Electrophysiological responses of cardiac muscle to isoproterenol covalently linked to glass beads

We investigated the effects of isoproterenol aryl glass beads on the electrical properties of cardiac muscle and related these to our previous results concerning biochemical and contractile effects (Ingebretsen et al., Circ, Rs., 40: 474-484, 1977). Beads (10-15) were placed near one end to guinea pig papillary muscles mounted horizontally in a bath perfused with Krebs-Henseleit solution at 30 degrees C and stimulated at 0.2 Hz. The beads produced increased tension and elevation and slight lengthening of the plateau potential when [k+]o = 3.8 mM. After depolarization to a resting potential of -49 mV with [K+]o = 22 mM, isoproterenol beads restored contraction to a comparable extent as occurred with 10(-8) M soluble drug. During field stimulation, action potentials were initiated at the site of bead application and spread decrementally. When beads were placed distal to the site of point stimulation, virtually no excitation could be obtained from cells in the vicinity of the beads. When they were placed close to the stimulating electrode, the beads increased excitability and typical slow action potentials spread to the other end of the muscle. These potentials had the characteristics associated with the slow inward Ca2+ current. The slow channel blocker, D-600, blocked responses to isoproterenol beads. Tetrodotoxin caused responses similar to those obtained with K+ depolarization. The beads probably act by stimulating only a small fraction of the papillary muscle catecholamine receptors. Spread of action potentials from these sites and propagated tension depend on Ca2+ influx, but the nature of an intermediate messenger involved in the propagation of contractions is unknown.     

Quantitative analysis of the plain radiographic appearance of unicameral bone cysts

The reliability and frequency specificity of the 80-Hz amplitude-modulation-following response (80-Hz AMFR) during sleep detected by phase coherence as a measure of the hearing threshold was evaluated in 169 affected ears of 125 children with hearing impairment. The 80-Hz AMFR at a carrier frequency of 1000 Hz was monitored in all 169 ears and the auditory brainstem response (ABR) elicited by 1000-Hz tone pips was evaluated in 93 ears. Both responses were examined during sleep, and the thresholds were compared with the behavioral hearing threshold, which was determined by standard pure-tone audiometry or play audiometry. In 24 ears of 22 children with various patterns of audiogram, the 80-Hz AMFR was examined at different carrier frequencies, and the threshold pattern was compared with the pure-tone audiogram to investigate the frequency specificity of 80-Hz AMFR. The mean and standard deviation of the difference between the 80-Hz AMFR at a carrier frequency of 1000 Hz and pure-tone thresholds of 1000 Hz was 3.8 and 12.9 dB, and that between the ABR and pure-tone thresholds was 6.8 and 14.1 dB, respectively. The threshold patterns of 80-Hz AMFR clearly followed the corresponding audiogram patterns in all types of hearing impairment. The measurement of 80-Hz AMFR thus appears to be accurate in hearing assessment and to have good frequency specificity in children during sleep.     

Uterine and hepatic gene expression in relation to days postpartum, estrus, and pregnancy in postpartum dairy cows

The somatotropic axis consisting of growth hormone, the growth hormone receptor (GHR) insulin-like growth factor (IGF)-I, and IGF binding proteins changes with the stage of lactation and nutrition of the cow and may be 1 mechanism through which lactation and nutrition affect the establishment of pregnancy. The objective of this study was to quantify GHR, IGF-I, and IGF binding protein-2 (IGFBP-2) mRNA in liver and uterine endometrial tissue at 4 stages of lactation (40, 80, 120, and 160 days in milk) and around the time of artificial insemination. Estrus was synchronized with GnRH and PGF_2α, and cows were inseminated 12 h after estrus. Uterine biopsies were collected immediately before the second injection of PGF_2α (before estrus), at the initiation of standing estrus, and 4 d after estrus. Liver biopsies were collected once on 4 d after estrus. The abundance of GHR, IGF-I, and IGFBP-2 mRNA in liver and uterus was determined by real-time quantitative PCR. The amount of liver IGF-I mRNA was positively correlated with plasma IGF-I concentrations. Cows that became pregnant after AI had more GHR and IGFBP-2 mRNA in their liver than cows that did not become pregnant. There was no effect of DIM or pregnancy status on abundance of uterine mRNA; however, uterine GHR and IGF-I mRNA was most abundant at estrus. In summary, cows at different stages of lactation or with different pregnancy statuses had similar quantities of uterine mRNA. In contrast, liver quantities of mRNA differed relative to pregnancy status. These data provide evidence that liver indices of metabolic state may be indicative of pregnancy success.