α 1 ‐Adrenoceptor effects mediated by protein kinase C α in human cultured prostatic stromal cells

We have investigated the effects of α 1 ‐adrenoceptor stimulation upon contractility, Ca 2+ influx, inositol phosphate production, and protein kinase C (PKC) translocation in human cultured prostatic stromal cells (HCPSC). The α 1 ‐adrenoceptor selective agonist phenylephrine elicited contractile responses of HCPSC, i.e. a maximal cell shortening of 45±6% of initial cell length, with an EC 50 of 1.6±0.1 μ M . The α 1 ‐adrenoceptor selective antagonists prazosin (1 μ M ) and terazosin (1 μ M ) both blocked contractions to phenylephrine (10 μ M ). The L‐type calcium channel blocker nifedipine (10 μ M ), and the PKC inhibitors Gö 6976 (1 μ M ) and bisindolylmaleimide (1 μ M ) also inhibited phenylephrine‐induced contractions. Phenylephrine caused a concentration dependent increase in inositol phosphate production (EC 50 119±67 n M ). This response was blocked by terazosin (1 μ M ). Phenylephrine caused the translocation of the PKC α isoform, but not the β, δ, γ, ε or λ isoforms, from the cytosolic to the particulate fraction of HCPSC, with an EC 50 of 5.7±0.5 μ M . In FURA‐2AM (5 μ M ) loaded cells, phenylephrine elicited concentration dependent increases in [Ca 2+ ] i , with an EC 50 of 3.9±0.4 μ M . The response to phenylephrine (10 μ M ) was blocked by prazosin (1 μ M ), bisindolymaleimide (1 μ M ), and nifedipine (10 μ M ). In conclusion, this study has shown that HCPSC express functional α 1 ‐adrenoceptors, and that the intracellular pathways responsible for contractility may be largely dependent upon protein kinase C activation and subsequent opening of L‐type calcium channels.British Journal of Pharmacology (2003) 138 , 218–224. doi: 10.1038/sj.bjp.0705021