Charge movement currents (IQ) and calcium transients (delta[Ca2+]) were measured simultaneously in frog skeletal muscle fibers, voltage clamped in a double vaseline gap chamber, using Antipyrylazo III as the calcium indicator. The rate of release of calcium from the SR (Rrel) was calculated from the calcium transients using the removal model of Melzer, W., E. Rios, and M. F. Schneider (1987. Biophys. J. 51:849-863.). IQ and delta [Ca2+] were calculated for 100 ms depolarizing test pulses to membrane potentials from -30 to +20 mV. To eliminate an inactivating component of Rrel, each test pulse was preceded by a large, fixed prepulse to +20 mV. The resulting Rrel records, which represent the noninactivating component of Rrel, were compared with integral of IQdt.(Q), the total charge that moves. The voltage dependence of the steady state Rrel was steeper then that of Q and shifted to the right. During depolarization, the Rrel waveform was similar to that of Q but was delayed by several ms, while, during repolarization, Rrel preceded Q. All of these results could be explained with a Hodgkin-Huxley type model for E-C coupling in which four voltage sensors in the t-tubule membrane which give rise to IQ must all be in their activating positions for the calcium release channel in the SR membrane to open. his model is consistent with the structural architecture of the triadic junction in which four dihydropyridine receptors (the voltage sensors for E-C coupling) in the t-tubule membrane are closely associated with each ryanodine receptor(the calcium release channel) in the SR membrane [Block, B. A., T. Imagawa, K. P. Campbell, and C. Franzini-Armstrong. 1988. J.Cell. Biol. 107:2587-2600.]). Some aspects of this work have appeared in abstract form (Simon, B. J., and D. Hill. 1991. Biophys. J.59:64a. ([Abstr.]).

Background— A noninvasive biomarker that could accurately diagnose acute rejection (AR) in heart transplant recipients could obviate the need for surveillance endomyocardial biopsies. We assessed the performance metrics of a novel high-sensitivity cardiac troponin I (cTnI) assay for this purpose. Methods and Results— Stored serum samples were retrospectively matched to endomyocardial biopsies in 98 cardiac transplant recipients, who survived ≥3 months after transplant. AR was defined as International Society for Heart and Lung Transplantation grade 2R or higher cellular rejection, acellular rejection, or allograft dysfunction of uncertain pathogenesis, leading to treatment for presumed rejection. cTnI was measured with a high-sensitivity assay (Abbott Diagnostics, Abbott Park, IL). Cross-sectional analyses determined the association of cTnI concentrations with rejection and International Society for Heart and Lung Transplantation grade and the performance metrics of cTnI for the detection of AR. Among 98 subjects, 37% had ≥1 rejection episode. cTnI was measured in 418 serum samples, including 35 paired to a rejection episode. cTnI concentrations were significantly higher in rejection versus nonrejection samples (median, 57.1 versus 10.2 ng/L; P <0.0001) and increased in a graded manner with higher biopsy scores ( P trend <0.0001). The c -statistic to discriminate AR was 0.82 (95% confidence interval, 0.76–0.88). Using a cut point of 15 ng/L, sensitivity was 94%, specificity 60%, positive predictive value 18%, and negative predictive value 99%. Conclusions— A high-sensitivity cTnI assay seems useful to rule out AR in cardiac transplant recipients. If validated in prospective studies, a strategy of serial monitoring with a high-sensitivity cTnI assay may offer a low-cost noninvasive strategy for rejection surveillance.

EMB remains the gold standard for cardiac allograft rejection surveillance. However, recent data indicate potential clinical utility for serial monitoring of natriuretic peptides. If further investigation into highly sensitive troponin assays confirms the positive data so far reported, further efforts directed toward a longitudinal-based rejection surveillance algorithm incorporating both troponin and BNP may identify a strategy that could serve as an alternative to EMB.

The development of new biological and chemical instruments for research and diagnostic applications is often slowed by the cost, specialization, and custom nature of these instruments. New instruments are built from components that are drawn from a host of different disciplines and not designed to integrate together, and once built, an instrument typically performs a limited number of tasks and cannot be easily adapted for new applications. Consequently, the process of inventing new instruments is very inefficient, especially for researchers or clinicians in resource-limited settings. To improve this situation, we propose that a family of standardized multidisciplinary components is needed, a set of “building blocks” that perform a wide array of different tasks and are designed to integrate together. Using these components, scientists, engineers, and clinicians would be able to build custom instruments for their own unique needs quickly and easily. In this work we present the foundation of this set of components, a system we call Multifluidic Evolutionary Components (MECs). “Multifluidic” conveys the wide range of fluid volumes MECs operate upon (from nanoliters to milliliters and beyond); “multi” also reflects the multiple disciplines supported by the system (not only fluidics but also electronics, optics, and mechanics). “Evolutionary” refers to the design principles that enable the library of MEC parts to easily grow and adapt to new applications. Each MEC “building block” performs a fundamental function that is commonly found in biological or chemical instruments, functions like valving, pumping, mixing, controlling, and sensing. Each MEC also has a unique symbol linked to a physical definition, which enables instruments to be designed rapidly and efficiently using schematics. As a proof-of-concept, we use MECs to build a variety of instruments, including a fluidic routing and mixing system capable of manipulating fluid volumes over five orders of magnitude, an acid-base titration instrument suitable for use in schools, and a bioreactor suitable for maintaining and analyzing cell cultures in research and diagnostic applications. These are the first of many instruments that can be built by researchers, clinicians, and students using the MEC system.