorylation may provide a plausible mechanism for the previously observed cytoprotective effects of PKC activators.

Investigation of micronized titanium dioxide penetration in human skin xenografts and its effect on cellular functions of human skin-derived cells.

Titanium dioxide (TiO2) nanoparticles are ubiquitously used materials in everyday life (e.g. paints,household products and plastic goods). However, despite the wide array of common applications, their pathogenetic role was also suggested under certain conditions (e.g. pulmonary neoplasias and lung fibrosis). From a dermatological point of view, it is also of great importance that TiO2 also serves as a physical photoprotective agent in sunscreens and is widely used in various cosmetic products. However, the effect of TiO2 on human cutaneous functions is still unknown. Therefore, in the current study, we investigated the in vivo penetration of TiO2 via human skin transplanted to immunodeficient mice and,furthermore, we measured the in vitro effects of nanoparticles on various functional properties of numerous epidermal and dermal cells in culture. Hereby, using various nuclear microscopy methods, we provide the first evidence that TiO2nanoparticles in vivo do not penetrate through the intact epidermal barrier. However, we also report that TiO2, when exposed directly to cell cultures in vitro, exerts significant and cell-type dependent effects on such cellular functions as viability, proliferation, apoptosis and differentiation. Therefore, our novel findings will hopefully inspire one to systemically explore in future, clinically oriented trials whether there is indeed a risk from micronized TiO2-containing products on skin with an impaired stratum corneum barrier function.

Inhibition of human hair follicle growth by endo- and exocannabinoids.

Recent studies strongly suggest that the cannabinoid system is a key player in cell growth control. Since the organ-culture of human hair follicles (HF) offers an excellent, clinically relevant model for complex tissue interaction systems, we have asked whether the cannabinoid system plays a role in hair growth control. Here, we show that human scalp HF, intriguingly, are both targets and sources of endocannabinoids. Namely, the endocannabinoid N-arachidonoylethanolamide (anandamide, AEA) as well as the exocannabinnoid delta (9) -tetrahydrocannabinol dose-dependently inhibited hair shaft elongation and the proliferation of hair matrix keratinocytes, and induced intraepithelial apoptosis and premature HF regression (catagen). These effects were inhibited by a selective antagonist of cannabinoid receptor-1 (CB1). In contrast to CB2, CB1 was expressed in a hair cycle-dependent manner in the human HF epithelium. Since we successfully identified the presence of endocannabinoids in human HF, our data strongly suggest that human HF exploit a CB1-mediated endocannabinoid signaling system for negatively regulating their own growth. Clinically, CB1 agonists may therefore help to manage unwanted hair growth, while CB1 antagonists might counteract hair loss. Finally, human HF organ culture offers an instructive, physiologically relevant new research tool for dissecting "nonclassical" effects of endocannabinoids and their receptor-mediated signaling in general.

Protein kinase C-beta and -delta isoenzymes promote arachidonic acid production and proliferation of MonoMac-6 cells.

In this study, we investigated the putative roles of certain protein kinase C (PKC) isoenzymes in the regulation of proliferation and arachidonic acid (AA) release in the human monocytoid MonoMac-6 cell line. Experiments employing specific PKC inhibitors and molecular biological methods (RNA-interference, recombinant overexpression) revealed that the two dominantly expressed isozymes, i.e., the "conventional" cPKCbeta and the "novel" nPKCdelta, promote AA production and cellular proliferation. In addition, using different phospholipase A(2) (PLA(2)) inhibitors, we were able to show that the calcium-independent iPLA(2) as well as diacylglycerol lipase (but not the cytosolic PLA(2)) function as "downstream" targets of cPKCbeta and nPKCdelta. In addition, we have also found that, among the other existing PKC isoforms, cPKCalpha plays a minor inhibitory role, whereas nPKCvarepsilon and aPKCzeta apparently do not regulate these cellular processes. In conclusion, in this paper we provide the first evidence that certain PKC isoforms play pivotal, specific, and (at least partly) antagonistic roles in the regulation of AA production and cellular proliferation of human monocytoid MonoMac-6 cells.

The analgesic drug, tramadol, acts as an agonist of the transient receptor potential vanilloid-1.

BACKGROUND: Tramadol is an effective analgesic substance widely used in medical practice. Its therapeutic action have been mainly attributed to the activation of mu-opioid receptors as well as to the inhibition of neurotransmitter reuptake mechanisms and various voltage- and ligand-gated ion channels of the nociceptive system. As transient receptor potential vanilloid-1 (TRPV1, "the capsaicin receptor") has been shown to function as a central integrator molecule of pain sensation, our aim in the current study was to define the involvement of TRPV1 in the complex mechanism of action of tramadol. METHODS: To achieve these goals, we used single-cell Ca-imaging as well as fluorescent image plate reader assays on Chinese hamster ovary (CHO) cells heterologously over-expressing TRPV1. RESULTS: We found that (1) tramadol, similar to the well-known TRPV1 agonist, capsaicin, significantly increased [Ca(2+)](i) of TRPV1-CHO cells in a concentration-dependent fashion; (2) its effect was reversibly prevented by the TRPV1 antagonist capsazepine; (3) repeated application of tramadol resulted in marked tachyphylaxis; and (4) tramadol did not modify [Ca(2+)](i) in control (empty vector expressing) CHO cells. CONCLUSIONS: Collectively, these findings strongly support the intriguing and novel concept that tramadol acts as an agonist of TRPV1. Considering that activation of TRPV1 on sensory neurons is followed by a local release of vasoactive neuropeptides and a marked desensitization of the afferent fibers (hence termination of pain sensation), our findings may equally explain both the desired analgesic as well as the often-seen, yet "unexpected," local side effects (e.g., initiation of burning pain and erythema) of tramadol.

Lifestyle Medicine: A Brief Review of Its Dramatic Impact on Health and Survival.

By ignoring the root causes of disease and neglecting to prioritize lifestyle measures for prevention, the medical community is placing people at harm. Advanced nations, influenced by a Western lifestyle, are in the midst of a health crisis, resulting largely from poor lifestyle choices. Epidemiologic, ecologic, and interventional studies have repeatedly indicated that most chronic illnesses, including cardiovascular disease, cancer, and type 2 diabetes, are the result of lifestyles fueled by poor nutrition and physical inactivity.In this article, we describe the practice of lifestyle medicine and its powerful effect on these modern instigators of premature disability and death. We address the economic benefits of prevention-based lifestyle medicine and its effect on our health care system: A system on the verge of bankruptcy. We recommend vital changes to a disastrous course. Many deaths and many causes of pain, suffering, and disability could be circumvented if the medical community could effectively implement and share the power of healthy lifestyle choices. We believe that lifestyle medicine should become the primary approach to the management of chronic conditions and, more importantly, their prevention. For future generations, for our own health, and for the Hippocratic Oath we swore to uphold ("First do no harm"), the medical community must take action. It is our hope that the information presented will inspire our colleagues to pursue lifestyle medicine research and incorporate such practices into their daily care of patients. The time to make this change is now.

Apico-basal inhomogeneity in distribution of ion channels in canine and human ventricular myocardium.

OBJECTIVES: The aim of the present study was to compare the apico-basal distribution of ion currents and the underlying ion channel proteins in canine and human ventricular myocardium. METHODS: Ion currents and action potentials were recorded in canine cardiomyocytes, isolated from both apical and basal regions of the heart, using whole-cell voltage clamp techniques. Density of channel proteins in canine and human ventricular myocardium was determined by Western blotting. RESULTS: Action potential duration was shorter and the magnitude of phase-1 repolarization was significantly higher in apical than basal canine myocytes. No differences were observed in other parameters of the action potential or cell capacitance. Amplitude of the transient outward K(+) current (29.6+/-5.7 versus 16.5+/-4.4 pA/pF at +65 mV) and the slow component of the delayed rectifier K(+) current (5.61+/-0.43 versus 2.14+/-0.18 pA/pF at +50 mV) were significantly larger in apical than in basal myocytes. Densities of the inward rectifier K(+) current, rapid delayed rectifier K(+) current, and L-type Ca(2+) current were similar in myocytes of apical and basal origin. Apico-basal differences were found in the expression of only those channel proteins which are involved in mediation of the transient outward K(+) current and the slow delayed rectifier K(+) current: expression of Kv1.4, KChIP2, KvLQT1 and MinK was significantly higher in apical than in basal myocardium in both canine and human hearts. CONCLUSIONS: The results suggest that marked apico-basal electrical inhomogeneity exists in the canine-and probably in the human-ventricular myocardium, which may result in increased dispersion, and therefore, cannot be ignored when interpreting ECG recordings, pathological alterations, or drug effects.