INTRACELLULAR CALCIUM IN CULTURED RABBIT OVIDUCT EPITHELIAL-CELLS

Oviduct fluid is the medium in which fertilization and early embryonic development occur but little is known about the ionic basis of fluid secretion or its control. Since calcium ions (Ca2+) are involved in th e mechanism of secretion in other epithelia, the intracellular calcium concentration ([Ca2+](i)) was measured in single, rabbit oviduct epit helial cells in primary culture using the fluorescent dye Fura-2. The resting [Ca2+](i) was constant (115 nM) in cells cultured for 2-7 days . Ion substitution experiments demonstrated the presence of a Na+/Ca2-exchange system in the plasma membrane, whereas influx through channe ls was found to have only a minor role in maintaining the resting [Ca2 +](i). The addition of dibutyryl cAMP (db cAMP) induced two types of r esponse: the first was an increase in [Ca2+](i), dependent on the pres ence of extracellular Ca2+, and the second was a zero response. Extrac ellular ATP induced a transient increase in [Ca2+](i) owing to the rel ease of Ca2+ from intracellular stores and Ca2+ entering the cell acro ss the plasma membrane. It is proposed that these effects may be due t o the presence of two types of cell in culture-the ciliated and non-ci liated (secretory type) oviduct epithelial cells.