Roles of mitochondria and temperature in the control of intracellular calcium in adult rat sensory neurons.

We recorded Ca2+ current and intracellular Ca2+ ([Ca2+](i)) in isolated adult rat dorsal root ganglion (DRG) neurons at 20 and 30 degrees C. In neurons bathed in tetraethylammonium and dialyzed with cesium, warming reduced resting [Ca2+](i) from 87 to 49 nM and the time constant of the decay of [Ca2+](i) transients (tau(r)) from 1.3 to 0.99s (Q(10)=1.4). The Buffer Index, the ratio between Ca2+ influx and Delta[Ca2+](i) (f I(ca)d(t)/Delta[Ca2+]i) , increased two- to threefold with warming. Neither inhibition of the plasma membrane Ca2+ -ATPase by intracellular sodium orthovanadate nor inhibition of Ca2+ uptake by the endoplasmic reticulum by thapsigargin plus ryanodine were necessary for the effects of warming on these parameters. In contrast, inhibition of the mitochondrial Ca2+ uniporter by intracellular ruthenium red largely reversed the effects of warming. Carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP, 500 nM) increased resting [Ca2+](i) at 30 degrees C. Ten millimolar intracellular sodium prolonged the recovery of [Ca2+](i) transients to 10-40s. This effect was reversed by an inhibitor of mitochondrial Na(+)/Ca2+ -exchange (CGP 37157, 10 microM). Thus, mitochondrial Ca2+ uptake is necessary for the temperature-dependent increase in Ca2+ buffering and mitochondrial Ca2+ fluxes contribute to the control of [Ca2+](i) between 50 and 150 nM at 30 degrees C.

An Excel-based model of Ca2+ diffusion and fura 2 measurements in a spherical cell.

We wrote a program that runs as a Microsoft Excel spreadsheet to calculate the diffusion of Ca2+ in a spherical cell in the presence of a fixed Ca2+ buffer and two diffusible Ca2+ buffers, one of which is considered to be a fluorescent Ca2+ indicator. We modeled Ca2+ diffusion during and after Ca2+ influx across the plasma membrane with parameters chosen to approximate amphibian sympathetic neurons, mammalian adrenal chromaffin cells, and rat dorsal root ganglion neurons. In each of these cell types, the model predicts that spatially averaged intracellular Ca2+ activity ([Ca2+]avg) rises to a high peak and starts to decline promptly on the termination of Ca2+ influx. We compared [Ca2+]avg with predictions of ratiometric Ca2+ measurements analyzed in two ways. Method 1 sums the fluorescence at each of the two excitation or emission wavelengths over the N compartments of the model, calculates the ratio of the summed signals, and converts this ratio to Ca2+ ([Ca2+]avg,M1). Method 2 sums the measured number of moles of Ca2+ in each of the N compartments and divides by the volume of the cell ([Ca2+]avg,M2). [Ca2+]avg,M1 peaks well after the termination of Ca2+ influx at a value substantially less than [Ca2+]avg because the summed signals do not reflect the averaged free Ca2+ if the signals come from compartments containing gradients in free Ca2+ spanning nonlinear regions of the relationship between free Ca2+ and the fluorescence signals. In contrast, [Ca2+]avg,M2 follows [Ca2+]avg closely.

A historical perspective on the discovery of adenyl purines.

In 1929, Drury and Szent-Gyorgyi described the effects of a simple extract of heart muscle and other tissues on the mammalian heart. This extract was identified as adenylic acid and found to have profound effects on the cardiovascular system. The discovery and identification of adenyl purines and their effects on the cardiovascular system has now extended to other biological functions such as neurotransmission, neuromodulation, and endocrine/exocrine secretory functions and beyond. This review examines the history of the discovery and identification of the many roles played by adenyl purines in regulation of physiological homeostasis.

Pain: neuroanatomy, chemical mediators, and clinical implications.

Most pain information begins at simple, naked nerve endings called nociceptors that form a functional pain unit with nearby tissue capillaries and mast cells. Tissue injury causes these nerve terminals to depolarize, an event that is propagated along the entire afferent fiber eventuating in sensory impulses reaching the spinal cord. This firing of primary afferent fibers at the site of tissue injury causes axonal release of vesicles containing neuropeptides such as substance P, which acts in an autocrine and paracrine manner to sensitize the nociceptor and increase its rate of firing. Cellular damage and inflammation increase concentrations of other chemical mediators such as histamine, bradykinin, and prostaglandins in the area surrounding functional pain units. These additional mediators act synergistically to augment the transmission of nociceptive impulses along sensory afferent fibers. Primary fibers travel from the periphery to the dorsal horn where they synapse on secondary neurons and interneurons. When activated, interneurons exert inhibitory influences on further pain signal trafficking. Efferent supraspinal influences, in turn, determine the activity of interneurons by releasing a variety of neurotransmitter substances, thus resulting in a high degree of modulation of nociception within the dorsal horn. Events occurring in the periphery and in the dorsal horn can cause a dissociation of pain perception from the presence or degree of actual tissue injury. These phenomena involve many chemical mediators and receptor systems, and can increase pain experience qualitatively, quantitatively, temporally, and spatially. The complexity and plasticity of the nociceptive system can make clinical management of pain difficult. Undestanding the structure and chemical signals associated with this system can improve the use of existing analgesics and provide targets for development of newer and more specific pain-fighting drugs.