This investigation aimed to examine the source of Ca(2+) mobilization that leads to the contractile response to either exogenously added histamine (1I?M-1mM) or electrical field stimulation (10Hz, 0.5ms, 60V). Removal of extracellular Ca(2+) by removal of Ca(2+) from the bathing medium reduced histamine (1mM) induced responses by 34 and responses induced by electrical field stimulation by 94 . Similarly, blockade of L-type Ca(2+) channels by nifedipine (1I?M) reduced histamine (1mM) induced responses by 43 and responses induced by electrical field stimulation by 77 . Application of cyclopiazonic acid (CPA) (10I?M) to inhibit Ca(2+) reuptake to the sarcoplasmic reticulum enhanced both histamine-induced and electrical field stimulation induced responses to a small degree, while the addition of the inosotol triphosphate (IP(3)) receptor antagonist, 2-aminophenoxyethane borane (2-APB) (100I?M) inhibited histamine induced responses by 70 and electrical field stimulation induced responses by 57 . Ryanodine (1I?M) did not affect contractile responses to either histamine or electrical field stimulation, either in the absence or presence of 2-APB (100I?M). During both histamine and electrical field stimulation induced contractions, prostate smooth muscle generates IP(3) receptor mediated Ca(2+) release in conjunction with Ca(2+) entry from the extracellular environment. Ryanodine receptors on the other hand, appear not to play a role in this physiological mechanism.