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Biomedical subjects

J A Strong

Publications and source records attributed to J A Strong.

At least 37 records · Page 2Linked to original sources
PubMed1986

Multiple components of delayed potassium current in peptidergic neurons of Aplysia: modulation by an activator of adenylate cyclase.

The neurosecretory bag cell neurons of the mollusk, Aplysia, control egg-laying behavior in the animal. In these cells, elevation of cAMP greatly enhances the height and width of action potentials. A similar enhancement of action potentials is seen during the bag cell afterdischarge, a 30 min period of repetitive activity that may be triggered by peptides from the reproductive tract or by brief extracellular stimulation. The enhancement of action potentials during an afterdischarge is well correlated with the observed elevations of cAMP. In the present study, we have examined the effects of forskolin (an activator of adenylate cyclase) and theophylline (a phosphodiesterase inhibitor) on the delayed outward currents that are likely to control repolarization of the action potential. Isolated bag cell neurons, maintained in primary culture, were studied with a whole-cell patch clamp technique. High intracellular concentrations of EGTA were used to block potassium current activated by calcium entry. Analysis of the remaining voltage-dependent delayed outward current revealed two major components, which could be separated on the basis of their different kinetic properties. Both currents (IK1 and IK2) were carried by potassium. IK1, which did not inactivate during 100 msec depolarizations, was reduced in amplitude by application of forskolin and theophylline. Ik2, a current defined by its faster kinetic properties, partially inactivated during 100 msec depolarizations. This inactivation was markedly speeded by application of forskolin and theophylline. It is suggested that such changes in outward current in response to cAMP could explain the enhancement of spike width seen during an afterdischarge in vivo.

Action Potentials↗
PubMed1984

Modulation of potassium current kinetics in bag cell neurons of Aplysia by an activator of adenylate cyclase.

The bag cell neurons of Aplysia are neurosecretory cells which control egg-laying behavior. In their resting state, the cells have a high resting potential and show no spontaneous activity. In response to brief stimulation of a neural input, the cells depolarize and fire repetitively for up to 60 min. This afterdischarge is thought to be controlled by elevations of intracellular adenosine 3':5'-monophosphate (cAMP). A voltage clamp study of bag cells in primary culture was undertaken in order to characterize the effects of cAMP on the cells' electrical properties. The transient outward potassium current (A-current) was studied before and after the application of forskolin (an activator of adenylate cyclase) and RO20-1724 (a phosphodiesterase inhibitor). These drugs reduced the amplitude of the A-current, primarily by speeding the inactivation process. The time constants for inactivation were speeded at all potentials, but the largest effects were seen at the more positive potentials (-40 to -15 mV), where the time constants were reduced 5-fold. Neither the activation process nor the steady-state parameters of inactivation were altered by the drugs. It is suggested that these changes in the A-current could explain the ability of the bag cells to fire repetitively during the afterdischarge.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗
PubMed1982

Total body neutron activation analysis of calcium: calibration and normalisation.

An irradiation system has been designed, using a neutron beam from a cyclotron, which optimises the uniformity of activation of calcium. Induced activity is measured in a scanning, shadow-shield whole-body counter. Calibration has been effected and reproducibility assessed with three different types of phantom. Corrections were derived for variations in body height, depth and fat thickness. The coefficient of variation for repeated measurements of an anthropomorphic phantom was 1.8% for an absorbed dose equivalent of 13 mSv (1.3 rem). Measurements of total body calcium in 40 normal adults were used to derive normalisation factors which predict the normal calcium in a subject of given size and age. The coefficient of variation of normalised calcium was 6.2% in men and 6.6% in women, with the demonstration of an annual loss of 1.5% after the menopause. The narrow range should make single measurements useful for diagnostic purposes.

Adult↗
PubMed1979

Familial pseudohyperkalaemia. A new syndrome.

Inherited pseudohyperkalaemia due to an abnormal red-blood-cell potassium leak was discovered in 16 of 28 relatives of a woman with pseudohyperkalaemia. Autosomal dominance seemed to account for inheritance of this abnormality. Affected subjects were not anaemic and had normal in-vivo plasma-potassium concentrations.

Adult↗
PubMed1979

The initiation of excitation and light adaptation in Limulus ventral photoreceptors.

Two types of experiments indicate that light adaptation and excitation are initiated by the same, rather than different, populations of visual pigment. (a) The criterion action spectra of light adaptation and excitation are the same. (b) Increment-threshold curves were measured with a voltage-clamp technique under conditions of high and low concentration of plasma membrane rhodopsin (Rhpm). SD, the dark-adapted sensitivity, and 1/I2, the inverse of the background irradiance that desensitized by 0.3 log units, underwent the same fractional change when the rhodopsin concentration was changed. Both quantities appear to be linearly related to Rhpm. Reversible reductions in Rhpm were achieved by orange irradiation during a brief increase of extracellular pH from 7.8 to 10. This procedure would be unlikely to produce similar concentration changes in a hypothetical intracellular pigment because the concurrent change in intracellular pH, measured using the dye, phenol red, was only 0.45 pH units. It is thus unlikely that an intracellular pigment initiates light adaptation. On the assumption that light adaptation is mediated by a light-induced release of Ca++ from an intracellular store. the results reported here imply that an intracellular transmitter is needed to couple Rhpm to the intracellular store.

Adaptation, Physiological↗
PubMed1978

Hypothalmic-pituitary adrenal responsiveness to dexamethasone-insulin tolerance test in acromegalic patients before and during treatment with bromocriptine.

Insulin tolerance tests were carried out in 10 acromegalic patients after 1 mg dexamethasone had been given the previous evening (DEX-ITT). Nine patients showed a rise in plasma 11-OHCS and four patients showed a rise in plasma growth hormone (GH) levels. These responses were unaltered after treatment with bromocriptine 10 mg daily for two months. Basal plasma GH levels fell in 6 of the patients and the mean plasma GH levels of the 10 patients during an oral glucose tolerance test (OGTT) fell from 63.2 +/- 25.5 ng/ml before treatment to 53.0 +/- 27.1 ng/ml (mean +/- sem; p less than 0.05). These data fail to confirm a previous report of abnormal hypothalmic-pituitary-adrenal suppressibility during a DEX-ITT in acromegalic patients. They also indicate that bromcriptine does not alter the responses of plasma 11-OHCS and plasma GH to the DEX-ITT despite lowering plasma GH levels.

11-Hydroxycorticosteroids↗
PubMed1977

Growth hormone, insulin, and prolactin secretion in anorexia nervosa and obesity during bromocriptine treatment.

We studied secretion of growth hormone (GH), insulin, and prolactin in eight women with anorexia nervosa and nine women with refractory obesity before and during treatment with bromocriptine, 10 mg/day. In the anorexic patients the raised plasma GH concentrations occurring during an oral glucose tolerance test fell significantly while on bromocriptine treatment, but there was no change in plasma insulin or blood glucose concentrations. In the obese patients, however, plasma GH concentrations remained low during the oral glucose tolerance test, and were not modified by bromocriptine. Blood glucose and plasma insulin concentrations were also unchanged. Plasma GH and plasma 11-hydroxycorticosteroid responses to insulin-induced hypoglycaemia were unaffected. Serum prolactin concentrations which were raised in five anorexic patients and marginally raised in two obese subjects, fell significantly in both groups during treatment. We observed no consistent weight changes in either groups.

Adolescent↗
PubMed1977

The relationship between thyroid function and the renal response to parathyroid hormone.

The effect of thyroid status on renal adenosine 3', 5'-cyclic monophosphate (cyclic AMP) metabolism was assessed by measuring the increase in plasma cyclic AMP concentration following the intravenous administration of parathyroid hormone (PTH) to five hypothyroid and six hyperthyroid patients and seven euthyroid control subjects. PTH caused a rapid, transient increase in the concentration of plasma cyclic AMP which was similar in magnitude and time course in the euthyroid and hyperthyroid groups, but reduced in magnitude in the hypothyroid patients. The magnitude of the plasma cyclic AMP response to PTH was positively related to the free thyroxine index. The results suggest that the development of hypothyroidism may impair the renal response to PTH by affecting the turnover of cyclic AMP in the renal cortex.

Cyclic AMP↗
PubMed1977

Thyroxine and triiodothyronine levels in hyperthyroid patients during treatment with propranolol.

Serum triiodothyronine (T3) and thyroxine (T4) levels were measured in twelve hyperthyroid patients before and after treatment with propranolol, 40 mg four times daily, for 2 weeks. There was a significant fall in serum T3 and a significant rise in serum T4 concentrations in the group as a whole and it was concluded that the clinical effectiveness of propranolol in hyperthyroidism may be mediated in part by its action on the peripheral metabolism of thyroid hormones. Propranolol treatment should be withdrawn gradually as removal of the suppressive action of the drug on thyroid hormone metabolism is potentially hazardous, particularly in patients with ischaemic heart disease.

Adult↗