Calcium ion activity and pH in the odontoblast-predentin region: ion-selective microelectrode measurements

Ca2+ ion activities and pH were measured in the odontoblast/predentin region of rat incisors by means of the microelectrode technique. In Ringer solution, the apparent resting membrane potential of odontoblasts was determined to be -24 +/- 4 mV (mean +/- SE), whereas the odontoblast intracellular pH was found to be 6.66 +/- 0.02. The values obtained are within the range of other cell types, as measured in similar incubating solutions. The pH in the extracellular predentin was higher than the intracellular pH, 7.00 +/- 0.02. The Ca2+ ion activity in predentin (pCa = 2.94 +/- 0.15) was found to be significantly (P less than 0.001) higher than that in the dental pulp extracellular fluid (pCa = 3.37 +/- 0.14). The 2-3 times higher calcium activity extracellularly in predentin, compared with the dental pulp, implies the existence of some ion-concentrating mechanism across the odontoblast layer in the direction of the mineralization front.