Smectic C to cubic phase transition of 4'-n-docosyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-22) and alternating-current electric field effect.

Smectic C (SmC) to cubic (Cub) phase transition behavior of 4'-n-docosyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-22) and alternating-current (AC) electric field effect on the SmC phase were examined. The most important and unexpected finding is that even at a temperature 8 K below the zero-field SmC to Cub phase transition temperature (T(SmC-Cub) approximately 408 K) determined previously for the compound and without field, the Cub phase growth occurs, after a very long induction period of several hours. The X-ray diffraction measurements revealed the formation of an Im3m-type Cub phase at the temperature. It is suggested that the "true" transition temperature, which is difficult to determine precisely, exists around 396 K. The time-dependence of the Cub phase growth both without field and under field was analyzed using the well-known Avrami equation, implying the nucleation and growth mechanism mainly operating in the SmC to Cub phase transformation. The fact uncovered is that between 408 and 396 K, the SmC to Cub transformation is virtually prohibited by the strongly limited nucleation. It is concluded that the effect of the electric field on the transition is to promote the nucleation of the Cub phase in the temperature region where the Cub phase is potentially more stable than the precursory SmC phase.

In situ measurements of crossbridge dynamics and lattice spacing in rat hearts by x-ray diffraction: sensitivity to regional ischemia.

BACKGROUND: Synchrotron radiation has been used to analyze crossbridge dynamics in isolated papillary muscle and excised perfused hearts with the use of x-ray diffraction techniques. We showed that these techniques can detect regional changes in rat left ventricle contractility and myosin lattice spacing in in situ ejecting hearts in real time. Furthermore, we examined the sensitivity of these indexes to regional ischemia. METHODS AND RESULTS: The left ventricular free wall of spontaneously beating rat hearts (heart rate, 290 to 404 bpm) was directly exposed to brief high-flux, low-emittance x-ray beams provided at SPring-8. Myosin mass transfer to actin filaments was determined as the decrease in reflection intensity ratio (intensity of 1,0 plane over the 1,1 plane) between end-diastole and end-systole. The distance between 1,0 reflections was converted to a lattice spacing between myosin filaments. We found that mass transfer (mean, 1.71+/-0.09 SEM, n=13 hearts) preceded significant increases in lattice spacing (2 to 5 nm) during systole in nonischemic pericardium. Left coronary occlusion eliminated increases in lattice spacing and severely reduced mass transfer (P<0.01) in the ischemic region. CONCLUSIONS: Our results suggest that x-ray diffraction techniques permit real-time in situ analysis of regional crossbridge dynamics at molecular and fiber levels that might also facilitate investigations of ventricular output regulation by the Frank-Starling mechanism.

Electric field-induced cubic phase in 4'-n-docosyloxy-3'-nitrobiphenyl-4-carboxylic acid.

We examine the influence of an alternating-current electric field on the lamellar smectic C (SmC) phase of 4'-n-docosyloxy-3'-nitrobiphenyl-4-carboxylic acid, and the formation of a field-induced cubic (Cub) phase with optical isotropy was observed for the first time. The induction was realized down to a temperature 10 K below the zero-field SmC to Cub phase transition temperature (TSmC-Cub). The formation of the induced Cub phase gave rise to a gradual increase of the shear storage modulus, and the modulus recovered quickly in response to the removal of the field, which is of interest as future applications to the stress transferring device.

Development of cardiac rhythms in birds.

Heart rate (HR) in avian embryos developing inside an eggshell has been measured by various means while maintaining adequate gas exchange through the eggshell. This is an important requirement in order to avoid adverse effects of impeding gas exchange on the cardiac rhythms of developing embryos. The present report is a review of our ontogenetic study on embryonic HR, which was measured with fulfillment of the above requirement and also hatchling HR measured non-invasively. Firstly, we reviewed measurements of daily changes (developmental patterns) in embryonic mean heart rate (MHR), which were determined from a short-term measurement of HR once a day, in 34 species of altricial and precocial birds. The allometric relationship between the MHR during pipping in altricial birds and their fresh egg masses was the same as that between the MHR at 80% of incubation duration and fresh egg masses in pre-cocial birds. Secondly, we presented the developmental patterns of MHR in chick embryos and hatchlings, which were determined from long-term, continuous measurement of HR before, during and after hatching. The ultradian and circadian rhythms of HR were clearly shown in embryos and hatchlings, respectively. Thirdly, we summarized instantaneous HR fluctuations: HR variability and HR irregularities, in chick embryos and hatchlings. The distinctive patterns were shown in pre-pipped and pipped embryos and newly hatched chicks, individually, which were partly related to autonomic nervous functions and physiological functions.

Low-frequency oscillation of instantaneous heart rate in newly hatched chicks.

Instantaneous heart rate (IHR) of chickens began to fluctuate on days 13-14 of incubation and heart rate (HR) fluctuations became augmented towards hatching and increased further after hatching. IHR fluctuations of newly hatched chicks have been categorized into three types: type I HR variability (HRV), which is high-frequency oscillation; type II HRV, which is low-frequency oscillation; and type III HR irregularities (HRI), which are irregular HR accelerations. The present experiment was carried out to investigate the origin of type II HR oscillations. Following previous evidence, we assumed that the low-frequency oscillation of HR in newly hatched chicks was related to thermoregulation and changed by environmental temperature. Eventually, type II HRV was produced or augmented by exposure of hatchlings to lowered ambient temperature and was abolished by exposure to elevated environmental temperature. The hatchlings that were exposed to large temperature decreases tended to increase their HR more than those exposed to small temperature decreases, and vice versa. The HR oscillation accompanied by an elevation of HR baseline in response to cooling may be a phenomenon related to thermoregulation in chick hatchlings.