Changes of intracellular calcium concentrations by phenylephrine in renal arterial smooth muscle cells

In smooth muscle cells isolated from swine renal interlobar arteries, pheny lephrine (PE) at concentrations of 1-10 mu M produced biphasic increases of the intracellular calcium concentration. An early transient rise was follo wed by a maintained plateau. The maintained component was sensitive to extr acellular calcium, in contrast to the early transient, which was still obse rved in nominally calcium-free solution. Nifedipine (1 mu M) and NiCl2 (100 mu M) only weakly affected the calcium signal, suggesting that voltage-sen sitive calcium channels play only a minor role in the PE-induced changes in intracellular calcium. Thapsigargin (0.5 mu M) elevated the intracellular calcium concentration and depressed both the early transient and the mainta ined component of the PE response. In calcium-free medium PE induced a tran sient rise of the intracellular calcium concentration with a depressed plat eau. Readmission of calcium elevated the intracellular calcium concentratio n above the baseline. Both components of the PE-induced calcium signal were completely abolished when the cells were pretreated with the phospholipase C (PLC) inhibitor U73122 (2 mu M). LaCl3 (100 mu M, 1 mM), an inhibitor of calcium-release-activated current (I-CRAC), had no effect on the PE-induce d calcium signal. GdCl3 (50 mu M), SKF 96365 (10 mu M) and flufenamic acid (100 mu M), reported to inhibit nonselective cation channels, blocked or tr ansiently reduced the maintained calcium signal. Several protein kinase inh ibitors such as genistein (10 mu M), H7 (50 mu M), 1-189 (1 mu M) and bisin dolylmaleimide (0.2 mu M) reduced the maintained calcium signal. We conclud e that the initial transient spike of the PE-induced calcium signal is due to release of calcium from inositol 1,4,5-trisphosphate-sensitive calcium s tores evoked by alpha(1)-adrenoceptor-coupled stimulation of PLC and that t he maintained component is due to capacitative calcium entry, which is modu lated by protein kinases.