DYNAMIC CHANGES IN SPONTANEOUS INTRACELLULAR FREE CALCIUM OSCILLATIONS AND THEIR RELATIONSHIP TO PROLACTIN GENE-EXPRESSION IN SINGLE, PRIMARY MAMMOTROPES

Cytosolic calcium plays a critical role in the control of a number of genes, including that of the pituitary hormone PRL. Cells that secrete this hormone, termed mammotropes, display spontaneous oscillations of intracellular free calcium ([Ca2+](i)) that are positively correlated to PRL release. However, the precise contribution of calcium signalin g to the expression of any gene including PRL has remained obscure owi ng to the requirement for and lack of a strategy for monitoring both o f these dynamic variables (gene expression and [Ca2+](i) oscillations) in the same living cell. In the present study, we overcame this techn ical limitation by making real-time measurements of PRL gene expressio n in transfected, primary rat mammotropes previously subjected to [Ca2 +](i) determinations by digital imaging fluorescence microscopy of fur a-2. Our results showed that the majority of mammotropes (75%) exhibit ed distinct oscillatory behaviors that could be subgrouped on the basi s of frequency/amplitude of [Ca2+](i) changes, whereas the remainder ( 25%) were quiescent (nonoscillatory). Interestingly, most mammotropes displayed spontaneous transitions between oscillatory and quiescent st ates over the course of several hours. As a consequence of this oscill atory plasticity, there was not a positive correlation between [Ca2+]( i) dynamics and gene expression at any point in time, as would be pred icted by studies with entire populations of cells. Instead, the relati onship was distinctly inverse, suggesting that dynamic changes in PRL gene expression may be regulated by temporally dissociated transitions between quiescent and oscillatory states.