Intracellular calcium (Ca2+) is a ubiquitous second messenger. Information is encoded in the magnitude, frequency, and spatial organization of changes in the concentration of cytosolic free Ca2+. Regenerative spiral waves of release of free Ca2+ were observed by confocal microscopy in Xenopus laevis oocytes expressing muscarinic acetylcholine receptor subtypes. This pattern of Ca2+ activity is characteristic of an intracellular milieu that behaves as a regenerative excitable medium. The minimal critical radius for propagation of focal Ca2+ waves (10.4 micrometers) and the effective diffusion constant for the excitation signal (2.3 x 10(-6) square centimeters per second) were estimated from measurements of velocity and curvature of circular wavefronts expanding from foci. By modeling Ca2+ release with cellular automata, the absolute refractory period for Ca2+ stores (4.7 seconds) was determined. Other phenomena expected of an excitable medium, such as wave propagation of undiminished amplitude and annihilation of colliding wavefronts, were observed.

Background-Some patients with severe symptomatic aortic stenosis (AS) do not undergo aortic valve replacement (AVR) despite demonstrated symptomatic and survival advantages and despite unequivocal guideline recommendations for surgical evaluation. Methods and Results-In

BackgroundIn Canada, new models of orthopaedic care involving advanced practice physiotherapists (APP) are being implemented. In these new models, aimed at improving the efficiency of care for patients with musculoskeletal disorders, APPs diagnose, triage and conservatively treat patients. Formal validation of the efficiency and appropriateness of these emerging models is scarce. The purpose of this study is to assess the diagnostic agreement of an APP compared to orthopaedic surgeons as well as to assess treatment concordance, healthcare resource use, and patient satisfaction in this new model.Methods120 patients presenting for an initial consult for hip or knee complaints in an outpatient orthopaedic hospital clinic in Montreal, Canada, were independently assessed by an APP and by one of three participating orthopaedic surgeons. Each health care provider independently diagnosed the patients and provided triage recommendations (conservative or surgical management). Proportion of raw agreement and Cohen’s kappa were used to assess inter-rater agreement for diagnosis, triage, treatment recommendations and imaging tests ordered. Chi-Square tests were done in order to compare the type of conservative treatment recommendations made by the APP and the surgeons and Student t-tests to compare patient satisfaction between the two types of care.ResultsThe majority of patients assessed were female (54%), mean age was 54.1 years and 91% consulted for a knee complaint. The raw agreement proportion for diagnosis was 88% and diagnostic inter-rater agreement was very high (κ=0.86; 95% CI: 0.80-0.93). The triage recommendations (conservative or surgical management) raw agreement proportion was found to be 88% and inter-rater agreement for triage recommendation was high (κ=0.77; 95% CI: 0.65-0.88). No differences were found between providers with respect to imaging tests ordered (p≥0.05). In terms of conservative treatment recommendations made, the APP gave significantly more education and prescribed more NSAIDs, joint injections, exercises and supervised physiotherapy (p<0.05). Patient satisfaction was significantly higher for APP care than for the surgeons care (p<0.05).ConclusionThe diagnoses and triage recommendations for patients with hip and knee disorders made by the APP were similar to the orthopaedic surgeons. These results provide evidence supporting the APP model for orthopaedic care.

In PVT, the thrombus size imaged with TEE is a significant independent predictor of outcome. Transesophageal echocardiography can identify low-risk groups for thrombolysis irrespective of symptom severity and is therefore recommended in the management of prosthetic valve thrombosis.

Many cell membrane receptors stimulate the phosphoinositide (PI) cycle, which produces complex intracellular calcium signals that regulate diverse processes such as secretion and transcription. A major messenger of this cycle, inositol 1,4,5-triphosphate (IP3), stimulates its receptor channel on the endoplasmic reticulum to release calcium into the cytosol. Activation of the PI cycle also induces calcium influx, which refills the intracellular calcium stores. Confocal microscopy was used to show that receptor-activated calcium influx, enhanced by hyperpolarization, modulates the frequency and velocity of IP3-dependent calcium waves in Xenopus laevis oocytes. These results demonstrate that transmembrane voltage and calcium influx pathways may regulate spatial and temporal patterns of IP3-dependent calcium release.

Calcium release from intracellular stores is a point of convergence for a variety of receptors involved in cell signaling. Consequently, the mechanism(s) by which cells differentiate between individual receptor signals is central to transmembrane communication. There are significant differences in timing and magnitude of Ca2+ release stimulated by the m2 and m3 muscarinic acetylcholine receptors. The m2 receptors couple to a pertussis toxin-sensitive G protein to activate phosphatidyl inositol hydrolysis weakly and to stimulate small, delayed and oscillatory chloride currents. In contrast, m3 receptors potently activate phosphatidyl inositol hydrolysis and stimulate large, rapid and transient chloride currents by a pertussis toxin-insensitive G protein pathway. Using confocal microscopy, we now show that the m2- and m3-coupled Ca2+ release pathways can also be spatially distinguished. At submaximal acetylcholine concentrations, both receptors stimulated pulses of Ca2+ release from discrete foci in random, periodic and frequently bursting patterns of activity. But maximal stimulation of m2 receptors increased the number of focal release sites, whereas m3 receptors invariably evoked a Ca2+ wave propagating rapidly just beneath the plasma membrane surface. Analysis of pertussis toxin sensitivity and hybrid m2-m3 muscarinic acetylcholine receptors confirmed that these Ca2+ release patterns represent distinct cell signalling pathways.

Doppler TTE is the primary means to diagnose AVR obstruction; hemodynamic catheterization is not routinely needed. In unselected patients with mechanical AVR obstruction, TEE differentiation of pannus or thrombus from mismatch is challenging.

Biological excitability enables the rapid transmission of physiological signals over distance. Using confocal fluorescence microscopy, we previously reported circular, planar, and spiral waves of Ca2+ in Xenopus laevis oocytes that annihilated one another upon collision. We present experimental evidence that the excitable process underlying wave propagation depends on Ca2+ diffusion and does not require oscillations in inositol (1,4,5)trisphosphate (IP3) concentration. Extending an existing ordinary differential equation (ODE) model of Ca2+ oscillations to two spatial dimensions, we develop a partial differential equation (PDE) model of Ca2+ excitability. The model assumes that cytosolic Ca2+ couples neighboring Ca2+ release sites. This simple PDE model qualitatively reproduces our experimental observations.