Demonstration of an inwardly rectifying K+ current component modulated by thyrotropin-releasing hormone and caffeine in GH3 rat anterior pituitary cells

 Reduction of an inwardly rectifying K⁺ current by thyrotropin-releasing hormone (TRH) and caffeine has been considered to be an important determinant of electrical activity increases in GH₃ rat anterior pituitary cells. However, the existence of an inwardly rectifying K⁺ current component was recently regarded as a misidentification of an M-like outward current, proposed to be the TRH target in pituitary cells, including GH₃ cells. In this report, an inwardly rectifying component of K⁺ current is indeed demonstrated in perforated-patch voltage-clamped GH₃ cells. The degree of rectification varied from cell to cell, but both TRH and caffeine specifically blocked a fraction of current with strong rectification in the hyperpolarizing direction. Use of ramp pulses to continuously modify the membrane potential demonstrated a prominent blockade even in cells with no current reduction at voltages at which M-currents are active. Depolarization steps to positive voltages at the maximum of the inward current induced a caffeine-sensitive instantaneous outward current followed by a single exponential decay. The magnitude of this current was modified in a biphasic way according to the duration of the previous hyperpolarization step. The kinetic characteristics of the current are compatible with the possibility that removal from inactivation of a fast-inactivating delayed rectifier causes the hyperpolarization-induced current. Furthermore, the inwardly rectifying current was blocked by astemizole, a potent and selective inhibitor of human ether-á-go-go -related gene (HERG) K⁺ channels. Along with other pharmacological and kinetic evidence, this indicates that the secretagogue-regulated current is probably mediated by a HERG-like K⁺ channel. Addition of astemizole to current-clamped cells induced clear increases in the frequency of action potential production. Thus, an inwardly-rectifying K⁺ current and not an M-like outward current seems to be involved in TRH and caffeine modulation of electrical activity in GH₃ cells. Received: 15 May 1997 / Received after revision and accepted: 24 July 1997     

Analysis of chromosome 6q in Basque families with type 1 diabetes. GEPV-N. Basque-Navarre Endocrinology and Paediatric Group

Over the last few years several studies of linkage between non-HLA loci and type 1 diabetes mellitus have mapped several putative susceptibility genes on chromosome 6q; in fact, positive evidence of linkage and/or association of IDDM5 (6q25), IDDM8 (6q27) and IDDM15 (6q21) with type 1 diabetes has been reported. We have studied these loci in diabetic families of Basque origin, a genetically homogeneous population, to avoid artifactual association results due to admixture within the sample analysed. Statistical analyses of linkage were performed using a transmission disequilibrium test (TDT). We could not confirm linkage for IDDM5, IDDM8 and IDDM15 in our population, possibly due to population-specific differences in genetic susceptibility and/or environmental triggering factors to type 1 diabetes.     

Mechanism of action of baclofen on myocardial and vascular contractility

Department of Anatomy and Physiology of Man and Animals, A. I. Gertsen Leningrad Pedagogic Institute. Department of Pharmacology, Academician I. P. Pavlov First Leningrad Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR A. V. Val'dman.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 106, No. 10, pp. 436–438, October, 1988.     

Magnetic resonance microscopy versus light microscopy in human embryology teaching

A study was carried out on the application of magnetic resonance microscopy (MRM) in teaching prenatal human development. Human embryos measuring 8 mm, 15 mm, 18.5 mm, and 22 mm were fixed in a 4% paraformaldehyde solution and sections obtained with magnetic resonance imaging (MRI) were compared to those prepared for light microscopy (LM), using the same embryos. The MRM and LM slices were of a similar quality. In the MRM sections, embryonic organs and systems were clearly visible, particularly the peripheral and central nervous systems, and the cardiovascular and digestive systems. The digitalization and clarity of the MRM images make them an ideal teaching aid that is suitable for students during the first years of a health-science degree, particularly medicine. As well as providing students with their first experience of MRM, these images allow students to access, at any time, all embryos used, to assess changes in the positions of different organs throughout their stages of development, and to acquire spatial vision, an absolute requirement in the study of human anatomy. We recommend that this technique be incorporated into the wealth of standard embryonic teaching methods already in use.     

Differential uptake of systemic fluorochrome Hoechst 33342 in lung and liver metastasis of B16 melanoma

Summary The growth and vascularization patterns of B16 melanoma colonies in the liver and lungs were measured and compared by histological techniques and dye diffusion patterns after injection of the fluorochrome Hoechst 33342. In the liver, the fluorescent pattern of dye diffusion revealed that uninodular tumours measuring up to 146 n in diameter were not functionally vascularized. However, when the nodules fused to give rise to multinodular tumours measuring between 256 and 366 n in diameter, a reticular dye diffusion pattern revealed functional tumour vascularization. In the lungs, subpleural, parenchymal and peritubular (i.e. surrounding blood vessels and airways) tumours were observed. The two former classes were vascularized down to thicknesses and diameters of 49 and 24 m respectively. In contrast, dye diffusion was never seen in peritubular tumour cuffs up to 609 m in thickness. The results indicate differences in vascularization patterns in B16 tumours in the liver and lungs, and differences between tumours growing in different sites within the lungs. If these results are applicable to metastases in these two organs, they indicate potential diffusion-mediated resistance to chemotherapy, and potential hypoxia-mediated resistance to radiotherapy of both metastases and micrometastases.     

Sequence of Echinochloa hoja blanca tenuivirus RNA-5

The sequence is presented of RNA-5 of Echinochloa hoja blanca tenuivirus, a second tenuivirus associated with rice cultivation in Latin America (after rice hoja blanca virus). The RNA is 1334 nucleotides long and contains in the complementary sense RNA a single long open reading frame. The deduced amino acid sequence of this open reading frame shows that it encodes a highly basic and hydrophilic 44 kD protein (pc5) with about 50% similarity to the pc5 protein of maize stripe virus (MStV). This and other features of the RNA are discussed.The GenBank accession number of the sequence reported in this paper is L47430.     

Stunning and myocardial contractile autoregulation studied on the isolated isovolumic blood-perfused dog heart

AIM: To study, for the first time, the effects of stunning on homeometric and heterometric autoregulation. METHODS AND RESULTS: Ischaemia (15 min)/reperfusion (30 min) was induced in the isovolumic blood-perfused dog heart preparation. Heart rate elevations (n = 9) from 60 to 200 beats min-1, in steps of 20 beats min-1, promoted the same inotropic stimulation in control (C) and stunning (S), indicating that ischaemia/reperfusion does not affect the changes in calcium kinetics elicited by the Bowditch effect. Sudden ventricular dilation (VD) (n = 10) evoked an instantaneous increase in developed pressure (Delta1DP) followed by a continuous slow performance increase (Delta2DP) in C and S. Delta1DP (C: 35 +/- 2.2 mmHg; S: 27 +/- 2.1 mmHg; P = 0.002) and Delta2DP (C: 20 +/- 1.6 mmHg; S: 14 +/- 1.3 mmHg; P = 0.002) decreased proportionally, while Delta2/Delta1DP (C: 0.57 +/- 0.13; S: 0.58 +/- 0.14) and slow response time course (T/2) were unchanged (C: 55 +/- 6.6 s; S: 57 +/- 7.7 s) after ischaemia/reperfusion. The reduction of Delta1DP can be understood as a decline of the myofilaments calcium responsiveness, the main pathophysiological effect of stunning. The reason for the weakening of Delta2DP, due to intracellular calcium gain, was not determined but it was supposed that its complete manifestation could be restricted by cyclic adenosine monophosphate (cAMP) myocardial content reduction. As reported by others, Delta2DP depends on myocardial cAMP, and it has been shown that myocardial cAMP is decreased after ischaemia/reperfusion. CONCLUSIONS: Contractile depression due to stunning has no effect on the inotropic stimulation generated by the Bowditch phenomenon. Immediate and time-dependent enhancements of contraction evoked by sudden VD are proportionally reduced and the slow response time course is unaffected in the stunned myocardium.     

Prevalence of obesity and hyperinsulinemia: its association with serum lipid and lipoprotein concentrations in healthy individuals from Maracaibo,Venezuela

The aim of this study was to analyse the prevalence of obesity and hyperinsulinemia and their association with lipid profile alterations on apparently healthy individuals from Maracaibo, Venezuela. We evaluated 306 men and 41 women, ages ranging from 33 to 65 years. All subjects underwent cardiovascular evaluation and laboratory examination after 10-12 h fasting, for glycaemia, total cholesterol, TG, VLDL-C, LDL-C and HDL-C as well as insulin. Seventy-four percent of men and 56.1% of women showed obesity (BMI > 25 Kg/m2). Men showed high concentrations of TG (48.3%), total cholesterol (40.2%), VLDL-C (48.3%) and LDL-C (33.9%) and low HDL-C levels (48%). The most frequent alteration on the lipid profile in women was high total cholesterol (46%) and LDL-C (51.2%). Men had significantly higher insulin concentrations than women (p < 0.005). After they were classified as obese or non obese, the obese subjects (men and women) showed higher prevalence of lipid profile alterations and insulin concentrations than non obese. The insulin concentration in obese men correlated with BMI, TG, VLDL-C and HDL and, in women with BMI, TG and VLDL-C. In conclusion, a high percentage of men and women in this study showed obesity and this obesity, specially in men, was strongly associated with lipid profile alterations and high insulin concentrations both well known cardiovascular risk factors.