Quantal transmitter secretion from myocytes loaded with acetylcholine.

It is well known that transmitter secretion requires specialized secretory organelles, the synaptic vesicles, for the packaging, storage and exocytotic release of the transmitter. Here we report that when acetylcholine (ACh) is loaded into an isolated Xenopus myocyte, there is spontaneous quantal release of ACh from the myocyte which results in activation of its own surface ACh channels and the appearance of membrane currents resembling miniature endplate currents. This myocyte secretion probably reflects Ca(2+)-regulated exocytosis of ACh-filled cytoplasmic compartments. Furthermore, step depolarization of the myocyte membrane triggers evoked ACh release from the myocyte with a weak excitation-secretion coupling. These findings suggest that quantal transmitter secretion does not require secretory pathways unique to neurons and that the essence of presynaptic differentiation may reside in the provision of transmitter supply and modification of the preexisting secretion pathway.     

Human cytomegalovirus UL97 open reading frame encodes a protein that phosphorylates the antiviral nucleoside analogue ganciclovir.

Human cytomegalovirus (HCMV, a betaherpes virus) is the cause of serious disease in immunologically compromised individuals, including those with acquired immunodeficiency syndrome. One of the compounds used in the chemotherapy of HCMV infections is the nucleoside analogue 9-(1,3-dihydroxy-2-propoxymethyl)-guanine (ganciclovir). The mechanism of action of this drug is dependent on the formation of the nucleoside triphosphate, which is a strong inhibitor of the viral DNA polymerase. Thymidine kinase, which is encoded by many of the herpesviruses, catalyses the initial phosphorylation of ganciclovir. But there is no evidence for the coding of this enzyme by HCMV, and DNA sequence analysis of the HCMV genome has shown that there is no open reading frame characteristic of a herpesvirus thymidine kinase. Here we present biochemical and immunological evidence that the HCMV UL97 open reading frame codes for a protein capable of phosphorylating ganciclovir. This protein seems to be responsible for the selectivity of ganciclovir and will be useful tool in the understanding and refinement of the antiviral activity of new selective anti-HCMV compounds.     

Effect of volatile anesthetics on the circular dichroism of bilirubin bound to human serum albumin

The characteristic circular dichroism of bilirubin bound to human serum albumin undergoes a remarkable sign inversion on addition of halothane, chloroform and other volatile anesthetics. This sign inversion, which is completely reversed by removal of the anesthetic, reflects a pronounced conformational change of the bound ligand; probably a complete inversion of chirality. The observation suggests that association of volatile anesthetics with proteins can markedly alter the internal topography of receptor sites and potentially influence the stereoselectivity of ligand binding.     

Nuclear localization and signalling activity of phosphoinositidase C beta in Swiss 3T3 cells.

The hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) is a widespread receptor-coupled signalling system at the plasma membrane of most eukaryotic cells. The existence of an entirely separate nuclear phosphoinositide signalling system is suggested from evidence that purified nuclei synthesize PtdInsP2 and phosphatidylinositol 4-phosphate (PtdInsP) in vitro and that a transient decrease in the mass of these lipids occurs when Swiss 3T3 cells are cultured in the presence of insulin-like growth factor-1 (IGF-1). These IGF-1-dependent changes in inositol lipids coincide with an increase in nuclear diacyglycerol and precede translocation to the nucleus and activation of protein kinase C (refs 5, 6). Circumstantial evidence that links these changes with mitosis comes from the isolation of a 3T3 clone that expresses the type-1 IGF receptor and binds IGF-1 peptide but does not respond mitogenically or show transient mass changes in nuclear inositol lipids. A key question is how IGF-1 initiates the rapid breakdown of PtdInsP and PtdInsP2 in the nucleus. Here we present evidence that nuclei of 3T3 cells contain the beta-isozyme of phosphoinositidase C, whereas the gamma-isozyme is confined to the cytoplasm and that IGF-1 treatment stimulates exclusively the activity of nuclear phosphoinositidase C.     

Seasonality in human sleep.

The timing of sleep and sleep EEG parameters in 10 healthy male subjects were investigated in four seasons under controlled conditions. The phase of nocturnal sleep was delayed about one and a half hours in winter as compared to that in summer. The duration of stage 4 sleep decreased and REM sleep increased significantly in winter compared with summer. The seasonality in the timing of sleep can be explained by photoperiodic time cues, but the changes in sleep EEG parameters are difficult to explain in terms of photoperiod.     

Making light work with optical tweezers.

Microscopic objects, including biological material, can be remotely manipulated with tightly focused beams of infrared laser light. The use of optical traps, or 'optical tweezers', holds great promise for noninvasive micromanipulation and mechanical measurement in cell biology. Optical tweezers are the 'tractor beams' of today's technology.     

Periodic paralysis in quarter horses: a sodium channel mutation disseminated by selective breeding.

We recently reported on a linkage study within a Quarter Horse lineage segregating hyperkalaemic periodic paralysis (HYPP), an autosomal dominant condition showing potassium-induced attacks of skeletal muscle paralysis. HYPP co-segregated with the equine adult skeletal muscle sodium channel alpha subunit gene, the same gene that causes human HYPP. We now describe the Phe to Leu mutation in transmembrane domain IVS3 which courses the horse disease. This represents the first application of molecular genetics to an important horse disease, and the data will provide an opportunity for control or eradication of this condition.