Search PubMed⌕ Search

Biomedical subjects

H Gainer

Publications and source records attributed to H Gainer.

189 records · Page 11Linked to original sources
PubMed1968

The role of calcium in excitation-contraction coupling of lobster muscle.

Potassium contractures were induced in lobster muscle bundles under conditions which produced varying KCl fluxes into the fibers. The presence or absence of chloride fluxes during depolarization by high concentrations of potassium, had no effect on the tensions developed. The curve relating tension to the membrane potential had a typical sigmoid shape with an apparent "threshold" for tension at -60 mv. Soaking the muscles in low (0.1 mM) calcium salines for 30 min completely eliminated the potassium contractures but the caffeine contractures were only slightly reduced under these conditions. The potassium contracture could be completely restored in less than 2 min by return of the calcium ions to the saline. Evidence is presented for independent, superficial, and deep calcium sites; the superficial sites appear to be involved in the coupling mechanisms associated with potassium contractures. These sites are highly selective for Ca(++), and attempts to substitute either Cd(++), Co(++), Mg(++), Ba(++), or Sr(++) for Ca(++) were unsuccessful. However, K(+) appeared to compete with Ca(++) for these sites, and the evoked tension could be reduced by prestimulation of the muscle fibers with high K(+) salines. The results of studies on the influx of (45)Ca during potassium contractures were compatible with the view of muscle activation by the entry of extracellular calcium.

Animals↗
PubMedDate not supplied

Vasopressin administration to neonatal rats reduces antidiuretic response in adult kidneys.

Neonatal rats who had been given injections of vasopressin on days 1-7 after birth exhibited polyuria as adults. In vivo antidiuresis bioassays demonstrated that their kidneys were deficient in their ability to concentrate urine in response to stimulation with vasopressin. The kidneys also showed a reduction in vasopressin-induced cyclic AMP production, although parathyroid hormone- and calcitonin-induced levels were normal. This suggests a specific deficit in vasopressin receptor-adenylate cyclase function. In contrast, the neonatal treatment had no effect on the sensitivity of the adult vasculature to the hypertensive effects of vasopressin. These results show that short exposures to high levels of vasopressin early in development can produce a long-term defect in vasopressin responsiveness that is specific to the kidney.

Animals↗
PubMedDate not supplied

Immunocytochemical identification of dynorphin-containing vesicles in Brattleboro rats.

Vasopressin and its carrier protein, vasopressin-associated neurophysin, are co-packaged together with an opioid peptide, dynorphin, into 160 nm diameter neurosecretory vesicles in the normal rat hypothalamo-neurohypophysial system. The homozygous Brattleboro rat lacks vasopressin and vasopressin-associated neurophysin, but contains substantial amounts of dynorphin in the vasopressin-deficient neurosecretory cells. We used post-embedding electron microscopic immunocytochemistry to determine the subcellular location of dynorphin in Brattleboro rats. The results show that dynorphin is present within 100 nm neurosecretory vesicles in homozygous Brattleboro cell bodies and axons, and within 160 nm vesicles in heterozygous (control) neurosecretory cell bodies and axons. Oxytocin-associated neurophysin is present in a separate population of magnocellular neurons in both homozygous and heterozygous rats, and is contained within 160 nm vesicles in both cases. Therefore, the absence of synthesis of the vasopressin prohormone results in a dramatic reduction of neurosecretory vesicle size, despite the continued synthesis and packaging of dynorphin peptides.

Animals↗
PubMedDate not supplied

An immunochemical analysis of oxytocin and vasopressin prohormone processing in vivo.

Antisera against partially processed, unamidated forms of AVP and OT were raised and characterized by radioimmunoassay and immunocytochemistry. These antibodies, and antibodies that recognize fully processed, amidated forms of AVP and OT, were used together with various fractionation methods to study the content of prohormones, partially processed and fully processed forms of AVP and OT in the hypothalamo-neurohypophysial system of adult and fetal (E21) rats. The levels of cleaved AVP and OT in the fetus were lower than those of the adult (1 to 3 orders of magnitude for brain and pituitary, respectively), and the detection of cleaved OT in brain and pituitary was delayed compared to that of AVP. Pro-AVP cleavage efficiency in the adult and the fetus was high (99 and 95% cleavage, respectively) resulting in formation of fully processed amidated forms of AVP, with no detectable partially processed peptides. Pro-OT processing in the adult was very similar (over 99% cleavage) resulting in formation of fully processed amidated OT. However, Pro-OT processing efficiency in the fetus was very low and incomplete, resulting in 40% unprocessed precursor and the accumulation of C-terminally extended unamidated intermediate forms (OT-Gly, OT-Gly-Lys, and OT-Gly-Lys-Arg).

Animals↗
PubMedDate not supplied

Slice cultures of LHRH neurons in the presence and absence of brainstem and pituitary.

Luteinizing hormone releasing hormone (LHRH) neurons from the preoptic area (POA)/hypothalamus of the postnatal rat were cultured for up to 7 weeks using a slice explant roller culture technique. The slices thinned to quasi-monolayers, but maintained organotypic distributions of large numbers of immunocytochemically identifiable LHRH, neurotensin, tyrosine hydroxylase, neurophysin and corticotropin releasing hormone-containing neurons. The distribution, survival and morphology of LHRH cells in co-cultures with brainstem and anterior pituitary was quantitated, and found to be similar to that observed in single cultures. LHRH fibers grew into either pituitary or brainstem tissue, however when all three tissues were co-cultured, LHRH fibers preferentially invaded the pituitary. LH immunoreactive anterior pituitary gonadotropes were maintained only in co-cultures containing POA/hypothalamic slices, and addition of an LHRH antagonist in such cultures, inhibited LH immunoreactivity in the gonadotropes. This slice explant roller culture method effectively maintains the cyto- and chemoarchitecture and functional properties of the LHRH system for long periods in vitro and should provide excellent models for studying the interactive and molecular characteristics of postnatal LHRH neurons.

Animals↗
PubMedDate not supplied

Optical recording of action potentials from vertebrate nerve terminals using potentiometric probes provides evidence for sodium and calcium components.

Optical methods are shown to monitor action potentials from a population of nerve terminals in the neurohypophysis of Xenopus. Calcium antagonists such as cadmium and nickel ions block a component of the action potential that probably reflects a calcium-mediated potassium conductance, and tetrodotoxin blocks an inward sodium current, revealing a calcium component to the action potential upstroke.

Action Potentials↗
PubMedDate not supplied

Co-localization of corticotropin-releasing factor and vasopressin in median eminence neurosecretory vesicles.

Vasopressin (VP) potentiates the effect of corticotropin-releasing factor (CRF) on the secretion of adrenocorticotropic hormone (ACTH) from anterior pituitary cells in vitro, and both CRF and VP have been found in portal blood. These data support the hypothesis that VP acts synergistically with CRF to cause the secretion of ACTH in vivo but the origin of the CRF and VP, and the physiology of their release, have not been precisely defined. Parvocellular cell bodies in the paraventricular nucleus (PVN) which project to the external zone of the median eminence can be stained for both CRF and VP after adrenalectomy, and there is light microscopic immunocytochemical evidence that neurophysin (NP) may be located within some of the CRF-containing axons. Electron microscopic immunocytochemical studies have demonstrated the presence of CRF, VP and its 'carrier' protein, VP-associated neurophysin (NP-VP) in 100-nm neurosecretory vesicles (NSVs) in axons terminating near the portal capillary plexus in the external zone of the median eminence. If these peptides are extensively co-localized in the same NSVs in the median eminence, then coordinate secretion of CRF and VP in vivo is obligatory, at least in some physiological circumstances. We demonstrate in this report, using post-embedding electron microscopic immunocytochemistry on serial ultrathin sections, that CRF, VP and NP-VP are contained not only in the same axons and terminals, but in the same 100-nm NSVs in the median eminence of both normal and adrenalectomized rats. In addition, in the normal rat median eminence 44% of the CRF-positive axons and terminals stained strongly for VP and NP-VP, whereas in the adrenalectomized rat virtually all the CRF-positive structures in the median eminence showed strong staining for VP and NP-VP, indicating a transformation of one subpopulation of CRF-positive axons and terminals by adrenalectomy.

Adrenalectomy↗