Active zone assembly and synaptic release.

Neurotransmitter release at chemical synapses occurs when synaptic vesicles fuse to the presynaptic membrane at a specialized site termed the active zone. The depolarization-induced fusion is highly dependent on calcium ions, and, correspondingly, the transmission characteristics of synapses are thought to be influenced by the spatial arrangement of voltage-gated calcium channels with respect to vesicle release sites. Here, we review the involvement of the Drosophila Bruchpilot (BRP) protein in active zone assembly, a process that is required for the clustering of presynaptic calcium channels to ensure efficient vesicle release.

Quartz glass pipette puller operating with a regulated oxy-hydrogen burner.

Quartz glass electrodes are superior to conventional glass electrodes for low-noise recording. They have better electrical characteristics and hydrophobic surfaces which resist creeping of salt solutions. We used oxy-hydrogen heating with program-controlled gas pressure to melt quartz glass capillaries. Usually, the relative wall thickness (the quotient of the outer and inner diameters do/di) of capillaries is, at best, maintained up to the electrode tip. If tips with thicker walls can be produced, coating and other surface treatments can be avoided. We found that programmed heating periods without pull allowed an fivefold increase of do/di in the tip region. Since do/di is inversely proportional to input capacity, the recording noise was minimized and became insignificant relative to amplifier and holder noise. A sample patch-clamp recording is shown.

Opioidergic modulation of voltage-activated K+ currents in magnocellular neurons of the supraoptic nucleus in rat.

Opioidergic modulation plays an important role in the control of oxytocin and vasopressin release by magnocellular neurons (MCNs) in the supraoptic and paraventricular nuclei of the hypothalamus. We have used whole cell patch-clamp recording in acute slices of the supraoptic nucleus (SON) of the hypothalamus to study opioidergic modulation of voltage-dependent K+ currents in MCNs that are involved in release activity. The mu-receptor agonist D-Ala2, N-Me-Phe4, Gly5-ol-enkephalin (DAMGO, 2 microM) affected K+ currents in 55% of magnocellular neurons recorded from. In these putative oxytocinergic cells, DAMGO increased the delayed rectifier current (IK(V)) amplitude by approximately 50% without significant effects on its activation kinetics. The transient A current (IA) was enhanced by DAMGO by approximately 36%. Its inactivation kinetic was accelerated slightly while the voltage dependence of steady-state inactivation was shifted by -6 mV to more negative potentials. All DAMGO effects were blocked by the preferential non-kappa-opioid antagonist naloxone (10 microM). The kappa-opioid agonist trans-(+/-)-3, 4-dichloro-N-methyl-N(2-[1-pyrrolidinyl]cyclohexyl)benzeneacetamide (U50,488; 10 microM) strongly suppressed IK(V) by approximately 57% and evoked a 20-mV hyperpolarizing shift and an acceleration of activation in both, DAMGO-sensitive and -insensitive putative vasopressinergic MCNs. U50,488 reduced IA by approximately 29% and tau of inactivation by -20% in DAMGO-sensitive cells. In contrast, in DAMGO-insensitive cells U50,488 increased IA by approximately 23% and strongly accelerated inactivation (tau -44%). The effects of U50,488 were suppressed by the selective kappa-receptor antagonist nor-binaltorphimine (5 microM). We conclude that mu- and kappa-opioidergic inputs decrease and increase excitability of oxytocinergic MCNs, respectively, through modulation of voltage-dependent K+ currents. In vasopressinergic MCNs, kappa-opioidergic inputs differentially modulate these K+ currents. The modulation of K+ currents is assumed to significantly contribute to opioidergic control of hormone release by MCNs within the supraoptic nucleus and from the axon terminals in the neural lobe.

A new type of Ca-channel modulation by a novel class of 1,4-dihydropyridines.

Both Ca-antagonistic as well as Ca-agonistic 1,4-dihydropyridines (DHPs) have become extremely important tools to investigate the role of Ca-channels under various physiological and pathophysiological conditions. While Ca-antagonists stabilize the inactivated state of the Ca-channel without influencing the voltage dependent open and closed times, Ca-agonists prolong the mean open time of the channel. We here report for the first time the effects of a novel DHP, BAY Y 5959, which modulates Ca-channel gating in a unique manner: It increases both the mean open time and the mean closed time of the Ca-channel by binding to the DHP receptor. This results in a reduced rate of Ca-current activation, an increased peak current, and a strongly prolonged tail current decay. All these effects are strongly voltage dependent. Therefore it depends on resting membrane potential and shape of the action potential whether and how the Ca-influx into the cell is influenced. This novel mode of action of BAY Y 5959 results in an interesting pharmacological profile: It has a strong positive inotropic effect in the heart without influencing vessel tone. Therefore the term Ca-promoter is suggested; it could become a new approach for the drug treatment of congestive heart failure.