Role of Trpc channels, Stim1 and Orai1 in PGF(2α)-induced calcium signaling in NRK fibroblasts.

Normal rat kidney (NRK) fibroblasts exhibit growth-dependent changes in electrophysiological properties and intracellular calcium dynamics. The transition from a quiescent state to a density-arrested state results in altered calcium entry characteristics. This coincides with modulation of the expression of the genes encoding the calcium channels Trpc1, Trpc6 and Orai1, and of the intracellular calcium sensor Stim1.

Different roles of inositol 1,4,5-trisphosphate receptor subtypes in prostaglandin F(2alpha)-induced calcium oscillations and pacemaking activity of NRK fibroblasts.

We investigated the role of inositol 1,4,5-trisphosphate (IP(3))-receptor isoforms in the prostaglandin F(2alpha) (PGF(2alpha))-induced calcium oscillations and pacemaking activity of normal rat kidney (NRK) fibroblasts. Reverse transcription polymerase chain reaction (RT-PCR) studies revealed that NRK fibroblasts express only the IP(3)-receptor subtypes IP(3)R1 and IP(3)R3. Quantitative RT-PCR analysis demonstrated that their expression levels varied as a function of the growth status of NRK cells; NRK cells made quiescent (Q) by serum deprivation expressed significantly higher levels of subtypes 1 and 3 than cells grown to density-arrest (DA).

Growth-dependent modulation of capacitative calcium entry in normal rat kidney fibroblasts.

Normal rat kidney (NRK) fibroblasts have electrophysiological properties and intracellular calcium dynamics that are dependent upon their growth stage. In the present study we show that this differential behavior coincides with a differential calcium entry that can be either capacitative or non-capacitative. Confluent cells made quiescent by serum deprivation, which have a stable membrane potential near -70 mV and do not show spontaneous intracellular calcium oscillations, primarily exhibit the capacitative mechanism for calcium entry, also called store-operated calcium entry (SOCE).

Role of the prostanoid FP receptor in action potential generation and phenotypic transformation of NRK fibroblasts.

By using an shRNA approach to knockdown the expression of the prostaglandin (PG)-F(2alpha) receptor (FP-R), the role of PGF(2alpha) in the process of phenotypic transformation of normal rat kidney (NRK) fibroblasts has been studied. Our data show that PGF(2alpha) up-regulates Cox-2 expression both at the mRNA and protein level, indicating that activation of FP-R in NRK fibroblasts induces a positive feedback loop in the production PGF(2alpha). Knockdown of FP-R expression fully impaired the ability of PGF(2alpha) to induce a calcium response and subsequent depolarization in NRK cells.

Local induction of pacemaking activity in a monolayer of electrically coupled quiescent NRK fibroblasts.

Cultures of normal rat kidney (NRK) fibroblasts may display spontaneous calcium action potentials which propagate throughout the cellular monolayer. Pacemaking activity of NRK cells was studied by patch clamp electrophysiology and vital calcium imaging, using a new experimental approach in which a ring was placed on the monolayer in order to physically separate pacemakers within or under the ring and follower cells outside the ring. Stimulation of cells inside the ring with IP(3)-generating hormones such as prostaglandin F(2alpha) (PGF(2alpha)) resulted in the induction of periodic action potentials outside the ring, which were abolished when the L-type calcium channel blocker nifedipine was added outside the ring, but not inside the ring.