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At least 469 records · Page 26Linked to original sources
PubMed2006

Connexin30.2 containing gap junction channels decelerate impulse propagation through the atrioventricular node.

In the mammalian heart, gap junction channels between electrically coupled cardiomyocytes are necessary for impulse propagation and coordinated contraction of atria and ventricles. Recently, mouse connexin30.2 (Cx30.2) was shown to be expressed in the cardiac conduction system, predominantly in sinoatrial and atrioventricular (AV) nodes. The corresponding gap junctional channels expressed in HeLa cells exhibit the lowest unitary conductance (9 pS) of all connexin channels. Here we report that Cx30.2 slows down the propagation of excitation through the AV node. Mice expressing a LacZ reporter gene instead of the Cx30.2 coding region (Cx30.2(LacZ/LacZ)) exhibit a PQ interval that is approximately 25% shorter than in WT littermates. By recording atrial, His, and ventricular signals with intracardiac electrodes, we show that this decrease is attributed to significantly accelerated conduction above the His bundle (atrial-His interval: 27.9 +/- 5.1 ms in Cx30.2(LacZ/LacZ) versus 37.1 +/- 4.1 ms in Cx30.2(+/+) mice), whereas HV conduction is unaltered. Atrial stimulation revealed an elevated AV-nodal conduction capacity and faster ventricular response rates during induced episodes of atrial fibrillation in Cx30.2(LacZ/LacZ) mice. Our results show that Cx30.2 contributes to the slowdown of impulse propagation in the AV node and additionally limits the maximum number of beats conducted from atria to ventricles. Thus, it is likely to be involved in coordination of atrial and ventricular contraction and to fulfill a protective role toward pathophysiological states such as atrial tachyarrhythmias (e.g., atrial fibrillation) by preventing rapid conduction to the ventricles potentially associated with hemodynamic deterioration.

Animals↗
PubMed2003

Low force decelerates L-selectin dissociation from P-selectin glycoprotein ligand-1 and endoglycan.

Selectin-ligand interactions mediate the tethering and rolling of circulating leukocytes on vascular surfaces during inflammation and immune surveillance. To support rolling, these interactions are thought to have rapid off-rates that increase slowly as wall shear stress increases. However, the increase of off-rate with force, an intuitive characteristic named slip bonds, is at odds with a shear threshold requirement for selectin-mediated cell rolling. As shear drops below the threshold, fewer cells roll and those that do roll less stably and with higher velocity. We recently demonstrated a low force regime where the off-rate of P-selectin interacting with P-selectin glycoprotein ligand-1 (PSGL-1) decreased with increasing force. This counter-intuitive characteristic, named catch bonds, might partially explain the shear threshold phenomenon. Because L-selectin-mediated cell rolling exhibits a much more pronounced shear threshold, we used atomic force microscopy and flow chamber experiments to determine off-rates of L-selectin interacting with their physiological ligands and with an antibody. Catch bonds were observed at low forces for L-selectin-PSGL-1 interactions coinciding with the shear threshold range, whereas slip bonds were observed at higher forces. These catch-slip transitional bonds were also observed for L-selectin interacting with endoglycan, a newly identified PSGL-1-like ligand. By contrast, only slip bonds were observed for L-selectin-antibody interactions. These findings suggest that catch bonds contribute to the shear threshold for rolling and are a common characteristic of selectin-ligand interactions.

Animals↗
PubMed1996

In utero exposure to low-doses of ionizing radiation decelerates neuronal migration in the developing rat brain.

In order to elucidate the possible mechanisms for the effects of low doses of ionizing radiation on the developing rat cerebral cortex we studied how neuronal migration can be affected by prenatal in utero irradiation. We have demonstrated an effect of ionizing radiation on neuronal migration at doses as low as 15 cGy together with a changing pattern of expression of the neural cell adhesion molecule N-CAM. After a dose of 15 cGy or more there was a reduction in N-CAM immunoreactivity in the matrix cell zone which became apparent about 24 h after exposure and continued until 48 h after exposure. Normal reactivity occurred 3 days after exposure to radiation. However, there was no obvious change in the immunoreactivity for L1, MAP2, tau protein or neurofilament. Our findings suggest the possible role of N-CAM in neuronal migration and also suggest the presence of a threshold in terms of the effects of small radiation doses on the developing cerebral cortex.

Animals↗
PubMed1986

Deceleration of age-associated changes in the preovulatory but not secondary follicle-stimulating hormone surge by progesterone.

Recently, it has been reported that mating can delay the age-associated decline in reproductive function of female rats. Since circulating progesterone (P) levels are elevated for a 2- to 3-wk interval during pregnancy, the following study was conducted to determine whether intermittent elevation in P levels can alter the rate of reproductive aging in female rats. Beginning at 2 mo of age, 4-day-cycling, virgin rats were divided into two groups. In one group, 3 Silastic capsules containing crystalline P were inserted s.c. into each rat while rats in another group each received 1 empty capsule. After 2 wk, the capsules were removed for 2 wk. Thereafter, implantation and removal of capsules was repeated 5 additional times. Rats receiving P capsules became acyclic 3-4 days after exposure to P and resumed cyclicity 4-7 days after removal of P-capsules. One month after the last series of capsules was removed (rats approximately 8-mo-old), rats exhibiting consecutive 4-day cycles were inserted with indwelling atrial cannulae and bled at 4-h intervals from 1400 h on proestrus (Pr) to 1000 h on estrus (E). At 1600 h E, rats were killed and trunk blood was collected. For comparison, a group of 3-mo-old (young) rats was bled on Pr and E. In 8-mo-old rats that received empty capsules, 27% exhibited 4-day cycles compared to 66% of the young rats. However, in contrast to rats that received empty capsules, 63.1% of P-treated rats exhibited 4-day cycles. Surges of preovulatory luteinizing hormone (LH) and follicle-stimulating hormone (FSH) surges were attenuated in 8-mo-old rats given empty capsules compared to young rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1993

Decelerated migration of neocortical neurones in explant culture after exposure to radiation.

We describe a newly devised explant culture system employing rat neocortex in which neurones migrate in a fashion similar to that seen in vivo. Using neocortical explant culture we have demonstrated an effect of ionizing radiation on neuronal migration at doses as low as 10 cGy together with a changing pattern of expression of the neural cell adhesion molecule N-CAM. After a dose of more than 10 cGy there was a significant reduction in N-CAM immunoreactivity in the matrix cell zone. We do not know the reason why the reduction in N-CAM immunoreactivity is so localized, although it is not unlikely that the most active site in terms of N-CAM synthesis is significantly affected by radiation.

Animals↗
PubMed1996

Diagnosis and management of acute aortic valvular disruption secondary to rapid-deceleration trauma.

Acute aortic valve rupture with resultant aortic insufficiency is a rare complication of blunt trauma. We describe a case in which a patient fell 70 feet, sustaining avulsion of two leaflets of the aortic valve along with multiple other injuries, primarily orthopedic. Our case demonstrates that patients with acute aortic regurgitation can be managed nonoperatively if necessary in the acute setting, enabling management of other significant trauma. Subsequent semielective valvular replacement may be undertaken if other injuries must take precedence.

Accidental Falls↗