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In an earlier study, we experimentally mimicked the effects of mechanical interaction between different regions of the ventricular wall by allowing pairs of independently maintained cardiac muscle fibers to interact mechanically in series or in parallel. This simple physiological model of heterogeneous myocardium, which has been termed "duplex," has provided new insight into basic effects of cardiac electromechanical heterogeneity. Here, we present a novel "hybrid duplex," where one of the elements is an isolated cardiac muscle and the other a "virtual cardiac muscle." The virtual muscle is represented by a computational model of cardiomyocyte electromechanical activity. We present in detail the computer-based digital control system that governs the mechanical interaction between virtual and biological muscle, the software used for data analysis, and working implementations of the model. Advantages of the hybrid duplex method are discussed, and experimental recordings are presented for illustration and as proof of the principle.

Glycerol-wetted track membranes (poly(ethylene terephthalate)) are suitable for interfacing between a typical TOF chamber (held at an operational pressure of less than 10-6 Torr) and an ambient pressure analyte. Solute concentration aspects of track membrane mediated electrostatic introduction of negative charged species into TOF mass spectrometer were investigated. Glycerol solutions of KCl, KBr, NH4I, and Na2S were used. High-field charge extraction conditions were routinely maintained between the liquid samples (held at ambient pressure) and a grounded grid collector. The latter was positioned just nearby the vacuum facing side of such membranes. Upon establishing a steady-state charge extraction regime, the collector currents were monitored and recorded at various solute concentration levels. Nonlinear, solute concentration dependent, collector currents were observed and found to correspond to our theoretical treatment. Our findings are accounted for and in support of a special, evaporation limited, mechanism for the track membrane mediated high-field extraction of cluster ions.

The multichannel extraction of negative charged particles from solutions of KCI, KBr, KI in glycerol and glycerol + water mixtures has been investigated by time-of-fight mass spectrometry. The charged particles extracted by using specially prepared perforated membranes are cluster ions consisting of deprotonated molecules of glycerol and halogen anions with several attached molecules of glycerol. The energy distribution of particles recorded by mass spectrometry is too broad for them to be the primary ions extracted from liquid. In comparison with traditional electrohydrodynamic ionization, multichannel extraction is shown to have a unique mechanism. The main factors controlling the membrane ion source, are considered, including high electric field formation, ion transport and field evaporation of ions.

The length-dependent activation of contraction is attenuated in the failing myocardium of adult male rats. This pathological change is not seen in adult female rats, possibly because of a protective effect of sex hormones. The present study evaluated length-dependent changes in isometric twitch, Ca(2+) transient (CaT) and action potential (AP) in the right ventricular myocardium of impuberal healthy male and female rats (control) and in rats treated with a single injection of 50 mg/kg monocrotaline (MCT). Compared with sex-matched control rats, MCT-treated male and female rats exhibited increased right ventricular weight (134% and 142% of control, respectively), decreased left ventricular weight (72% and 79%), twitch attenuation (48.8 ± 2.7% and 57.5 ± 1.2%) and prolongation (125 ± 3% and 127 ± 2%), CaT attenuation (37.8 ± 0.4% and 39.1 ± 1.1%) and prolongation (114 ± 1% and 116 ± 1%) and AP prolongation at 90% repolarization (195 ± 2% and 203 ± 1%). The MCT-treated male rats exhibited a 50% lower integral magnitude and an approximately 25% larger time-to-peak 'bump' compared with control male rats. These parameters in MCT-treated female rats tended to show similar changes to those seen in the control female rats, with no significant difference between the two groups. In all groups, integral magnitude and time-to-peak 'bump' increased with length. In conclusion, the length-dependent activation of contraction was equally blunted in the failing right ventricular myocardium of impuberal male and female rats. This was related to changes in CaT and AP, which were similar between male and female rats. Therefore, puberty is necessary for manifestation of the protective effects of sex hormones on this remodelling.

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