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Differential Expression of Ionic Channels in Rat Anterior Pituitary Cells

Endocrinology and Reproduction Research Branch National Institute of Child Health and Human Development National Institutes of Health Bethesda, Maryland 20892-4510

Secretory anterior pituitary cells are of the same origin, but exhibit cell type-specific patterns of spontaneous intracellular Ca²⁺ signaling and basal hormone secretion. To understand the underlying ionic mechanisms mediating these differences, we compared the ionic channels expressed in somatotrophs, lactotrophs, and gonadotrophs from randomly cycling female rats under identical cell culture and recording conditions. Our results indicate that a similar group of ionic channels are expressed in each cell type, including transient and sustained voltage-gated Ca²⁺ channels, tetrodotoxin-sensitive Na⁺ channels, transient and delayed rectifying K⁺ channels, and multiple Ca²⁺-sensitive K⁺ channel subtypes. However, there were marked differences in the expression levels of some of the ionic channels. Specifically, lactotrophs and somatotrophs exhibited low expression levels of tetrodotoxin-sensitive Na⁺ channels and high expression levels of the large-conductance, Ca²⁺-activated K⁺ channel compared with those observed in gonadotrophs. In addition, functional expression of the transient K⁺ channel was much higher in lactotrophs and gonadotrophs than in somatotrophs. Finally, the expression of the transient voltage-gated Ca²⁺ channels was higher in somatotrophs than in lactotrophs and gonadotrophs. These results indicate that there are cell type-specific patterns of ionic channel expression, which may be of physiological significance for the control of Ca²⁺ homeostasis and secretion in unstimulated and receptor-stimulated anterior pituitary cells.

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