Cultured smooth muscle cells obtained from rat lung periphery (RPC) and proximal pulmonary artery (RSMC) expressed mRNA for serotonin (5-HT) type 2 receptor (5-HT2) and 5-HT transporter (by Northern blot analysis). Functional expression of these genes was evident since both cell types 1) bound 125I-labeled lysergic acid diethylamide (LSD; 5-HT2 receptor antagonist) that was equally effectively displaced by either ketanserin or mianserin; and 2) transported 5-[3H]HT in an imipramine-sensitive manner. Serotonin (10(-9)-10(-5) M) stimulated DNA synthesis (as measured by [3H]thymidine uptake) in RPC and RSMC. The 5-HT-induced increase in DNA synthesis was significantly inhibited in both cell types by the 5-HT2 receptor antagonist, ketanserin (10(-7)-10(-6) M), and by fluoxetine (10(-6) M), a putative 5-HT transport inhibitor. Acute exposure to 5-HT (1-100 microM) caused an abrupt rise in intracellular calcium ([Ca2+]i) in single pulmonary vascular smooth muscle cells as microspectrofluorometrically determined using the calcium-sensitive dye, fura 2. The 5-HT-induced change in [Ca2+]i was completely abolished in the presence of 10(-6) M ketanserin as well as imipramine or fluoxetine (10(-6) M). The calcium transients due to 5-HT persisted in a Na(+)-free condition (in which the transporter activity was completely abolished) and imipramine and fluoxetine (and ketanserin) were effective inhibitors of 5-HT under these conditions. Therefore, the 5-HT2 receptor, but not the transporter, is responsible for initiating the acute effects (e.g., calcium transients) of 5-HT in cultured rat pulmonary vascular smooth muscle cells and fluoxetine (1 microM) may have 5-HT2-receptor antagonist properties.(ABSTRACT TRUNCATED AT 250 WORDS)