Hormonally-regulated expression of voltage-operated Ca2+ channels in osteocytic (MLO-Y4) cells

Voltage operated calcium channels (VOCCs) are important in stimulus-response coupling in osteoblasts. We have investigated the expression of VOCCs in the mouse osteocyte cell line, MLO-Y4. Using the whole-cell patch clamp technique we were unable to detect any VOCC currents (n = 436) even in the presence of the L-type VOCC agonist Bay K 8644 (n = 350). Reverse transcription polymerase chain reaction (RT-PCR), using primers to detect alpha (1C), alpha (1D), and alpha (1G) VOCC subunits tall of which are expressed in primary osteoblasts), did not generate detectable products with mRNA from MLO-Y4 cells. However, after treatment with physiological levels of hormones, VOCC alpha (1) subunit mRNAs were detected in MLO-Y4 cells. PTH, 17 beta -estradiol, and dexamethasone-treatment induced expression of L-type (alpha (1C), alpha (1D)) subunit transcripts. ATP-treatment induced expression of T-type ((YIG) transcripts. Using whole-cell patch clamp we detected VOCC currents in 5-10% of cells after treatment. Current characteristics (L- or T-type) were consistent with the transcript expressed. (C) 2001 Academic Press.