In the stressed animal, the vasoactive hormones vasopressin and angiotensin-II and the neurotransmitter noradrenaline induce liver cells to release glucose from glycogen. The intracellular signal that links the cell-surface receptors for noradrenaline (alpha 1) and vasoactive peptides to activation of glycogenolysis is known to be a rise in the cytoplasmic concentration of free calcium ions (free Ca). The receptors for these agonists induce the hydrolysis of phosphatidylinositol 4,5-bisphosphate, a minor plasmalemma lipid, to produce inositol trisphosphate and diacylglycerol. Inositol trisphosphate has been shown to mobilize intracellular calcium in hepatocytes. We show here, by means of aequorin measurements in single, isolated rat hepatocytes, that the free Ca response to these agonists consists of a series of transients. Each transient rose within 3 s to a peak free Ca of at least 600 nM and had a duration of approximately 7 s. The transients were repeated at intervals of 0.3-4 min, depending on agonist concentration. Between transients, free Ca returned to the resting level of approximately 200 nM. Clearly, the mechanisms controlling free Ca in hepatocytes are more complex than hitherto suspected.

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The parthenogenetic activation of mouse oocytes by several agents is accompanied by a large rise in the intracellular calcium concentration ( [Ca2+]i). The tumour-promoting phorbol ester 12-O-tetradecanoyl phorbol acetate (TPA) activates some cellular processes which are also activated by raised [Ca2+] (ref. 2). We therefore tested TPA on mouse oocytes and found it to be a potent parthenogenetic activating agent. Recent reports suggest that TPA mimics endogenous diacylglycerol3 and can stimulate cells by activating protein kinase C without raising [Ca2+]i (refs 4, 5). We have now measured [Ca2+]i with aequorin in mouse oocytes treated with TPA. Sustained oscillations in [Ca2+]i appeared in those oocytes which were subsequently activated. We also measured [Ca2+]i during fertilization. The response began with [Ca2+]i transients as reported previously, but the transients continued in a regular pattern for 4 h. There was no rise in [Ca2+]i of the type induced by activating agents such as ethanol. One component of the fertilization response appears to be related to the TPA-induced oscillations.

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While we are still learning more about COVID-19, caused by the novel SARS-CoV-2 virus, finding alternative and already available methods to reduce the risk and severity of the disease is paramount. One such option is vitamin D, in the form of vitamin D 3 (cholecalciferol) supplementation, due to its potential antiviral properties. It has become apparent that older individuals have a greater risk of developing severe COVID-19, and compared to younger adults, the elderly have lower levels of vitamin D due to a variety of biological and behavioral factors. Older adults are also more likely to be diagnosed with Parkinson's disease (PD), with advanced age being the single greatest risk factor. In addition to its immune-system-modulating effects, it has been suggested that vitamin D supplementation plays a role in slowing PD progression and improving PD-related quality of life. We completed a review of the literature to determine the relationship between vitamin D, PD, and COVID-19. We concluded that the daily supplementation of 2000-5000 IU/day of vitamin D 3 in older adults with PD has the potential to slow the progression of PD while also potentially offering additional protection against COVID-19.

The fabrication of microelectrodes integrated within ultra-low-volume microtiter chambers for the amperometric determination of metabolites continues to be of interest in the subject of single-cell and high-throughput screening. The microsystem described in this paper consists of a two-microelectrode sensor with a microfluidic dispensation technology, which is able to deliver both very low titers (6.5 pL) and single heart cells into a low-volume microphotoelectrochemical cell. Devices were fabricated using photolithography and liftoff giving reproducible sensors integrated within high aspect ratio titer chambers (with a volume of 360 pL), made of the photoepoxy SU8. In this paper, the determination of lactate was optimized using an enzyme-linked assay based upon lactate oxidase, involving the amperometric determination of hydrogen peroxide at +640 mV versus an internal Ag/AgCl pseudoreference. The microsystem (including the microfluidic dispensers and structures as well as the microsensor) was subsequently used to measure the lactate content of single heart cells. Dynamic electrochemical measurements of lactate during cell permeabilization are presented. We also show the use of respiratory uncouplers to simulate ischemia in the single myocyte and show that, as expected, the rate of lactate production from the hypoxic heart cell is greater than that within the normoxic healthy myocyte.