Relationship between photoperiod, plasma concentration of ionic calcium and the histology of the prolactin-secreting cells of the rostral pars distalis of the pituitary gland, the corpuscles of stannius and the ultimobranchial gland in the goldfish, Carassius auratus L. /

The relationship between photoperiod, plasma concentration of ionic calcium and the histology of the prolactin-secreting cells of the rostral pars distalis of the pituitary gland, the Corpuscles of Stannius and the Ultimobranchial gland were investigated. Neither the plasma concentration of ionic calcium nor histologically apparent prolactin cell activity could be correlated with photoperiod. Some evidence of a photoperiodic effect on both the Corpuscles of Stannius and the Ultimobranchial gland was obtained. The expected reciprocal relationship between the activity of these glands was not obvious at the histological level . Quantitative and qualitative analysis at the light microscope level revealed, however, that the hormone prolactin-secreting eta cells of the rostral pars distalis and the hypocalcin-secreting cells of the Corpuscles of Stannius may be arranged in a lamellar pattern comprized of synchronous bands of cells in like-phase of a secretory cycle consisting of four stages - synthesis, storage, release and reorganization. Such synchronized cell cycles in these glands have not heretofore been described in literature. It is suggested that the maintenance of at least 255? of the cells in any one phase of the cycle ensures a supply of the required hormone at all times.

A possible role for intrinsic calcium buffers in the long- term adaptation of crayfish neurons

Increasing the impulse activity of neurons in vivo over 3 or more days causes a reduction in transmitter release that persists for days or weeks (eg. Mercier and Atwood, 1989). This effect is usually accompanied by decreased synaptic fatigue. These two changes involve presynaptic mechanisms and indicate "long-term adaptation" (LTA) of nerve terminals. Previous experiments have shown that LTA requires extracellular calcium and protein synthesis (eg. Hong and Lnenicka, Soc. Neurosci. Abstr. 17:1322) and appears to involve communication between the cell body and the nerve terminals. The present study examines the possibility that the reduction in transmitter release is caused by an -increase in the calcium buffering ability within the nerve terminals. It examines the responses of adapted and control nerve terminals to exogenously applied calcium buffer, BAPTA-AM, which decreases transmitter release (Robitialle and Charlton, 1992). If LTA increases intrinsic Ca2+-buffering, the membrane permeant form of BAPTA should have less effect on adapted nerve terminals than on controls. Experiments are performed on the phasic abdominal extensor motor neurons of the crayfish, Procambarns clarkii. BAPTA-AM decreases excitatory postsynaptic potentials (EPSP's) of the phasic extensor muscles in a dosedependent manner between 5 and 50 JLM. LTA is elicited by in vivo stimulation at 2.5 Hz for 2-4 h per day over 3 days, which reduces EPSP's by over 50%. Experiments indicate that BAPTA-AM produces no significant change in EPSP reduction in adapted neurons when compared to controls. These results do not support the hypothesis that increased daily activity alters rapid intrinsic calcium buffers, that are able to reduce transmitter output in the same manner as BAPTA.

Cytosolic calcium levels and stress induced y-amino butyrate synthesis in asparagus mesophyll cells

Numerous investigations have demonstrated large increases in y-amino butyrate (GABA) levels in response to a variety of stresses such as touch or cold shock (Wallace et ale 1984) Circumstantial evidence indicating a role of Ca2 + in these increases includes elevated Ca2+ levels in response to touch and cold shock (Knight et ale 1991), and the demonstration of a calmodulin binding domain on glutamate decarboxylase (GAD), the enzyme responsible for GABA synthesis (Baum et al 1993) In the present study the possible role of Ca2+ and calmodulin in stimulation of GAD and subsequent GABA accumulation was examined using asparagus mesophyll cells. Images of cells loaded with the Ca2+ indicator Fluo-3 revealed a rapid and transient increase in cytosolic Ca2+ in response to cold shock. GABA levels increased by 106% within 15 min. of cold shock. This increase was inhibited 70% by the calmodulin antagonist W7, and 42% by the Ca2+ channel blocker La3+.. Artificial elevation of intracellular Ca2+ by the Ca2+ionophore A23187 resulted in an 61% increase in GABA levels. Stimulation of GABA synthesis by ABA resulted in an 83% increase in GABA levels which was inhibited 55% by W7. These results support the hypothesis that cold shock stimulates Ca2+ entry into the cytosol of the cells which results in Ca2+/calmodulin mediated activation of GAD and consequent GABA synthesis.

Polytypism and Silicon carbide : a solid state nuclear magnetic resonance study

A survey of predominantly industrial silicon carbide has been carried out using Magic Angle Spinning nuclear magnetic resonance (MAS nmr); a solid state technique. Three silicon carbide polytypes were studied; 3C, 6H, and 15R. The 13C and 29 Si MAS nmr spectra of the bulk SiC sample was identified on the basis of silicon (carbon) site type in the d iff ere n t pol Y t Y pes • Out to 5.00 A fro mac en t r a lsi 1 i con (0 r carbon) atom four types of sites were characterized using symmetry based calculations. This method of polytype analysis was also considered, in the prelminary stages, for applications with other polytypic material; CdBr 2 , CdI 2 , and PbI 2 " In an attempt to understand the minor components of silicon carbide, such as its surface, some samples were hydrofluoric acid washed and heated to extreme temperatures. Basically, an HF removable species which absorbs at -110 ppm (Si0 2 ) in the 29 Si MAS nmr spectrum is found in silicon carbide after heating. Other unidentified peaks observed at short recycle delays in some 29 Si MAS nmr spectra are considered to be impurities that may be within the lattice. These components comprise less than 5% of the observable silicon. A Tl study was carried out for 29 Si nuclei in a 3C ii polytype sample, using the Driven Equilibrium Single-Pulse Observation of T1 (DESPOT) technique. It appears as though there are a number of nuclei that have the same chemical shift but different T1 relaxation times. The T1 values range from 30 seconds to 11 minutes. Caution has to be kept when interpreting these results because this is the first time that DESPOT has been used for solid samples and it is not likely in full working order. MAS nmr indicates that the 13C and 29 Si ~sotropic chemical shifts of silicon carbide appear to have a reciprocal type of relationship_ Single crystal nmr analysis of a 6H sample is accordance with this finding when only the resultant isotropic shift is considered. However, single crystal nmr also shows that the actual response of the silicon and carbon nuclear environment to the applied magnetic field at various angles is not at all reciprocal. Such results show that much more single crystal nmr work is required to determine the actual behavior of the local magnetic environment of the SiC nuclei.

The Role of Membrane Lipid Composition on Sarco(endo)plasmic Reticulum Calcium ATPase Function in Rat Soleus Muscle

Sarco(endo)plasmic reticulum calcium ATPase (SERCA) is a transmembrane protein whose function is regulated by its immediate lipid environment (annulus). The composition of the annulus is currently unknown or it’s susceptibility to a high saturated fat diet (HSFD). Furthermore it is uncertain if HSFD can protect SERCA from thermal stress. The purpose of the study was to determine SERCA annular lipid composition, resulting impact of a HSFD, and in turn, influence on SERCA activity with and without thermal stress. The major findings were annular lipids were shorter and more saturated compared to whole homogenate and HSFD had no effect on annular lipid composition or SERCA activity with and without thermal stress. Both average chain length and unsaturation index were positively correlated with SERCA activity with and without thermal stress. These findings suggest that annular lipid composition is different than whole homogenate and its composition appears to be related to SERCA function.