Chemical composition and biomass of Coscinodiscus asteromphalus in Jiaozhou Bay, China.

The large diatom Coscinodiscus asteromphalus was separated from seawater in Jiaozhou Bay using a repeated precipitation method and then its chemical compositions of carbon (C), nitrogen (N), phosphorus (P), and silicon (Si) combined with chlorophyll a (Chl a) were examined for the first time for a natural population in this study. Results show that the contents of carbon, nitrogen, phosphorus, silicon, and Chl a in C. asteromphalus cells were 35,610.5, 9374.2, 352.4, 1105.5, and 1767.0 pg/cell, respectively, and the corresponding molar ratios of C/N, N/P, Si/P, and Si/N in C. asteromphalus cells were 4.5, 66.0, 2.7, and 0.07, respectively, which are different from the Redfield ratio. Additionally, their C/Chl a mass ratio was 23.2. High N/P ratio and low Si/P and Si/N ratios in C. asteromphalus cells were consistent with those in particulates of any size and seawater in the bay, reflecting an ecological response of phytoplankton to the nutrient structure of seawater, suggesting Si limitation to phytoplankton growth. The fact that C. asteromphalus spread all over the bay mainly in summer and autumn and the fact that Chl a content in C. asteromphalus cells could account for a maximum percentage of 78% of those in the water column suggest that the contribution of C. asteromphalus to phytoplankton biomass was significant in Jiaozhou Bay.

Adenosine A2 receptors are involved in the activation of ATP-sensitive K+ currents during metabolic inhibition in guinea pig ventricular myocytes.

It has been hypothesized that an interaction among adenosine A(1) receptors, protein kinase C (PKC) activation, and ATP-sensitive potassium channels (K(ATP)) mediates ischemic preconditioning in experiments on different animal species. The purpose of this study was to determine if activation of K(ATP) is functionally coupled to A(1) receptors and (or) PKC activation during metabolic inhibition (MI) in guinea pig ventricular myocytes. Perforated-patch using nystatin and conventional whole-cell recording methods were used to observe the effects of adenosine and adenosine-receptor antagonists on the activation of K(ATP) currents during MI induced by application of 2,4-dinitrophenol (DNP) and 2-deoxyglucose (2DG) without glucose, in the presence or absence of a PKC activator, phorbol 12-myristate 13-acetate (PMA). Adenosine accelerated the time course activation of K(ATP) currents during MI under the intact intracellular condition or dialyzed condition with l mmol/L ATP in the pipette solution. The accelerated effect of adenosine activation of K(ATP) under MI was not reversed by a nonselective Al adenosine receptor antagonist, 8-(p-sulfophenyl)theophylline (SPT), or a specific Al adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). However, the adenosine A(2) receptor antagonist alloxazine reversed the time course activation of the K(ATP) current under MI. An adenylate cyclase activator, forskolin, did not further abbreviate the time course activation of K(ATP) with or without adenosine. Application of a PKC blocker, chelerythrine, reversed the time course activation of K(ATP) by adenosine under MI. In addition, pretreatment with a PKC activator, PMA, had similar effects to adenosine, while adenosine did not further shorten the time required for activation of K(ATP) currents during MI with PMA pretreatment. There is no direct evidence of activation of K(ATP) currents by adenosine A(1) receptor during metabolic inhibition under our experimental condition. However, adenosine A(2) receptor activation is involved in the K(ATP) channel activation in the guinea pig ventricular myocytes, of which effect is not mediated through the increase in intracellular cAMP. Adenosine seems to interact with PKC activation to open K(ATP) during MI, but a possible link between the adenosine A(2) receptor and PKC activation in this process needs further elucidation.

Regulation of intrinsic excitability in hippocampal neurons by activity-dependent modulation of the KV2.1 potassium channel.

KV2.1 is the prominent somatodendritic sustained or delayed rectifier voltage-gated potassium (KV) channel in mammalian central neurons, and is a target for activity-dependent modulation via calcineurin-dependent dephosphorylation. Using hanatoxin-mediated block of KV2.1 we show that, in cultured rat hippocampal neurons, glutamate stimulation leads to significant hyperpolarizing shifts in the voltage-dependent activation and inactivation gating properties of the KV2.1-component of delayed rectifier K+ (IK) currents. In computer models of hippocampal neurons, these glutamate- stimulated shifts in the gating of the KV2.1-component of IK lead to a dramatic suppression of action potential firing frequency. Current-clamp experiments in cultured rat hippocampal neurons showed glutamate stimulation induced a similar suppression of neuronal firing frequency. Membrane depolarization also resulted in similar hyperpolarizing shifts in the voltage-dependent gating properties of neuronal IK currents, and suppression of neuronal firing. The glutamate-induced effects on neuronal firing were eliminated by hanatoxin, but not by dendrotoxin-K, a blocker of KV1.1-containing channels. These studies together demonstrate a specific contribution of modulation of KV2.1 channels in the activity-dependent regulation of intrinsic neuronal excitability.

[Chlorophyll-a concentration and phytoplankton size-fractionated composition in Jiaozhou Bay].

An investigation was made on the chlorophyll-a (Chla) concentration and phytoplankton size-fractionated composition in Jiaozhou Bay and its adjacent waters in February, May, August, and November 2008. The average annual Chla concentrations inside and outside the Bay was 4.90 mg x m(-3) and 2.03 mg x m(-3), respectively. The Chla concentration presented a decreasing trend from the northeast and near-shore to the central, south, and outside of the Bay, and had an obvious double-peak seasonal variation, being higher in summer and winter. The phytoplankton in the Bay was dominated by nanophytoplankton, accounting for 60.9% of the total Chla concentration, followed by microphytoplankton, and picophytoplankton, which was consistent with the phytoplankton size-fractionated composition in coastal waters of China. Comparing with historical data, the proportion of nanophytoplankton in the Bay had some increase, while that of picophytoplankton decreased to some extent.