Transcription of herpes simplex virus (HSV) immediate-early (IE) genes does not occur in sensory neurons latently infected with the virus or following infection of neuronal cell lines. In neuronal cell lines this inability results from the weak activity of the viral IE promoters, which is caused by a neuron-specific repressor factor that binds specifically to the TAATGARAT motif in these promoters and to related octamer elements. Cells expressing this repressor contain an additional octamer-binding protein that is absent from permissive cells. We identify this factor as the lymphocyte- and neuron-specific octamer-binding protein Oct-2 and show that Oct-2 mRNA is also present in dorsal root ganglion neurons, the natural site of HSV latency in vivo. Moreover, artificially elevated expression of Oct-2 can repress the IE promoter. The potential role of Oct-2 in the initiation and maintenance of in vivo latent infection with HSV is discussed.

Key points The role of trimeric intracellular cation (TRIC) channels is not known, although evidence suggests they may regulate ryanodine receptors (RyR) via multiple mechanisms. We therefore investigated whether Tric‐a gene knockout (KO) alters the single‐channel function of skeletal RyR (RyR1).We find that RyR1 from Tric‐a KO mice are more sensitive to inhibition by divalent cations, although they respond normally to cytosolic Ca2+, ATP, caffeine and luminal Ca2+.In the presence of Mg2+, ATP cannot effectively activate RyR1 from Tric‐a KO mice.Additionally, RyR1 from Tric‐a KO mice are not activated by protein kinase A phosphorylation, demonstrating a defect in the ability of β‐adrenergic stimulation to regulate sarcoplasmic reticulum (SR) Ca2+‐release.The defective RyR1 gating that we describe probably contributes significantly to the impaired SR Ca2+‐release observed in skeletal muscle from Tric‐a KO mice, further highlighting the importance of TRIC‐A for normal physiological regulation of SR Ca2+‐release in skeletal muscle. AbstractThe type A trimeric intracellular cation channel (TRIC‐A) is a major component of the nuclear and sarcoplasmic reticulum (SR) membranes of cardiac and skeletal muscle, and is localized closely with ryanodine receptor (RyR) channels in the SR terminal cisternae. The skeletal muscle of Tric‐a knockout (KO) mice is characterized by Ca2+ overloaded and swollen SR and by changes in the properties of SR Ca2+ release. We therefore investigated whether RyR1 gating behaviour is modified in the SR from Tric‐a KO mice by incorporating native RyR1 into planar phospholipid bilayers under voltage‐clamp conditions. We find that RyR1 channels from Tric‐a KO mice respond normally to cytosolic Ca2+, ATP, adenine, caffeine and to luminal Ca2+. However, the channels are more sensitive to the inactivating effects of divalent cations, thus, in the presence of Mg2+, ATP is inadequate as an activator. Additionally, channels are not characteristically activated by protein kinase A even though the phosphorylation levels of Ser2844 are similar to controls. The results of the present study suggest that TRIC‐A functions as an excitatory modulator of RyR1 channels within the SR terminal cisternae. Importantly, this regulatory action of TRIC‐A appears to be independent of (although additive to) any indirect consequences to RyR1 activity that arise as a result of K+ fluxes across the SR via TRIC‐A.

The ryanodine receptor (RyR) is the pathway for release of the sarcoplasmic reticulum (SR) Ca 2þ required for cardiac and skeletal muscle contraction. The opening of SR K þ channels is thought to support this process. Movements of the RyR and SR K þ channel gates required for channel opening and closing will be dependent on the biophysical properties of the SR membrane which, in turn, will be affected by factors such as temperature and membrane composition. Cardiac RyR channel opening is hypersensitive to temperature changes (Sitsapesan et al., 1991, J Physiol., 434:469-488) although single-channel recordings are invariably performed at room temperature. We have therefore incorporated mammalian cardiac and skeletal RyR and SR K þ channels into bilayers under voltage-clamp conditions to investigate the effects of changing temperature and membrane lipid composition on single-channel behaviour. Changing bilayer lipid composition from phosphatidylethanolamine (PE) only, to a more physiological composition containing a 5:4:1 ratio of PE: phosphatidylserine (PS): phosphatidylcholine (PC) at 23 o C, significantly increased the open probability (Po) and single channel conductance of both channels. For example, RyR Po increased from 0.0650.03 to 0.2650.08 (n=8; SEM; P<0.05). With bilayer lipid ratio of 5 PE: 4 PS: 1 PC, raising temperature from 10 o C to 37 o C caused a graded decrease in RyR Po. In contrast, SR K þ channels exhibited non-linear changes in Po with a minimum at approximately 23 o C. Our results demonstrate the importance of investigating intracellular ion channel function at physiological temperatures and show that changes in SR membrane lipid composition markedly influence the behaviour of ion channels in the SR.

A symptomatic bone stress reaction is an early pathological feature, which can lead to stress fractures. It typically affects bones of the lower limbs in response to unaccustomed disproportional compressive loading. Professional sportspeople are susceptible to both bone stress reaction and stress fractures, where training regimes and competition predispose to overuse injuries. We discuss a unique case of a professional cricketer developing pain in the throwing arm due to bone stress reaction in the distal humerus, as confirmed on MRI. Modification of the patient’s training regime, presented in this case, facilitated complete recovery within 6 weeks. The positive response to modified training suggests a biomechanical origin of the pain. This case illustrates that tensile stress associated with throwing activities can result in a symptomatic bone stress reaction of the humerus in elite cricketers.

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