Faculty Bibliography

Recent evidence suggests that extracellular Ca2+ may modulate cell function in mineralized tissue. To determine whether dentinogenic cells, in particular, are sensitive to extracellular Ca2+, fura-2 microfluorometry was used to monitor intracellular calcium levels in odontoblasts freshly isolated from rat incisor. In response to applications of 0.5-4.0 mM extracellular calcium (CaCl2), most odontoblasts (84%; 107/128) showed an increase in intracellular calcium. For the majority of these cells (70%; 75/107), the typical response was biphasic; there was an initial, transient increase in intracellular calcium which reached peak levels within 30-50 s and decayed rapidly, followed by a slower (> 300 s) recovery toward basal levels. In general, the response of these cells to calcium was repeatable and the mean calcium concentration for the half-maximal response was approximately 1.3 mM. This effect could be partially blocked by either 200 microM lanthanum, a nonspecific blocker of Ca2+ channels, or 20 microM dantrolene, a potent inhibitor of Ca2+ release from internal stores. Used in combination, lanthanum, and dantrolene nearly abolished the calcium response completely. In addition, this response was sensitive to the dihydropyridine-sensitive calcium channel blocking agent nicardipine (60 microM), indicating a role for voltage-gated calcium channels during these events. These results show that odontoblasts respond to external calcium through mechanisms involving both influx of external calcium as well as release of calcium from internal stores and suggest a role for extracellular calcium in regulating the function of these cells

A perforated root represents a difficult challenge to the clinician, and treatment of such defects often involves surgical and/or advanced restorative techniques. This typically requires a series of lengthy, often stressful appointments, may compromise esthetics, and invariably involves additional costs to the patient. This case report describes the nonsurgical treatment of separate mechanical perforations that resulted from the removal of a failed prefabricated post. The tooth was restored in a minimum number of visits through the use of a novel application of a resin-ionomer material originally designed for routine restorative procedures

It has been suggested that understanding the physiological properties of odontoblasts may be important in understanding the mechanisms underlying both metabolic and transductive processes in dental pulp. Because ion flux(es) may play a critical role in these events, it is of particular interest to understand ionic mechanisms in odontoblast cells. Thus, the aim of this study was to use patch-clamp recording techniques to examine the properties of resident ion channels in freshly dissociated odontoblasts. In recordings made in potassium-rich solutions, cells displayed at least three distinct channel amplitudes, with conductances of 130 +/- 18 pS, 52 +/- 4 pS, and 25 +/- 2 pS, respectively. Channel activity persisted in the presence of potassium salts of impermeant anions, and could be abolished by barium, a non-specific potassium channel blocker. In addition to the potassium conductances, we saw two separate anion channels in the odontoblast membrane. These channels were predominantly chloride-selective, weakly permeable to both acetate and aspartate, and had conductances of 391 +/- 64 pS and 24 +/- 3 pS. While questions remain regarding the functional role of these and other ion channels that presumably reside in the odontoblast membrane, our results demonstrate that it is possible to study ionic mechanisms of the odontoblast at the level of the single cell.

An experimental method has been established to measure the electric properties of a cell membrane by combination of patch clamp and dual-wavelength ratio imaging of a fluorescent potentiometric dye, 1-(3-sulfonatopropyl)-4-[beta[2-(di-n-octylamino)-6-naphthyl]vinyl ]pyridinium betaine (di-8-ANEPPS). Pairs of fluorescence images from the dye-stained membrane of neuroblastoma N1E-115 cells excited at two wavelengths were initially obtained to calculate ratio images corresponding to the resting transmembrane potential. Subsequently, a whole-cell patch was established and the membrane potential clamped to levels varying from -100 to +60 mV; at each voltage, a pair of dual-wavelength images were acquired to develop a calibration of the fluorescence ratio. Using this method, the resting potentials could accurately be measured showing that the differentiated cells were 17 mV more polarized than undifferentiated cells. The combination of electrical and optical methods can also follow changes in other membrane electric properties, such as dipole potential, and thus permit a detailed analysis of the membrane electrical properties underlying the voltage regulation of ion channels.