B1 AND B2 KININ RECEPTORS MEDIATE DISTINCT PATTERNS OF INTRACELLULAR CA2-MUSCLE CELLS( SIGNALING IN SINGLE CULTURED VASCULAR SMOOTH)

Stimulation of St and B2 kinin receptors on cultured rabbit superior m esenteric artery smooth muscle cells with des-Arg9-bradykinin (DBK) an d bradykinin (BK), respectively, results in significantly different pa tterns of intracellular Ca2+ mobilization. Single-cell fluorescence im aging of Fura-P-loaded cells revealed that although both DBK and BK in itially triggered similar rapid increases in cytosolic free Ca2+, the DBK response was biphasic and sustained, whereas the BK response was t ransient. The DBK response was maintained for greater than or equal to 20 min with the second phase characterized by an elevated plateau and /or base-line oscillations. The BK response was limited to an initial transient peak with the exception of a few cells, which after a prolon ged latency period, exhibited weak but regular base-line oscillations. The initial BK- and DBK-stimulated rises in cytosolic free Ca2+ were dependent on the release of Ca2+ from intracellular stores that seemed to be common for the two agonists. On the other hand, the continuatio n of the sustained phase of the DBK response required the influx of ex tracellular Ca2+, as well as continuous receptor occupancy by the agon ist. Stimulation of cells with DBK followed by washing and restimulati on with the same agonist within less than or equal to 2 min resulted i n a second B1 receptor response that was not significantly different f rom the first response. In contrast, the same protocol with BK yielded a dramatically decreased second B2 receptor response. This attenuatio n did not seem to be due to a lack of Ca2+ in the agonist-sensitive in tracellular stores because DBK elicited a full response after BK stimu lation. This study shows that in single cultured RSMA smooth muscle ce lls, agonist stimulation of B1 receptors generates a sustained intrace llular Ca2+ signal, whereas stimulation of B2 receptors promotes rapid and homologous desensitization, resulting in a transient Ca2+ signal. These distinct receptor-specific patterns of Ca2+ mobilization imply significantly different roles for B1 and B2 kinin receptors in vascula r smooth muscle cells.